Role of the Arabidopsis thafiana NAC transcription factors ANAC019 and ANAC055 in regulating jasmonic acid-signaled defense responses

Jasmonic acid （JA） is an important phytohormone that regulates plant defense responses against herbivore attack, pathogen infection and mechanical wounding. In this report, we provided biochemical and genetic evidence to show that the Arabidopsis thaliana NAC family proteins ANAC019 and ANAC055 might function as transcription activators to regulate JA-induced expression of defense genes. The role of the two NAC genes in JA signaling was examined with the anacO19 anac055 double mutant and with transgenic plants overexpressing ANACO19 or ANAC055. The anacO19 anac055 double mutant plants showed attenuated JA-induced VEGETATIVE STORAGE PROTEIN1 （VSP1） and LIPOXYGENASE2 （LOX2） expression, whereas transgenic plants overexpressing the two NAC genes showed enhanced JA-induced VSP1 and LOX2 expression. That the JA-induced expression of the two NAC genes depends on the function of COIl and AtMYC2, together with the finding that overexpression of ANACO19 partially rescued the JA-related phenotype of the atmyc2-2 mutant, has led us to a hypothesis that the two NAC proteins act downstream of AtMYC2 to regulate JA-signaled defense responses. Further evidence to substantiate this idea comes from the observation that the response of the anacO19 anac055 double mutant to a necrotrophic fungus showed high similarity to that of the atmyc2-2 mutant.

OsWRKY78 regulates panicle exsertion via gibberellin signaling pathway in rice

Panicle exsertion is one of the crucial agronomic traits in rice(Oryza sativa).Shortening of panicle exsertion often leads to panicle enclosure and severely reduces seed production.Gibberellin(GA)plays important roles in regulating panicle exsertion.However,the underlying mechanism and the relative regulatory network remain elusive.Here,we characterized the oswrky78 mutant showing severe panicle enclosure,and found that the defect of oswrky78 is caused by decreased bioactive GA contents.Biochemical analysis demonstrates that OsWRKY78 can directly activate GA biosynthesis and indirectly suppress GA metabolism.Moreover,we found OsWRKY78 can interact with and be phosphorylated by mitogen-activated protein kinase(MAPK)kinase OsMAPK6,and this phosphorylation can enhance OsWRKY78 stability and is necessary for its biological function.Taken together,these results not only reveal the critical function of OsWRKY78,but also reveal its mechanism via mediating crosstalk between MAPK and the GA signaling pathway in regulating panicle exsertion.

Grow rice under sunshine of Xizang/Tibet:promise and challenges

Xizang,previously known as Tibet,is located in the southwest region of China and is the highest region of the Qinghai-Tibet Plateau(QzP),with an average altitude of over 4000 m.With the development of modern agriculture,the grain productivity in Xizang has been effectively improved.The total annual grain production has increased from 558,700 tons in 1988 to 1044,000 tons in 2018(Xizang Statistical Year Book).

Oryza sativa mediator subunit OsMED25 interacts with OsBZR1 to regulate brassinosteroid signaling and plant architecture in rice

Brassinosteroids(BRs)are plant-specific steroid hormones which regulate plant growth,development,and adaptation.Transcriptional regulation plays key roles in plant hormone signaling.A mediator can serve as a bridge between gene-specific transcription factors and the RNA polymerase machinery,functioning as an essential component in regulating the transcriptional process.However,whether a mediator is involved in BR signaling is unknown.Here,we discovered that Oryza sativa mediator subunit 25(Os MED25)is an important regulator of rice BR signaling.Phenotypic analyses showed that the Os MED25-RNAi and osmed25 mutant presented erect leaves,as observed in BR-deficient mutants.In addition,the Os MED25-RNAi and osmed25 mutant exhibited decreased BR sensitivity.Genetic analysis indicated that Os MED25-RNAi could suppress the enhanced BR signaling phenotype of Osbzr1-D.Further biochemical analysis showed that Os MED25 interacts with Os BZR1 in vivo,and Os MED25 is enriched on the promoter of Os BZR1 target genes.RNA sequencing analysis indicated that Os MED25 affects the expression of approximately 45%of Os BZR1-regulated genes and mainly functions as a corepressor of Os BZR1.Together,these findings revealed that Os MED25 regulates rice BR signaling by interacting with Os BZR1 and modulating the expression of Os BZR1 target genes,thus expanding our understanding of the roles of mediators in plant hormone signaling.

A Strategy for the Acquisition and Analysis of Image-Based Phenome in Rice during the Whole Growth Period

As one of the most widely grown crops in the world,rice is not only a staple food but also a source of calorie intake for more than half of the world's population,occupying an important position in China's agricultural production.Thus,determining the inner potential connections between the genetic mechanisms and phenotypes of rice using dynamic analyses with high-throughput,nondestructive,and accurate methods based on high-throughput crop phenotyping facilities associated with rice genetics and breeding research is of vital importance.In this work,we developed a strategy for acquiring and analyzing 58 image-based traits(i-traits)during the whole growth period of rice.Up to 84.8%of the phenotypic variance of the rice yield could be explained by these i-traits.A total of 285 putative quantitative trait loci(QTLs)were detected for the i-traits,and principal components analysis was applied on the basis of the i-traits in the temporal and organ dimensions,in combination with a genome-wide association study that also isolated QTLs.Moreover,the differences among the different population structures and breeding regions of rice with regard to its phenotypic traits demonstrated good environmental adaptability,and the crop growth and development model also showed high inosculation in terms of the breeding-region latitude.In summary,the strategy developed here for the acquisition and analysis of image-based rice phenomes can provide a new approach and a different thinking direction for the extraction and analysis of crop phenotypes across the whole growth period and can thus be useful for future genetic improvements in rice.

