RabGTPase is a member of the Ras superfamily of small GTPases, which share a GTP-binding pocket containing highly conserved motifs that promote GTP hydrolysis. In Arabidopsis, the RabA group, which corresponds to the Rab11 group in animals, functions in the recycling of endosomes that control docking and fusion during vesicle transport. However, their molecular mechanisms remain unknown. In this study, we determined the crystal structures of the GDP-bound inactive form and both GppNHp- and GTP-bound active forms of RabA1a, at resolutions of 2.8, 2.6, and 2.6 A, respectively. A bound sulfate ion in the active site of the GDP-bound structure stabilized Switch II by bridging the interaction between a magnesium ion and Arg74. Comparisons of the two states of RabA1a with Rab11 proteins revealed clear differences in the Switch I and II loops. These results suggested that conformational change of the Switch regions of RabA1a, derived by GTP or GDP binding, could maintain subcellular membrane traffic through the specific interaction of effector molecules.

The plant circadian clock regulates the rhythms of plant metabolism. Many herbivore‐induced plant volatiles (HIPVs) fluctuate, diurnally, but the role of the circadian clock in the emission of HIPVs and their ecological consequences remains largely unknown. Here, we show that the timing of herbivore attack can alter the outcome of tri‐trophic interactions, and this is mediated by the circadian clock, under both field and glasshouse conditions. Although most HIPV emissions did not have a circadian rhythm, the circadian clock modulated HIPV emissions in a time‐dependent manner. HIPVs mediate tri‐trophic interactions, and the circadian clock may affect these interactions by modulating HIPV emission in nature.

Modifications of inflorescence architecture have been crucial for the successful domestication of wheat and barley, which are central members of the Triticeae tribe that provide essential grains for the human diet. Investigation of the genes and alleles that underpin domestication-related traits has provided valuable insights into the molecular regulation of inflorescence development of the Triticeae, and further investigation of modified forms of architecture are proving to be equally fruitful. The identified genes are involved in diverse biological processes, including transcriptional regulation, hormone biosynthesis and metabolism, post-transcriptional and post-translational regulation, which alter inflorescence architecture by modifying the development and fertility of lateral organs, called spikelets and florets. Recent advances in sequencing capabilities and the generation of mutant populations are accelerating the identification of genes that influence inflorescence development, which is important given that genetic variation for this trait promises to be a valuable resource for optimizing grain production. This review assesses recent advances in our understanding of the genes controlling inflorescence development in wheat and barley, with the aim of highlighting the importance of improvements in developmental biology for optimizing the agronomic performance of staple crop plants.

Optimizing leaf shape is a major challenge in efforts to develop an ideal plant type. Cucumber leaf shapes are diverse; however, the molecular regulatory mechanisms underlying leaf shape formation are unknown. In this study, we obtained a round leaf mutant (rl) from an ethyl methanesulfonate‐induced mutagenesis population. Genetic analysis revealed that a single recessive gene, rl, is responsible for this mutation. A modified MutMap analysis combined linkage mapping identified a single nucleotide polymorphism within a candidate gene, Csa1M537400, as the mutation underlying the trait. Csa1M537400 encodes a PINOID kinase protein involved in auxin transport. Expression of Csa1M537400 was significantly lower in the rl mutant than in wild type, and it displayed higher levels of IAA (indole‐3‐acetic acid) in several tissues. Treatment of wild‐type plants with an auxin transport inhibitor induced the formation of round leaves, similar to those in the rl mutant. Altered expression patterns of several auxin‐related genes in the rl mutant suggest that rl plays a key role in auxin biosynthesis, transport, and response in cucumber. These findings provide insight into the molecular mechanism underlying the regulation of auxin signaling pathways in cucumber, and will be valuable in the development of an ideal plant type.

YUC flavin monooxygenases catalyze the rate‐limiting step of auxin biosynthesis. Here we report the vacuolar targeting and degradation of GFP‐YUC1. GFP‐YUC1 fusion expressed in Arabidopsis protoplasts or transgenic plants was primarily localized in vacuoles. Surprisingly, we established that GFP‐YUC1, a soluble protein, was sorted to vacuoles through the ESCRT pathway, which has long been recognized for sorting and targeting integral membrane proteins. We further show that GFP‐YUC1 was ubiquitinated and in this form GFP‐YUC1 was targeted for degradation, a process that was also stimulated by elevated auxin levels. Our findings revealed a molecular mechanism of GFP‐YUC1 degradation and demonstrate that the ESCRT pathway can recognize both soluble and integral membrane proteins as cargoes.

Grass species display a wide array of inflorescences ranging from highly branched compound/panicle inflorescences to unbranched spike inflorescences. The unbranched spike is a characteristic feature of the species of tribe Triticeae, including economically important crops, such as wheat and barley. In this review, we describe two important developmental genetic mechanisms regulating spike inflorescence architecture in barley and wheat. These include genetic regulation of (i) row-type pathway specific to Hordeum species and (ii) unbranched spike development in barley and wheat. For a comparative understanding, we describe the branched inflorescence phenotypes of rice and maize along with unbranched Triticeae inflorescences. In the end, we propose a simplified model describing a probable mechanism leading to unbranched spike formation in Triticeae species.

