N⁶‐methyladenosine (m⁶A) is a prevalent modification in messenger RNAs and circular RNAs that play important roles in regulating various aspects of RNA metabolism. However, the occurrence of the m⁶A modification in plant circular RNAs has not been reported. A widely used method to identify m⁶A modifications relies on m⁶A‐specific antibodies followed by next‐generation sequencing of precipitated RNAs (MeRIP‐Seq). However, one limitation of MeRIP‐Seq is that it does not provide the precise location of m⁶A at single‐nucleotide resolution. Although more recent sequencing techniques such as Nanopore‐based direct RNA sequencing (DRS) can overcome such limitations, the technology does not allow sequencing of circular RNAs, as these molecules lack a poly(A) tail. Here, we developed a novel method to detect the precise location of m⁶A modifications in circular RNAs using Nanopore DRS. We first enriched our samples for circular RNAs, which we then fragmented and sequenced on the Nanopore platform with a customized protocol. Using this method, we identified 470 unique circular RNAs from DRS reads based on the back‐spliced junction region. Among exonic circular RNAs, about 10% contained m⁶A sites, which mainly occurred around acceptor and donor splice sites. This study demonstrates the utility of our antibody‐independent method in identifying total and methylated circular RNAs using Nanopore DRS. This method has the additional advantage of providing the exact location of m⁶A sites at single‐base resolution in circular RNAs or linear transcripts from non‐coding RNA without poly(A) tails.

The juvenile‐to‐adult transition in plants involves changes in vegetative growth and plant architecture; the timing of this transition has important implications for agriculture. The microRNA miR156 regulates this transition and shoot maturation in plants. In Arabidopsis thaliana, deposition of histone H3 trimethylation on lysine 27 (H3K27me3, a repressive mark) at the MIR156A/C loci is regulated by Polycomb Repressive Complex 1 (PRC1) or PRC2, depending on the developmental stage. The levels of miR156 progressively decline during shoot maturation. The amount of H3K27me3 at MIR156A/C loci affects miR156 levels; however, whether this epigenetic regulation is conserved remains unclear. Here, we found that in rice (Oryza sativa), the putative PRC1 subunit LIKE HETEROCHROMATIN PROTEIN 1 (OsLHP1), with the miR156–SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE (SPL) module, affects developmental phase transitions. Loss of OsLHP1 function results in ectopic expression of MIR156B/C/I/E, phenocopy of miR156 overexpression, and reduced H3k27me3 levels at MIR156B/C/I/E. This indicates that OsLHP1 has functionally diverged from Arabidopsis LHP1. Genetic and transcriptome analyses of wild‐type, miR156b/c‐overexpression, and Oslhp1‐2 mutant plants suggest that OsLHP1 acts upstream of miR156 and SPL during the juvenile‐to‐adult transition. Therefore, modifying the OsLHP1–miR156–SPL pathway may enable alteration of the vegetative period and plant architecture.

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.

Flowering time and plant height are key agronomic traits that directly affect soybean (Glycine max) yield. APETALA1 (AP1) functions as a class A gene in the ABCE model for floral organ development, helping to specify carpel, stamen, petal, and sepal identities. There are four AP1 homologs in soybean, all of which are mainly expressed in the shoot apex. Here, we used clustered regularly interspaced short palindromic repeats (CRISPR) – CRISPR‐associated protein 9 technology to generate a homozygous quadruple mutant, gmap1, with loss‐of‐function mutations in all four GmAP1 genes. Under short‐day (SD) conditions, the gmap1 quadruple mutant exhibited delayed flowering, changes in flower morphology, and increased node number and internode length, resulting in plants that were taller than the wild type. Conversely, overexpression of GmAP1a resulted in early flowering and reduced plant height compared to the wild type under SD conditions. The gmap1 mutant and the overexpression lines also exhibited altered expression of several genes related to flowering and gibberellic acid metabolism, thereby providing insight into the role of GmAP1 in the regulatory networks controlling flowering time and plant height in soybean. Increased node number is the trait with the most promise for enhancing soybean pod number and grain yield. Therefore, the mutant alleles of the four AP1 homologs described here will be invaluable for molecular breeding of improved soybean yield.

