Crop 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.
Cell division is precisely regulated and highly tissue‐specific; studies have suggested that diverse signals in the epidermis, especially the epidermal brassinosteroids (BRs), can regulate root growth. However, the underlying molecular mechanisms that integrate hormonal cues such as BR signaling with other endogenous, tissue‐specific developmental programs to regulate epidermal cell proliferation remain unclear. In this study, we used molecular and biochemical approaches, microscopic imaging and genetic analysis to investigate the function and mechanisms of a P‐type cyclin in root growth regulation. We found that CYCP3;1, specifically expressed in the root meristem epidermis and lateral root cap, can regulate meristem cell division. Mitotic analyses and biochemical studies demonstrated that CYCP3;1 promotes cell division at the G2‐M duration by associating and activating cyclin‐dependent kinase B2‐1 (CDKB2;1). Furthermore, we found that CYCP3;1 expression was inhibited by BR signaling through BRI1‐EMS‐SUPPRESSOR1 (BES1), a positive downstream transcription factor in the BR signaling pathway. These findings not only provide a mechanism of how root epidermal‐specific regulators modulate root growth, but also reveal why the excess of BRs or enhanced BR signaling inhibits cell division in the meristem to negatively regulate root growth.
Breeding of rice varieties that are enriched with essential micronutrients and simultaneously have reduced levels of toxic elements in grains is largely unexplored in rice breeding practice. In this issue of JIPB, Liu et al. (2020) developed two rice lines with a low level of cadmium and simultaneously high levels of zinc or selenium accumulation in the grains, thus providing elite genetic materials for breeding rice varieties that are important for addressing mineral malnutrition and ensuring food safety.
Phosphate starvation leads to a strong reduction in shoot growth and yield in crops. The reduced shoot growth is caused by extensive gene expression reprogramming triggered by phosphate deficiency, which is not itself a direct consequence of low levels of shoot phosphorus. However, how phosphate starvation inhibits shoot growth in rice is still unclear. In this study, we determined the role of OsCYCP4s in the regulation of shoot growth in response to phosphate starvation in rice. We demonstrate that the expression levels of OsCYCP4s , except OsCYCP4;3 , were induced by phosphate starvation. Overexpression of the phosphate starvation induced OsCYCP4s could compete with the other cyclins for the binding with cyclin‐dependent kinases, therefore suppressing growth by reducing cell proliferation. The phosphate starvation induced growth inhibition in the loss‐of‐function mutants cycp4;1 , cycp4;2 , and cycp4;4 is partially compromised. Furthermore, the expression of some phosphate starvation inducible genes is negatively modulated by these cyclins, which indicates that these OsCYCP4s may also be involved in phosphate starvation signaling. We conclude that phosphate starvation induced OsCYCP4s might coordinate phosphate starvation signaling and cell cycle progression under phosphate starvation stress.
The percentage of amylose in the endosperm of rice (Oryza sativa ) largely determines grain cooking and eating qualities. Granule‐bound starch synthase I (GBSSI) and GBSSII are responsible for amylose biosynthesis in the endosperm and leaf, respectively. Here, we identified OsGBP , a rice GBSS‐binding protein that interacted with GBSSI and GBSSII in vitro and in vivo . The total starch and amylose contents in osgbp mutants were significantly lower than those of wild type in leaves and grains, resulting in reduced grain weight and quality. The carbohydrate‐binding module 48 (CBM48) domain present in the C‐terminus of OsGBP is crucial for OsGBP binding to starch. In the osgbp mutant, the extent of GBSSI and GBSSII binding to starch in the leaf and endosperm was significantly lower than wild type. Our data suggest that OsGBP plays an important role in leaf and endosperm starch biosynthesis by mediating the binding of GBSS proteins to developing starch granules. This elucidation of the function of OsGBP enhances our understanding of the molecular basis of starch biosynthesis in rice and contributes information that can be potentially used for the genetic improvement of yield and grain quality.
Crop yield is sensitive to salt stresses, for which Calcineurin B‐like proteins (CBLs) are major response factors. This study shows that Arabidopsis CBL10, through protein S ‐acylation by protein S ‐acyl transferase10, targets to the vacuolar membrane to confer salt tolerance.
Hybrid rice proved to be high‐yielding and is of great importance to food safety worldwide. By using gene editing techniques, we generated one‐line hybrid rice by preventing meiosis from occurring, which can largely contribute to maintaining the hybrid dominance.
High amylose starch can be produced by plants deficient in the function of branching enzymes (BEs). Here we report the production of transgenic cassava (Manihot esculenta Crantz) with starches containing up to 50% amylose due to the constitutive expression of hair‐pin dsRNAs targeting the BE1 or BE2 genes. All BE1‐RNAi plant lines (BE1i) and BE2‐RNAi plant lines (BE2i) were grown up in the field, but with reduced total biomass production. Considerably high amylose content in the storage roots of BE2i plant lines was achieved. Storage starch granules of BE1i and BE2i plants had similar morphology as wild type (WT), however, the size of BE1i starch granules were bigger than that of WT. Comparisons of amylograms and thermograms of all three sources of storage starches revealed dramatic changes to the pasting properties and a higher melting temperature for BE2i starches. Glucan chain length distribution analysis showed a slight increase in chains of DP>36 in BE1i lines and a dramatic increase in glucan chains between DP 10‐20 and DP>40 in BE2i lines. Furthermore, BE2i starches displayed a B‐type X‐ray diffraction pattern instead of the A‐type pattern found in BE1i and WT starches. Therefore, cassava BE1 and BE2 function differently in storage root starch biosynthesis.