A plant's lateral structures, such as leaves, branches and flowers, literally hinge on the shoot axis, making its integrity and growth fundamental to plant form. In all plants, subapical proliferation within the shoot tip displaces cells downward to extrude the cylindrical stem. Following the transition to flowering, many plants show extensive axial elongation associated with increased subapical proliferation and expansion. However, the cereal grasses also elongate their stems, called culms, due to activity within detached intercalary meristems which displaces cells upward, elevating the grain-bearing inflorescence. Variation in culm length within species is especially relevant to cereal crops, as demonstrated by the high-yielding semi-dwarfed cereals of the Green Revolution. Although previously understudied, recent renewed interest the regulation of subapical and intercalary growth suggests that control of cell division planes, boundary formation and temporal dynamics of differentiation, are likely critical mechanisms coordinating axial growth and development in plants.

Plant peroxisomes are unique subcellular organelles which play an indispensable role in several key metabolic pathways, including fatty acid β-oxidation, photorespiration, and degradation of reactive oxygen species. The compartmentalization of metabolic pathways into peroxisomes is a strategy for organizing the metabolic network and improving pathway efficiency. An important prerequisite, however, is the exchange of metabolites between peroxisomes and other cell compartments. Since the first studies in the 1970s scientists contributed to understanding how solutes enter or leave this organelle. This review gives an overview about our current knowledge of the solute permeability of peroxisomal membranes described in plants, yeast, mammals and other eukaryotes. In general, peroxisomes contain in their bilayer membrane specific transporters for hydrophobic fatty acids (ABC transporter) and large cofactor molecules (carrier for ATP, NAD and CoA). Smaller solutes with molecular masses below 300–400 Da, like the organic acids malate, oxaloacetate, and 2-oxoglutarate, are shuttled via non-selective channels across the peroxisomal membrane. In comparison to yeast, human, mammals and other eukaryotes, the function of these known peroxisomal transporters and channels in plants are discussed in this review.

Angiosperms integrate a multitude of endogenous and environmental signals to control floral development, thereby ensuring reproductive success. Here, we report the identification of AGAMOUS AND TERMINAL FLOWER (AGTFL), a novel regulator of floral development in Medicago truncatula. Mutation of AGTFL led to the transformation of carpels and stamens into numerous sepals and petals and altered primary inflorescence identity. AGTFL encodes a nucleus‐localized protein containing a putative Myb/SANT‐like DNA‐binding domain and a PKc kinase domain. Molecular and genetic analyses revealed that AGTFL regulates the transcription of MtAGs and MtTFL1 to control floral organ identity and inflorescence development.

Polyamines are small aliphatic amines found in almost all organisms, ranging from bacteria to plants and animals. In most plants, putrescine, the metabolic precursor for longer polyamines, such as spermidine and spermine, is produced from arginine, with either agmatine or ornithine as intermediates. Here we show that Arabidopsis thaliana (Arabidopsis) arginine decarboxylase 1 (ADC1), one of the two known arginine decarboxylases in Arabidopsis, not only synthesizes agmatine from arginine, but also converts N^δ‐acetylornithine to N‐acetylputrescine. Phylogenetic analyses indicate that duplication and neofunctionalization of ADC1 and NATA1, the enzymes that synthesize N^δ‐acetylornithine in Arabidopsis, co‐occur in a small number of related species in the Brassicaceae. Unlike ADC2, which is localized in the chloroplasts, ADC1 is in the endoplasmic reticulum together with NATA1, an indication that these two enzymes have access to the same substrate pool. Together, these results are consistent with a model whereby NATA1 and ADC1 together provide a pathway for the synthesis of N‐acetylputrescine in Arabidopsis.

Maize (Zea mays L.) is a monoecious grass plant in which mature male and female florets form the tassel and ear, respectively. Maize is often used as a model plant to study flower development. Several maize tassel seed mutants, such as the recessive mutants tasselseed1 (ts1) and tasselseed2 (ts2), exhibit a reversal in sex determination, which leads to the generation of seeds in tassels. The phenotype of the dominant mutant, Tasselseed5 (Ts5), is similar to that of ts2. Here, we positionally cloned the underlying gene of Ts5 and characterized its function. We show that the GRMZM2G177668 gene is overexpressed in Ts5. This gene encodes a cytochrome C oxidase, which catalyzes the transformation of jasmonoyl‐L‐isoleucine (JA‐Ile) to 12OH‐JA‐Ile during jasmonic acid catabolism. Consistent with this finding, no JA‐Ile peak was detected in Ts5 tassels during the sex determination period, unlike in the wild type. Transgenic maize plants overexpressing GRMZM2G177668 exhibited a tassel‐seed phenotype similar to that of Ts5. These results indicate that the JA‐Ile peak in tassels is critical for sex determination and that the Ts5 mutant phenotype results from the disruption of this peak in tassels during sex determination.