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.

Cuticular wax is a natural barrier on terrestrial plant organs, which protects plants from damages caused by a variety of stresses. Here, we report the identification and functional characterization of a cuticular‐wax‐related gene, Zea mays L. SEMI‐ROLLED LEAF 5 (ZmSRL5). The loss‐of‐function mutant srl5, which was created by a 3,745 bp insertion in the first intron that led to the premature transcript, exhibited abnormal wax crystal morphology and distribution, which, in turn, caused the pleiotropic phenotypes including increased chlorophyll leaching and water loss rate, decreased leaf temperature, sensitivity to drought, as well as semi‐rolled mature leaves. However, total wax amounts showed no significant difference between wild type and semi‐rolled leaf5 (srl5) mutant. The phenotype of srl5 was confirmed through the generation of two allelic mutants using CRISPR/Cas9. ZmSRL5 encodes a CASPARIAN‐STRIP‐MEMBRANE‐DOMAIN‐LIKE (CASPL) protein located in plasma membrane, and highly expressed in developing leaves. Further analysis showed that the expressions of the most wax related genes were not affected or slightly altered in srl5. This study, thus, primarily uncovers that ZmSRL5 is required for the structure formation of the cuticular wax and could increase the drought tolerance by maintaining the proper cuticular wax structure in maize.

Iron (Fe) deficient plants employ multiple strategies to increase root uptake and root‐to‐shoot translocation of Fe. The identification of genes that are responsible for these processes, and a comprehensive understanding of the regulatory effects of transcriptional networks on their expression, including transcription factors (TFs), is underway in Arabidopsis thaliana. Here, we show that a Histone‐ or heme‐associated proteins (HAP) transcription factor (TF), HAP5A, is necessary for the response to Fe deficiency in Arabidopsis. Its expression was induced under Fe deficiency, and the lack of HAP5A significantly decreased Fe translocation from the root to the shoot, resulting in substantial chlorosis of the newly expanded leaves, compared with the wild‐type (WT, Col‐0). Further analysis found that the expression of a gene encoding nicotianamine (NA) synthase (NAS1) was dramatically decreased in the hap5a mutant, regardless of the Fe status. Yeast‐one‐hybrid and ChIP analyses suggested that HAP5A directly binds to the promoter region of NAS1. Moreover, overexpression of NAS1 could rescue the chlorosis phenotype of hap5a in Fe deficient conditions. In summary, a novel pathway was elucidated, showing that NAS1‐dependent translocation of Fe from the root to the shoot is controlled by HAP5A in Fe‐deficient Arabidopsis thaliana.

Iron is an essential microelement for plant growth. After uptake from the soil, iron is chelated by ligands and translocated from roots to shoots for subsequent utilization. However, the number of ligands involved in iron chelation is unclear. In this study, we identified and demonstrated that GLU1, which encodes a ferredoxin‐dependent glutamate synthase, was involved in iron homeostasis. First, the expression of GLU1 was strongly induced by iron deficiency condition. Second, lesion of GLU1 results in reduced transcription of many iron‐deficiency‐responsive genes in roots and shoots. The mutant plants revealed a decreased iron concentration in the shoots, and displayed severe leaf chlorosis under the condition of Fe limitation, compared to wild‐type. Third, the product of GLU1, glutamate, could chelate iron in vivo and promote iron transportation. Last, we also found that supplementation of glutamate in the medium can alleviate cadmium toxicity in plants. Overall, our results provide evidence that GLU1 is involved in iron homeostasis through affecting glutamate synthesis under iron deficiency conditions in Arabidopsis.

