Mining And Functional Analysis Of Two Key Gene Associated With Grain Yield In Rice(Oryza Sativa L.)

Ideal plant architecture has become a significant objective in high yield rice breeding.The important characteristics of the ideal plant architecture(IPA)include:1.ideal plant height;2.low tiller numbers with few unproductive tillers;3.more grains per panicle than the currently cultivated varieties;4.thick and sturdy stems.Plant height is one of the most important agronomic traits for producing high yields.Excessive plant height results in lodging and reduced yield.Rice yields are greatly increased by the use of the semi-dwarf 1(sdl)gene in the initial Green Revolution.It is therefore very important to find alternative semi-dwarf resources,and to identify the genes involved and make them available to breeders.Grain size is determined by grain length,grain width and grain thickness,whichdepend on cell division and expansion.Genes involved in cell cycle and cell expansion take part in these mechanisms.It is very important to find new grain size regulators and make use of it to improve rice grain yield.1 In this study we reported a spontaneous semi-dwarf mutant in indica rice cultivar(cv.)'Kasalath',semi-dwarf Kasalath(sdk).Genetic analysis showed that the dwarf stature is controlled by a new semi-dwarf gene.The main results showed below:1.1 At heading,sdk shows an obvious dwarf phenotype compared to Kasalath.Thepanicle and grain size of sdk is much smaller than Kasalath,but there was no significant difference in No.of tillers per plant and No.of fertile seeds per panicle compared to Kasalath.In contrast to Kasalath,sdk is awnless.All internodes were shorter than those of Kasalath.Electron microscopy of third internodes showed that longitudinal sections of internode cells in sdk were smaller,tightly packed and irregular,explaining the reduced height of sdk relative to Kasalath;1.2 Genetic analysis showed that the dwarf stature is controlled by recessive gene sdk,located in an approximate 2,600 Kb in the centromeric region of chromosome 2;1.3 When treated with GA3,the length of the second leaf sheaths of 'Kasalath' and sdk both elongated,indicating that the sdk mutant,like 'Kasalath',was sensitive to GA.2 By screening rice T-DNA insertion lines,we isolated a rice grain size mutant,larger grain size 1(lgsl).Grain length phenotype was clarified by genetic and histological experiments.The main results showed below:2.1 We characterized a grain size mutant Igsl(larger grain size 1)derived from rice activation-tagged T-DNA insertion lines.The increased cell number in the longitudinal direction of spikelet hulls was responsible for the grain length phenotype in lgsl.Quantitative real-time PCR(qRT-PCR)analyses showed that the relative expression levels of genes associated with cell cycle were higher in Igsl than WT,that may be the reason for increased cell number in spikelet hulls.2.2 Transgenic experiments confirmed that the mutant phenotype was caused by enhanced expression of OsbHLH107,mainly relied on the region 331-843 nt of the OsbHLH107 full length CDS,which was also the region for transcriptional activation.2.3 OsbHLH107 is a member of the basic helix-loop-helix(bHLH)transcription factors family,which is nuclear-localized and can form homodimer.2.4 Phylogenetic tree analysis showed that OsbHLH 107 belonged to the same phylogenetic tree subfamilies with OsPILs.OsPIL13(OsPIL1)and OsPIL16(APG)have been reported to regulate grain length in rice.By transgenic experiments,we found that OsPIL11 also exhibited its ability in grain length regulation.Taken together,we conclude that OsbHLH 107 and its homologs are important regulators in grain size development,which may be useful for grain yield improvement in rice breeding.