In higher plants, lateral organs are usually of determinate growth. It remains largely elusive how the determinate growth is achieved and maintained. Previous reports have shown that Arabidopsis PEAPOD (PPD) proteins suppress proliferation of dispersed meristematic cells partly through a TOPLESS corepressor complex. Here, we identified a new PPD‐interacting partner, LIKE HETEROCHROMATIN PROTEIN1 (LHP1), using the yeast two‐hybrid system, and their interaction is mediated by the chromo shadow domain and the Jas domain in LHP1 and PPD2, respectively. Our genetic data demonstrate that the phenotype of ppd2 lhp1 is more similar to lhp1 than to ppd2 , indicating epistasis of lhp1 to ppd2 . Microarray analysis reveals that PPD2 and LHP1 can regulate expression of a common set of genes directly or indirectly. Consistently, chromatin immunoprecipitation results confirm that PPD2 and LHP1 are coenriched at the promoter region of their targets such as D3‐TYPE CYCLINS and HIGH MOBILITY GROUP A , which are upregulated in ppd2, lhp1 and ppd2 lhp1 mutants, and that PPD s mediate repressive histone 3 lysine‐27 trimethylation at these loci. Taken together, our data provide evidence that PPD and LHP1 form a corepressor complex that regulates lateral organ growth.

Mitochondria, the main energy transducers in plant cells, require the proper assembly of respiratory chain complexes I–V for their function. The NADH dehydrogenase 4 (nad4) gene encodes mitochondrial respiratory chain complex I subunit IV, but the mechanism underlying nad4 transcript splicing is unclear. Here, we report that the P‐type pentatricopeptide repeat (PPR) protein DEFECTIVE KERNEL 43 (DEK43) is responsible for cis‐splicing of the nad4 transcript in maize. We demonstrate that DEK43 localizes to both the nucleus and mitochondria. The mutation of Dek43 resulted in embryo‐lethal and light‐colored defective kernels. Among the 22 mitochondrial group II introns, the splicing efficiency of nad4 introns 1 and 3 was reduced by up to 50% compared to the wild type. The levels of complex I and supercomplex I+III₂ were also reduced in dek43. Furthermore, in‐gel NADH dehydrogenase assays indicated that the activities of these complexes were significantly reduced in dek43. Further, the mitochondrial ultrastructure was altered in the mutant. Together, our findings indicate that DEK43, a dual‐localized PPR protein, plays an important role in maintaining mitochondrial function and maize kernel development.

Grain size is a major determinant of cereal grain yields; however, the relevant regulatory mechanisms controlling this trait have not been fully elucidated. The rice (Oryza sativa ) mutant short grain6 (sg6 ) was identified based on its reduced grain length and weight. Here, we functionally characterized the role of SG6 in determining grain size through the regulation of spikelet hull cell division. SG6 encodes a previously uncharacterized plant AT‐rich sequence and zinc‐binding (PLATZ) protein that is ubiquitously localized throughout the cell and is preferentially expressed in the early developing panicles but not in the endosperm. The overexpression of SG6 resulted in significantly larger and heavier grains, as well as increased plant heights, which is consistent with its elevated spikelet hull cell division rate. Yeast two‐hybrid analyses revealed that SG6 interacts with the core cell cycle machinery DP protein and several other putative cell division regulators, consistent with our transcriptomic analysis, which showed that SG6 activates the expression of many DNA replication and cell‐cycle‐related genes. These results confirm the crucial role of SG6 in determining grain size by regulating spikelet hull cell division and provide clues for understanding the functions of PLATZ family proteins and the network regulating cereal grain size.

The DII auxin sensor has been an invaluable tool for mapping the spatiotemporal auxin response and distribution in the model plant Arabidopsis thaliana. The DII sensor and the mDII control sensor are driven by the widely used constitutive 35S promoter. Recently, however, the reliability of the DII sensor has been questioned (Bhatia et al. 2019). They argued that the 35S promoter activity is biased toward leaf primordium adaxial side that face the shoot apical meristem (SAM). Here, we provide additional evidence to show that the mDII control sensor is indeed uniformly distributed in early leaf primordia, in agreement with the original reports (Vernoux et al. 2011; Brunoud et al. 2012). We used the DII/mDII and RPS5A promoter‐driven R2D2 sensors to confirm the presence of asymmetric auxin signaling in early leaf primordia. In addition to these analyses, we show that the imaging data reported by Bhatia et al. (2019) may suffer from artefacts, and that their analysis was artificially biased due to an arbitrary domain demarcation.

The root system of a tree can often extend many‐fold the diameter of the tree; it provides physical support, dissolved minerals and water but relies on a constant supply of nutrients from photosynthetically active tissues in aboveground organs. The phloem is responsible for such transport and the success of a plant relies heavily on the integrity of the phloem in its root system.

