Control Of Grain And Organ Size By SLG1 And SLG2 In Rice

In rice,grain size and leaf size are important agronomic traits,which directly affect the production of rice.In plants,organ size is usually determined by two consecutive biological process:cell proliferation and cell expansion.As an endogen model plant,many factors that control grain size and leaf size in rice have been identified,but we know little about the regulatory mechanism and regulation network of these factors.At the early stage of the experiment,the slgl-1,slgl-2 and slg2 mutant were isolated from the japonica variety KYJ mutagenized with EMS,they form the narrow leaves,narrow grains,while overexpression of Slender Leaf and Grain 1(SLG1),Slender Leaf and Grain 2(SLG2)results in large grains,suggesting that both SLG1 and SLG2 act as positive regulators of organ size.This study shows that SLG1 and SLG2 regulate the width of grains and leaves by reducing the cell division rate.SLG1 encodes a kind of mediate complex,SLG2 encodes a kind of histone H3K4 demethylation enzyme,they are located in nucleus.SLG1 and SLG2 are expressed in panicles,grains and leaves,with higher levels in young organs.Genetic analysis and protein interactions results show that SLG1 acts in the same genetic pathways with SLG2 to regulate grain and leaf width.Biochemical experimental results by assay of Co-IP,LUC and yeast two-hybrid show that WUSCHEL-RELATED HOMEOBOX 3A(WOX3A)interacts with SLG1 and SLG2,and genetic analysis demonstrate that WOX3A acts in the same genetic pathway with SLG1 and SLG2,In addition,the EMSA experiment in vitro and CHIP experiment in vivo results show that DROUGHT AND SALT TOLERANCE(DST)directly binds the WOX3A promoter region,represses the expression of WOX3A to regulate the grain and leaf size.The data from the genetic relationship indicates that DST and WOX3A act in a common pathway to regulate grain and leaf width.Overexpression of DST results in small grains,slender leaves and drawf plants,indicating that DST acts as a negative regulator of grain and leaf size.We extracted RNA from seedlings and young panicles,then conducted the quantitative real-time PCR,these results indicate that DST and WOX3A both have feedback regulation effects.Taken together,we identified SLG1 and SLG2 as new grain and organ size regulators,which play important roles in transcription regulation system.SLG1,SLG2 and WOX3A interacts with each other and forms a new transcriptional complex,repressing the expression of the downstream gene DST.Zinc finger protein DST directly binds the WOX3A promoter regions,represses the expression of WOX3A to regulate the grain and leaf size.In addition,DST or WOX3A can represses each other on the transcriptional regulation level.The study enlarges the genetic resources,provides a new theoretical basis for genetic breeding and has discovered new pathways to improve potential yield in rice.