Combinations of Hd2 and Hd4 genes determine rice adaptability to Heilongjiang Province, northern limit of China

Heading date is a key trait in rice domestication and adaption, and a number of quantitative trait loci（QTLs）have been identified. The rice（Oryza sativa L.） cultivars in the Heilongjiang Province, the northernmost region of China,have to flower extremely early to fulfill their life cycle.However, the critical genes or different gene combinations controlling early flowering in this region have not been determined. QTL and candidate gene analysis revealed that Hd2/Ghd7.1/Os PRR37 plays a major role in controlling rice distribution in Heilongjiang. Further association analysis with a collection of rice cultivars demonstrated that another three major QTL genes（Hd4/Ghd7, Hd5/DTH8/Ghd8, and Hd1）also participate in regulating heading date under natural long day（LD） conditions. Hd2/Ghd7.1/Os PRR37 and Hd4/Ghd7 are two major QTLs and function additively. With the northward rice cultivation, the Hd2/Ghd7.1/Os PRR37 and Hd4/Ghd7 haplotypes became non-functional alleles. Hd1 might be non-functional in most Heilongjiang rice varieties,implying that recessive hd1 were selected during local rice breeding. Non-functional Hd5/DTH8/Ghd8 is very rare, but constitutes a potential target for breeding extremely early flowering cultivars. Our results indicated that diverse genetic combinations of Hd1, Hd2, Hd4, and Hd5 determined the different distribution of rice varieties in this northernmost province of China.

High-efficiency breeding of early-maturing rice cultivars via CRISPR/Cas9-mediated genome editing

Rice is a staple food for more than half of the human population.It has been estimated that by 2030,40%more rice needs to be produced in order to meet the growing demand（Khush,2005）.One of the strategies to improve rice productivity is to enlarge rice growth areas, such as the northward expansion of the growth region in Heilongjiang Province, the northernmost region of China （Li et al., 2015）. However, the northward cultivation is accompanied with daylength extension and temperature decrease, which are unfavor- able for rice, a tropical short-day plant, to complete flowering and seed setting. Thus, the need for early-maturing rice cultivars with extremely low photoperiod sensitivity is urgent.

OsMKKK70 regulates grain size and leaf angle in rice through the OsMKK4-OsMAPK6-OsWRKY53 signaling pathway

Grain size and leaf angle are key agronomic traits that determine final yields in rice.However,the underlying molecular mechanisms are not well understood.Here we demonstrate that the Oryza sativa Mitogen Activated Protein Kinase Kinase Kinase OsMKKK70 regulates grain size and leaf angle in rice.Overexpressing OsMKKK70 caused plants to produce longer seeds.The osmkkk62/70 double mutant and the osmkkk55/62/70 triple mutant displayed significantly smaller seeds and a more erect leaf angle compared to the wild type,indicating that OsMKKK70 functions redundantly with its homologs Os MKKK62 and Os MKKK55.Biochemical analysis demonstrated that OsMKKK70 is an active kinase and that OsMKKK70 interacts with Os MKK4 and promotes Os MAPK6 phosphorylation.In addition,the osmkkk62/70 double mutant showed reduced sensitivity to Brassinosteroids(BRs).Finally,overexpressing constitutively active Os MKK4,Os MAPK6,and Os WRKY53 can partially complement the smaller seed size,erect leaf,and BR hyposensitivity of the osmkkk62/70 double mutant.Taken together,these findings suggest that OsMKKK70 might regulate grain size and leaf angle in rice by activating Os MAPK6 and that OsMKKK70,Os MKK4,Os MAPK6,and Os WRKY53 function in a common signaling pathway that controls grain shape and leaf angle.

bZIP71 delays flowering by suppressing Ehd1 expression in rice

Flowering time is a fundamental factor determining the global distribution and final yield of rice(Oryza sativa).Although diverse flowering time genes have been reported in this crop,the transcriptional regulation of its key flowering genes are poorly understood.Here,we report that a basic leucine zipper transcription factor,bZIP71,functions as a flowering repressor.The overexpression of bZIP71 delays flowering,while the bzip71 mutant flowers early in both long-day and short-day conditions.A genetic analysis showed that the regulation of flowering by bZIP71 might be independent of Heading date 2(Hd2),Hd4,and Hd5.Importantly,bZIP71 directly associates with the Early heading date 1(Ehd1)promoter and represses its transcription,and genetically the function of bZIP71 is impaired in the ehd1 mutant.Moreover,bZIP71 interacts with major components of polycomb repressive complex 2(PRC2),SET domain group protein 711(SDG711),and Fertilization independent endosperm 2(FIE2),through which bZIP71 regulates the H3K27me3 level of Ehd1.Taken together,we present a transcriptional regulatory mechanism in which bZIP71 enhances the H3K27me3 level of Ehd1 and transcriptionally represses its expression,which not only offers a novel insight into a flowering pathway,but also provides a valuable putative target for the genetic engineering and breeding of elite rice cultivars.