This commentary highlights the recent two studies which uncovered dynamic maize kernel RNA‐seq transcriptomes from early seed development, storage filling to maturation, day by day, hour by hour. These two studies provide a ‘maize kernel gene expression dictionary’ that will be powerful for the future studies in seed biology.

The thermosensitive genic male sterile 5 (tms5 ) mutation causes thermosensitive genic male sterility in rice (Oryza sativa ) through loss of RNase Z^S1 function, which influences ubiquitin fusion ribosomal protein L40 (Ub _L40 ) messenger RNA levels during male development. Here, we used ATAC‐seq, combined with analysis of H3K9ac and H3K4me2, to identify changes in accessible chromatin during fertility conversion of the two‐line hybrid rice Wuxiang S (WXS) derived from a mutant tms5 allele. Furthermore, RNA‐seq and bioinformatic analyses identified specific transcription factors (TFs) in differentially accessible chromatin regions. Among these TFs, only GATA10 targeted Ub _L40 . Osgata10 knockout mutations, which resulted in low expression of Ub _L40 and a tendency toward male fertility, confirmed that GATA10 regulated fertility conversion via the modulation of Ub _L40 . Meanwhile, GATA10 acted as a mediator for interactions with ERF65, which revealed that transcriptional regulation is a complex process involving multiple complexes of TFs, namely TF modules. It appears that the ERF141/MADS7/MADS50/MYB modules affect metabolic processes that control anther and pollen development, especially cell wall formation. Our analysis revealed that these modules directly or indirectly affect metabolic pathway‐related genes to coordinate plant growth with proper anther development, and furthermore, that GATA10 regulates fertility conversion via the modulation of Ub _L40 expression.

The endoplasmic reticulum (ER) is the major site for protein folding in eukaryotic cells. ER homeostasis is essential for the development of an organism, whereby the unfolded protein response (UPR) within the ER is precisely regulated. ER‐phagy is a newly identified selective autophagic pathway for removal of misfolded or unfolded proteins within the ER in mammalian cells. Sec62, a component of the translocon complex, was recently characterized as an ER‐phagy receptor during the ER stress recovery phase in mammals. In this study, we demonstrated that the Arabidopsis Sec62 (AtSec62) is required for plant development and might function as an ER‐phagy receptor in plants. We showed that AtSec62 is an ER‐localized membrane protein with three transmembrane domains (TMDs) with its C‐terminus facing to the ER lumen. AtSec62 is required for plant development because atsec62 mutants display impaired vegetative growth, abnormal pollen and decreased fertility. atsec62 mutants are sensitive towards tunicamycin (TM)‐induced ER stress, whereas overexpression of AtSec62 subsequently enhances stress tolerance during the ER stress recovery phase. Moreover, YFP‐AtSec62 colocalizes with the autophagosome marker mCh‐Atg8e in ring‐like structures upon ER stress induction. Taken together, these data provide evidence for the pivotal roles of AtSec62 in plant development and ER‐phagy.

Maize (Zea mays ssp. mays) is a major staple crop, with the highest tonnage among cereal crops worldwide (FAO 2014). Over the past century, maize yields have increased over eight folds in the US central Corn Belt (from 1287 kg ha^-1 in the 1930s to 11,084 kg ha^-1 in 2017, http://www.fao.org, Duvick 2005b) due to a combination of genetic gain resulting from breeding efforts and improved management practices (such as application of synthetic nitrogen fertilizers, weed and pest control, increased efficiency of harvest equipment, etc.). A major management practice that contributed to the continuous yield increase is continual increases in planting density (from 30,000 plant ha^-1 or less in the 1930s to 80,000 plants ha^-1 or higher in the 1980s, Duvick 2005a, 2005b).

Pollen grains are covered by exine that protects the pollen from stress and facilitates pollination. Here we isolated a male sterile mutant s13283 in rice exhibiting aborted pollen with abnormal exine and defective aperture. The mutant gene encodes a novel plasma membrane‐localized legume‐lectin receptor kinase that we named OsLecRK‐S.7. OsLecRK‐S.7 was expressed at different levels in all tested tissues and throughout anther development. In vitro kinase assay showed OsLecRK‐S.7 capable of autophosporylation. Mutation in s13283 (E560K) and mutation of the conserved ATP binding site (K418E) both knocked out the kinase activity. Mass spectrometry showed Thr₃₇₆, Ser₃₇₈, Thr₃₈₆, Thr₄₀₃, and Thr₆₅₇ to be the autophosphorylation sites. Mutation of individual autophosphorylation site affected the in vitro kinase activity to different degrees, but did not abolish the gene function in fertility complementation. oslecrk‐s.7 mutant plant overexpressing OsLecRK‐S.7 recovered male fertility but showed severe growth retardation with reduced number of tillers, and these phenotypes were abolished by E560K or K418E mutation. The results indicated that OsLecRK‐S.7 was a key regulator of pollen development.