High salinity is one of the major limiting factors that reduces crop productivity and quality. Herein, we report that small SALT TOLERANCE ENHANCER1 (STE1) protein without any known conserved domains is required for tomato salt tolerance. Overexpression (OE) of SlSTE1 enhanced the tolerance to multiple chloride salts (NaCl, KCl, and LiCl) and oxidative stress, along with elevated antioxidant enzyme activities, increased abscisic acid (ABA) and chlorophyll contents, and reduced malondialdehyde (MDA) and reactive oxygen species (ROS) accumulations compared to that of wild‐type (WT) plants. Moreover, decreased K⁺ efflux and increased H⁺ efflux were detected in the OE plants, which induced a higher K⁺/Na⁺ ratio. In contrast, SlSTE1‐RNAi plants displayed decreased tolerance to salt stress. RNA‐seq data revealed 1 330 differentially expressed genes in the OE plants versus WT plants under salt stress, and the transcription of numerous and diverse genes encoding transcription factors, stress‐related proteins, secondary metabolisms, kinases, and hormone synthesis/signaling‐related proteins (notably ABA and 1‐aminocyclopropane‐1‐carboxylate) was greatly elevated. Furthermore, SlSTE1‐OE plants showed increased sensitivity to ABA, and the results suggest that SlSTE1 promotes ABA‐dependent salt stress‐responsive pathways by interacting with SlPYLs and SlSnRK2s. Collectively, our findings reveal that the small SlSTE1 protein confers salt tolerance via ABA signaling and ROS scavenging and improves ion homeostasis in tomato.

The brown planthopper (BPH) and striped stem borer (SSB) are the most devastating insect pests in rice (Oryza sativa ) producing areas. Screening for endogenous resistant genes is the most practical strategy for rice insect‐resistance breeding. Forty‐five mutants showing high resistance against BPH were identified in a rice T‐DNA insertion population (11,000 putative homozygous lines) after 4 years of large‐scale field BPH‐resistance phenotype screening. Detailed analysis showed that deficiency of rice mitochondrial outer membrane protein 64 (OM64 ) gene resulted in increased resistance to BPH. Mitochondrial outer membrane protein 64 protein is located in the outer mitochondrial membrane by subcellular localization and its deficiency constitutively activated hydrogen peroxide (H₂O₂) signaling, which stimulated antibiosis and tolerance to BPH. The om64 mutant also showed enhanced resistance to SSB, a chewing insect, which was due to promotion of Jasmonic acid biosynthesis and related responses. Importantly, om64 plants presented no significant changes in rice yield‐related characters. This study confirmed OM64 as a negative regulator of rice herbivore resistance through regulating H₂O₂ production. Mitochondrial outer membrane protein 64 is a potentially efficient candidate to improve BPH and SSB resistance through gene deletion. Why the om64 mutant was resistant to both piercing‐sucking and chewing insects via a gene deficiency in mitochondria is discussed.

Following double fertilization, plant endosperm nuclei undergo syncytial divisions, followed by synchronous cellularization. Cellularization is a key event during endosperm development, but our understanding of its regulation is limited to Arabidopsis. In this study we show that OsbZIP76 regulates cellularization in rice (Oryza sativa). Activation of OsbZIP76 coincided with the initiation of cellularization, and its knockdown or knockout mutants exhibited precocious cellularization. Genes involved in endosperm development or starch biosynthesis were prematurely activated in the osbzip76 caryopsis. As a putative transcription factor, OsbZIP76 alone lacked transcriptional activation activity; however, it interacted with the nuclear factor Y (NF‐Y) family transcription factors OsNF‐YB9 and OsNF‐YB1 in yeast and in planta. OsbZIP76 and OsNF‐YB9 were predominantly expressed in the endosperm and the proteins colocalized. Seeds of osnf‐yb1 and osbzip76 mutants showed reduced size and reduced apparent amylose content. The parent‐of‐origin‐dependent expression of OsbZIP76 is variable in different rice accessions. In summary, OsbZIP76 is an endosperm‐expressed imprinted gene that regulates endosperm development in rice.

The authors would like to draw the reader's attention to errors in the following article:

Yang K, Wang L, Le J and Dong J (2020) Cell polarity: Regulators and mechanisms in plants. J Integr Plant Biol 62 (1): 132–147. DOI: 10.1111/jipb.12904

The affiliations of Jie Le were incomplete. Jie Le's affiliations should read:

1. Key Laboratory of Plant Molecular Physiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.

2. University of Chinese Academy of Sciences, Beijing 100049, China

The authors apologize to our readers for this mistake.