Auxin is a crucial phytohormone, controlling multiple aspects of plant growth and responses to the changing environment. However, the role of local auxin biosynthesis in specific developmental programs remains unknown in crops. This study characterized the rice tillering and small grain 1 (tsg1) mutant, which has more tillers but a smaller panicle and grain size resulting from a reduction in endogenous auxin. TSG1 encodes a tryptophan aminotransferase that is allelic to the FISH BONE (FIB) gene. The tsg1 mutant showed hypersensitivity to indole‐3‐acetic acid and the competitive inhibitor of aminotransferase, L‐kynurenine. TSG1 knockout resulted in an increased tiller number but reduction in grain number and size, and decrease in height. Meanwhile, deletion of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 caused no obvious changes, although the phenotype of the TSG1/OsTAR1 double mutant was intensified and infertile, suggesting gene redundancy in the rice tryptophan aminotransferase family. Interestingly, TSG1 and OsTAR1, but not OsTARL1 and OsTARL2, displayed marked aminotransferase activity. Meanwhile, subcellular localization was identified as the endoplasmic reticulum, while phylogenetic analysis revealed functional divergence of TSG1 and OsTAR1 from OsTARL1 and OsTARL2. These findings suggest that TSG1 dominates the tryptophan aminotransferase family, playing a prominent role in local auxin biosynthesis in rice.
Rice (Oryza sativa) is one of the most widely cultivated food crops, worldwide. Tissue culture is extensively used in rice breeding and functional genome research. The ability to induce callus determines whether a particular rice variety can be subjected to tissue culture and Agrobacterium‐mediated transformation. Over the past two decades, many quantitative trait loci (QTLs) related to callus induction traits have been identified; however, individual genes associated with rice callus induction have not been reported. In this study, we characterized three callus‐induction traits in a global collection of 510 rice accessions. A genome‐wide association study of the rice population in its entirety as well as subpopulations revealed 21 significant loci located in rice callus induction QTLs. We identified three candidate callus induction genes, namely CRL1, OsBMM1, and OsSET1, which are orthologs of Arabidopsis LBD17/LBD29, BBM, and SWN, respectively, which are known to affect callus formation. Furthermore, we predicted that 14 candidate genes might be involved in rice callus induction and showed that RNA interference (RNAi)‐mediated disruption of OsIAA10 inhibited callus formation on tissue culture medium. Embryo growth in the OsIAA10 RNAi line was not inhibited by synthetic auxin (2,4‐D) treatment, suggesting that OsIAA10 may perceive auxin and activate the expression of downstream genes, such as CRL1, to induce callus formation. The significant loci and candidate genes identified here may provide insight into the mechanism underlying callus formation in rice.
Grain size is an important determinant of yield potential in crops. We previously demonstrated that natural mutations in the regulatory sequences of qSW5/GW5 confer grain width diversity in rice. However, the biological function of a GW5 homolog, named GW5‐Like (GW5L), remains unknown. In this study, we report on GW5L knockout mutants in Kitaake, a japonica cultivar (cv.) considered to have a weak gw5 variant allele that confers shorter and wider grains. GW5L is evenly expressed in various tissues, and its protein product is localized to the plasma membrane. Biochemical assays verified that GW5L functions in a similar fashion to GW5. It positively regulates brassinosteroid (BR) signaling through repression of the phosphorylation activity of GSK2. Genetic data show that GW5L overexpression in either Kitaake or a GW5 knockout line, Kasaorf3 (indica cv. Kasalath background), causes more slender, longer grains relative to the wild‐type. We also show that GW5L could confer salt stress resistance through an association with calmodulin protein OsCaM1‐1. These findings identify GW5L as a negative regulator of both grain size and salt stress tolerance, and provide a potential target for breeders to improve grain yield and salt stress resistance in rice.
Brassinosteroids (BRs) play crucial roles in many aspects of plant development. However, their function in spikelet differentiation and degeneration in rice (Oryza sativa L.) remains unclear. Here, we investigated the roles of these phytohormones in spikelet development in field‐grown rice subjected to five different nitrogen (N) fertilization treatments during panicle differentiation. BR levels and expression of genes involved in BR biosynthesis and signal transduction were measured in spikelets. Pollen fertility and the number of differentiated spikelets were closely associated with 24‐epicastasterone (24‐epiCS) and 28‐homobrassinolide (28‐homoBL) levels in spikelets. Enhanced BR biosynthesis and signal transduction, in response to N treatment, enhanced spikelet differentiation, reduced spikelet degeneration, and increased grain yield. Increases in proton‐pumping ATPase activity, ATP concentration, energy charge, and antioxidant system (AOS) levels were consistent with 24‐epiCS and 28‐homoBL concentrations. Exogenous application of 24‐epiCS or 28‐homoBL on young panicles induced a marked increase in endogenous 24‐epiCS or 28‐homoBL levels, energy charge, AOS levels, spikelet differentiation, and panicle weight. The opposite effects were observed following treatment with a BR biosynthesis inhibitor. Our findings indicate that, in rice, BRs mediate the effects of N fertilization on spikelet development and play a role in promoting spikelet development through increasing AOS levels and energy charge during panicle development.