Large‐scale production of male sterile seeds can be achieved by introducing a fertility‐restoration gene linked with a pollen‐killer gene into a recessive male sterile mutant. We attempted to construct this system in rice by using a late‐stage pollen‐specific (LSP ) promoter driving the expression of maize α‐amylase gene ZM‐AA1 . To obtain such promoters in rice, we conducted comparative RNA‐seq analysis of mature pollen with meiosis anther, and compared this with the transcriptomic data of various tissues in the Rice Expression Database, resulting in 269 candidate LSP genes. Initial test of nine LSP genes showed that only the most active OsLSP3 promoter could drive ZM‐AA1 to disrupt pollen. We then analyzed an additional 22 LSP genes and found 12 genes stronger than OsLSP3 in late‐stage anthers. The promoters of OsLSP5 and OsLSP6 showing higher expression than OsLSP3 at stages 11 and 12 could drive ZM‐AA1 to inactivate pollen, while the promoter of OsLSP4 showing higher expression at stage 12 only could not drive ZM‐AA1 to disrupt pollen, suggesting that strong promoter activity at stage 11 was critical for pollen inactivation. The strong pollen‐specific promoters identified in this study provided valuable tools for genetic engineering of rice male sterile system for hybrid rice production.

Self‐incompatibility (SI) is a genetic mechanism that rejects self‐pollen and thus prevents inbreeding in some hermaphroditic angiosperms. In the Brassicaceae, SI involves a pollen‐stigma recognition system controlled by a single locus known as the S locus, which consists of two highly polymorphic genes that encode S‐locus cysteine‐rich protein (SCR) and S‐receptor kinase (SRK). When self‐pollen lands on the stigma, the S‐haplotype‐specific interaction between SCR and SRK triggers SI. Here, we show that the GATA transcription factor BnA5.ZML1 suppresses SI responses in Brassica napus and is induced after compatible pollination. The loss‐of‐function mutant bna5.zml1 displays reduced self‐compatibility. In contrast, overexpression of BnA5.ZML1 in self‐incompatible stigmas leads to a partial breakdown of SI responses, suggesting that BnA5.ZML1 is a stigmatic compatibility factor. Furthermore, the expression levels of SRK and ARC1 are up‐regulated in bna5.zml1 mutants, and they are down‐regulated in BnA5.ZML1 overexpressing lines. SRK affects the cellular localization of BnA5.ZML1 through direct protein–protein interaction. Overall, our findings highlight the fundamental role of BnA5.ZML1 in SI responses in B. napus , establishing a direct interaction between BnA5.ZML1 and SRK in this process.

Pollen exine contains complex biopolymers of aliphatic lipids and phenolics. Abnormal development of pollen exine often leads to plant sterility. Molecular mechanisms regulating exine formation have been studied extensively but remain ambiguous. Here we report the analyses of three GDSL esterase/lipase protein genes, OsGELP34, OsGELP110, and OsGELP115, for rice exine formation. OsGELP34 was identified by cloning of a male sterile mutant gene. OsGELP34 encodes an endoplasmic reticulum protein and was mainly expressed in anthers during pollen exine formation. osgelp34 mutant displayed abnormal exine and altered expression of a number of key genes required for pollen development. OsGELP110 was previously identified as a gene differentially expressed in meiotic anthers. OsGELP110 was most homologous to OsGELP115, and the two genes showed similar gene expression patterns. Both OsGELP110 and OsGELP115 proteins were localized in peroxisomes. Individual knockout of OsGELP110 and OsGELP115 did not affect the plant fertility, but double knockout of both genes altered the exine structure and rendered the plant male sterile. OsGELP34 is distant from OsGELP110 and OsGELP115 in sequence, and osgelp34 and osgelp110/osgelp115 mutants were different in anther morphology despite both were male sterile. These results suggested that OsGELP34 and OsGELP110/OsGELP115 catalyze different compounds for pollen exine development.

Water transport from roots to leaves through xylem is important for plant growth and development. Defects in water transport can cause drought stress, even when there is adequate water in the soil. Here, we identified the maize (Zea mays) wilty5 (wi5) mutant, which exhibits marked dwarfing and leaf wilting throughout most of its life cycle under normal growth conditions. wilty5 seedlings exhibited lower xylem conductivity and wilted more rapidly under drought, NaCl, and high temperature treatments than wild‐type plants. Map‐based cloning revealed that WI5 encodes an active endo‐1,4‐β‐xylanase from glycosyl dehydration family 10, which mainly functions in degrading and reorganizing cell wall xylan. Reverse‐transcription polymerase chain reaction and β‐glucuronidase assays revealed that WI5 is highly expressed in stems, especially in internodes undergoing secondary wall assembly. RNA sequencing suggested that WI5 plays a unique role in internode growth. Immunohistochemistry and electron microscopy confirmed that wi5 is defective in xylan deposition and secondary cell wall thickening. Lignin deposition and xylan content were markedly reduced in wi5 compared to the wild‐type plants. Our results suggest that WI5 functions in xylem cell wall thickening through its xylanase activity and thereby regulates xylem water transport, the drought stress response, and plant growth in maize.

Most eukaryotic cells are polarized. Common toolbox regulating cell polarization includes Rho guanosine triphosphatases (GTPases), in which spatiotemporal activation is regulated by a plethora of regulators. Rho of plants (ROPs) are the only Rho GTPases in plants. Although vesicular trafficking was hinted in the regulation of ROPs, it was unclear where vesicle‐carried ROP starts, whether it is dynamically regulated, and which components participate in vesicle‐mediated ROP targeting. In addition, although vesicle trafficking and guanine nucleotide inhibitor (GDI) pathways in Rho signaling have been extensively studied in yeast, it is unknown whether the two pathways interplay. Unclear are also cellular and developmental consequences of their interaction in multicellular organisms. Here, we show that the dynamic targeting of ROP through vesicles requires coat protein complex II and ADP‐ribosylation factor 1‐mediated post‐Golgi trafficking. Trafficking of vesicle‐carried ROPs between the plasma membrane and the trans‐Golgi network is mediated through adaptor protein 1 and sterol‐mediated endocytosis. Finally, we show that GDI and vesicle trafficking synergistically regulate cell polarization and ROP targeting, suggesting that the establishment and maintenance of cell polarity is regulated by an evolutionarily conserved mechanism.

Imitation Switch (ISWI) chromatin remodelers are known to function in diverse multi‐subunit complexes in yeast and animals. However, the constitution and function of ISWI complexes in Arabidopsis thaliana remain unclear. In this study, we identified forkhead‐associated domain 2 (FHA2) as a plant‐specific subunit of an ISWI chromatin‐remodeling complex in Arabidopsis. By in vivo and in vitro analyses, we demonstrated that FHA2 directly binds to RLT1 and RLT2, two redundant subunits of the ISWI complex in Arabidopsis. The stamen filament is shorter in the fha2 and rlt1/2 mutants than in the wild type, whereas their pistil lengths are comparable. The shorter filament, which is due to reduced cell size, results in insufficient pollination and reduced fertility. The rlt1/2 mutant shows an early‐flowering phenotype, whereas the phenotype is not shared by the fha2 mutant. Consistent with the functional specificity of FHA2, our RNA‐seq analysis indicated that the fha2 mutant affects a subset of RLT1/2‐regulated genes that does not include genes involved in the regulation of flowering time. This study demonstrates that FHA2 functions as a previously uncharacterized subunit of the Arabidopsis ISWI complex and is exclusively involved in regulating stamen development and plant fertility.

Plant cells have a powerful capacity in their propagation to adapt to environmental change, given that a single plant cell can give rise to a whole plant via somatic embryogenesis without the need for fertilization. The reprogramming of somatic cells into totipotent cells is a critical step in somatic embryogenesis. This process can be induced by stimuli such as plant hormones, transcriptional regulators and stress. Here, we review current knowledge on how the identity of totipotent cells is determined and the stimuli required for reprogramming of somatic cells into totipotent cells. We highlight key molecular regulators and associated networks that control cell fate transition from somatic to totipotent cells. Finally, we pose several outstanding questions that should be addressed to enhance our understanding of the mechanisms underlying plant cell totipotency.

The polar growth of pollen tubes is essential for the delivery of sperm cells during fertilization in angiosperms. How this polar growth is regulated has been a long‐standing question. An in vitro pharmacological assay previously implicated proton flux in pollen tube growth, although genetic and cellular supporting evidence was lacking. Here, we report that protons form a gradient from the pollen tube tip to the shank region and this gradient is generated by three members of Arabidopsis H⁺‐ATPases (AHAs). Genetic analysis suggested that these AHAs are essential for pollen tube growth, thus providing new insight into the regulation of polar growth.

The shape of comparable tissues and organs is consistent among individuals of a given species, but how this consistency or robustness is achieved remains an open question. The interaction between morphogenetic factors determines organ formation and subsequent shaping, which is ultimately a mechanical process. Using a computational approach, we show that the epidermal layer is essential for the robustness of organ geometry control. Specifically, proper epidermal restriction allows organ asymmetry maintenance, and the tensile epidermal layer is sufficient to suppress local variability in growth, leading to shape robustness. The model explains the enhanced organ shape variations in epidermal mutant plants. In addition, differences in the patterns of epidermal restriction may underlie the initial establishment of organ asymmetry. Our results show that epidermal restriction can answer the longstanding question of how cellular growth noise is averaged to produce precise organ shapes, and the findings also shed light on organ asymmetry establishment.

As sessile organisms, plants perceive, respond, and adapt to the environmental changes for optimal growth and survival. The plant growth and fitness are enhanced by circadian clocks through coordination of numerous biological events. In legume species, nitrogen‐fixing root nodules were developed as the plant organs specialized for symbiotic transfer of nitrogen between microsymbiont and host. Here, we report that the endogenous circadian rhythm in nodules is regulated by MtLHY in legume species Medicago truncatula. Loss of function of MtLHY leads to a reduction in the number of nodules formed, resulting in a diminished ability to assimilate nitrogen. The operation of the 24‐h rhythm in shoot is further influenced by the availability of nitrogen produced by the nodules, leading to the irregulated nyctinastic leaf movement and reduced biomass in mtlhy mutants. These data shed new light on the roles of MtLHY in the orchestration of circadian oscillator in nodules and shoots, which provides a mechanistic link between nodulation, nitrogen assimilation, and clock function.

Plant interphase cortical microtubules (cMTs) mediate anisotropic cell expansion in response to environmental and developmental cues. In Arabidopsis thaliana, KATANIN 1 (KTN1), the p60 catalytic subunit of the conserved MT‐severing enzyme katanin, is essential for cMT ordering and anisotropic cell expansion. However, the regulation of KTN1‐mediated cMT severing and ordering remains unclear. In this work, we report that the Arabidopsis IQ67 DOMAIN (IQD) family gene ABNORMAL SHOOT 6 (ABS6) encodes a MT‐associated protein. Overexpression of ABS6 leads to elongated cotyledons, directional pavement cell expansion, and highly ordered transverse cMT arrays. Genetic suppressor analysis revealed that ABS6‐mediated cMT ordering is dependent on KTN1 and SHADE AVOIDANCE 4 (SAV4). Live imaging of cMT dynamics showed that both ABS6 and SAV4 function as positive regulators of cMT severing. Furthermore, ABS6 directly interacts with KTN1 and SAV4 and promotes their recruitment to the cMTs. Finally, analysis of loss‐of‐function mutant combinations showed that ABS6, SAV4, and KTN1 work together to ensure the robust ethylene response in the apical hook of dark‐grown seedlings. Together, our findings establish ABS6 and SAV4 as positive regulators of cMT severing and ordering, and highlight the role of cMT dynamics in fine‐tuning differential growth in plants.

Although the essential role of messenger RNA methylation in the nucleus is increasingly understood, the nature of ribosomal RNA (rRNA) methyltransferases and the role of rRNA methylation in chloroplasts remain largely unknown. A recent study revealed that CMAL (for Chloroplast mr aW‐ Like) is a chloroplast‐localized rRNA methyltransferase that is responsible for N4‐methylcytidine (m⁴C) in 16S chloroplast rRNA in Arabidopsis thaliana. In this study, we further examined the role of CMAL in chloroplast biogenesis and function, development, and hormone response. The cmal mutant showed reduced chlorophyll biosynthesis, photosynthetic activity, and growth‐defect phenotypes, including severely stunted stems, fewer siliques, and lower seed yield. The cmal mutant was hypersensitive to chloroplast translation inhibitors, such as lincomycin and erythromycin, indicating that the m⁴C‐methylation defect in the 16S rRNA leads to a reduced translational activity in chloroplasts. Importantly, the stunted stem of the cmal mutant was partially rescued by exogenous gibberellic acid or auxin. The cmal mutant grew poorer than wild type, whereas the CMAL‐overexpressing transgenic Arabidopsis plants grew better than wild type in the presence of abscisic acid. Altogether, these results indicate that CMAL is an indispensable rRNA methyltransferase in chloroplasts and is crucial for chloroplast biogenesis and function, photosynthesis, and hormone response during plant growth and development.

Gametophyte development is a pre‐requisite for plant reproduction and seed yield; therefore, studies of gametophyte development help us understand fundamental biological questions and have potential applications in agriculture. The biogenesis and dynamics of endomembrane compartments are critical for cell survival, and their regulatory mechanisms are just beginning to be revealed. Here, we report that the Arabidopsis thaliana SNARE (soluble N‐ethylmaleimide sensitive factor attachment protein receptor) protein YKT61 is essential for both male and female gametogenesis. By using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9)‐based genome editing, we demonstrated that male and female gametophytes carrying YKT61 loss‐of‐function alleles do not survive. Specifically, loss of YKT61 function resulted in the arrest of male gametophytic development at pollen mitosis I and the degeneration of female gametophytes. A three‐base‐pair deletion in YKT61 in the ykt61‐3 mutant resulted in a single‐amino acid deletion in the longin domain of YKT61; the resulting mutant protein does not interact with multiple SNAREs and showed substantially reduced membrane association, suggesting that the N‐terminal longin domain of YKT61 plays multiple roles in its function. This study demonstrates that Arabidopsis YKT61 is essential for male and female gametogenesis and sets an example for functional characterization of essential genes with the combination of Cas9‐mediated editing and expression from a Cas9‐resistant transgene.

Salicylic acid (SA) plays a crucial role in plant immunity. However, its function in plant development is poorly understood. The quiescent center (QC), which maintains columella stem cells (CSCs) in the root apical meristem and typically exhibits low levels of cell division, is critical for root growth and development. Here, we show that the Arabidopsis thaliana SA overaccumulation mutant constitutively activated cell death 1 (cad1), which exhibits increased cell division in the QC, is rescued by additional mutations in genes encoding the SA biosynthetic enzyme SALICYLIC ACID INDUCTION DEFFICIENT2 (SID2) or the SA receptor NONEXPRESSER OF PR GENES1 (NPR1), indicating that QC cell division in the cad1 mutant is promoted by the NPR1‐dependent SA signaling pathway. The application of exogenous SA also promoted QC cell division in wild‐type plants in a dose‐dependent manner and largely suppressed the expression of genes involved in QC maintenance, including those encoding the APETALA2 (AP2) transcription factors PLETHORA1 (PLT1) and PLT2, as well as the homeodomain transcription factor WUSCHEL‐RELATED HOMEOBOX5 (WOX5). Moreover, we showed that SA promotes reactive oxygen species (ROS) production, which is necessary for the QC cell division phenotype in the cad1 mutant. These results provide insight into the function of SA in QC maintenance.

Study on the regulation of broad‐spectrum resistance is an active area in plant biology. RESISTANCE TO POWDERY MILDEW 8.1 (RPW8.1) is one of a few broad‐spectrum resistance genes triggering the hypersensitive response (HR) to restrict multiple pathogenic infections. To address the question how RPW8.1 signaling is regulated, we performed a genetic screen and tried to identify mutations enhancing RPW8.1‐mediated HR. Here, we provided evidence to connect an annexin protein with RPW8.1‐mediated resistance in Arabidopsis against powdery mildew. We isolated and characterized Arabidopsis b7‐6 mutant. A point mutation in b7‐6 at the At5g12380 locus resulted in an amino acid substitution in ANNEXIN 8 (AtANN8). Loss‐of‐function or RNA‐silencing of AtANN8 led to enhanced expression of RPW8.1, RPW8.1‐dependent necrotic lesions in leaves, and defense against powdery mildew. Conversely, over‐expression of AtANN8 compromised RPW8.1‐mediated disease resistance and cell death. Interestingly, the mutation in AtANN8 enhanced RPW8.1‐triggered H₂O₂. In addition, mutation in AtANN8 led to hypersensitivity to salt stress. Together, our data indicate that AtANN8 is involved in multiple stress signaling pathways and negatively regulates RPW8.1‐mediated resistance against powdery mildew and cell death, thus linking ANNEXIN's function with plant immunity.

Ethylene is a gaseous hormone which plays important roles in both plant growth and development and stress responses. Based on studies in the dicot model plant species Arabidopsis, a linear ethylene signaling pathway has been established, according to which ethylene is perceived by ethylene receptors and transduced through CONSTITUTIVE TRIPLE RESPONSE 1 (CTR1) and ETHYLENE‐INSENSITIVE 2 (EIN2) to activate transcriptional reprogramming. In addition to this canonical signaling pathway, an alternative ethylene receptor‐mediated phosphor‐relay pathway has also been proposed to participate in ethylene signaling. In contrast to Arabidopsis, rice, a monocot, grows in semiaquatic environments and has a distinct plant structure. Several novel regulators and/or mechanisms of the rice ethylene signaling pathway have recently been identified, indicating that the ethylene signaling pathway in rice has its own unique features. In this review, we summarize the latest progress and compare the conserved and divergent aspects of the ethylene signaling pathway between Arabidopsis and rice. The crosstalk between ethylene and other plant hormones is also reviewed. Finally, we discuss how ethylene regulates plant growth, stress responses and agronomic traits. These analyses should help expand our knowledge of the ethylene signaling mechanism and could further be applied for agricultural purposes.

Nitrate is the main source of nitrogen for plants but often distributed heterogeneously in soil. Plants have evolved sophisticated strategies to achieve adequate nitrate by modulating the root system architecture. The nitrate acquisition system is triggered by the short mobile peptides C‐TERMINALLY ENCODED PEPTIDES (CEPs) that are synthesized on the nitrate‐starved roots, but induce the expression of nitrate transporters on the other nitrate‐rich roots through an unclear signal transduction pathway. Here, we demonstrate that the transcription factors HBI1 and TCP20 play important roles in plant growth and development in response to fluctuating nitrate supply. HBI1 physically interacts with TCP20, and this interaction was enhanced by the nitrate starvation. HBI1 and TCP20 directly bind to the promoters of CEPs and cooperatively induce their expression. Mutation in HBIs and/or TCP20 resulted in impaired systemic nitrate acquisition response. Our solid genetic and molecular evidence strongly indicate that the HBI1‐TCP20 module positively regulates the CEPs‐mediated systemic nitrate acquisition.