Identification And Functional Analysis Of SD38 Gene For Plant Height In Rice(Oryza Sativa L.)

Plant height as an important rice agronomic trait,affects rice yields and lodging resistance.In this study,a semi-dwarf mutant named sd38 was screened from T-DNA insertion mutant progenies of cv.Hwayoung background and showed reduced height and small grains phenotype.Identification of T-DNA insertion,artificial transgenic validation and functional analysis revealed the causes and molecular mechanisms of mutant phenotype changes.Our research should be useful for application of dwarf mutants in breeding.The main results are as follows:1.Compared to WT,sd38 mutant showed reduced height,small grain and thin stem sclerenchyma.Histological analysis revealed reduced cell size in stem and inner surface of lemma was main cause of dwarf and small grain phenotype.Scanning electron microscope showed secondary wall of stem sclerenchyma in sd38 mutant was significantly thinner than that of WT.2.Genetic analysis showed that semi-dwarf trait was regulated by a single dominant gene SD38.A T-DNA fragment was found inserted to 5'-UTR region of OsWRKY36 gene by molecular identification,resulting in OsWRKY36 overexpressing in sd38 mutant.OsWRKY36 overexpressed transgetic plants showed semi-dwarfness,small grain with reduced cell size,which were similar to sd38.So we detemined that SD38 encoded OsWRKY36 protein.The height of OsWRKY36 RNAi transgetic plants had no difference with control but grain size was increased.Therefore we concluded that overexpression of SD38/OsWRKY36 repressed cell expansion thereby causing semi-dwarf and small grain phenotype.3.SD38/OsWRKY36 was expressed in most tissues,especially stems,leaves and leaf sheaths,and the protein was localized in the nucleus.Yeast transactivation activity assays indicated that OsWRKY36 had transactivation activity.N terminus of the protein is necessary for transactivation activity,while C terminus containing a WRKY domain repressed transactivation activity of the N terminus;WRKY domain can bind to special motifs in promoter of targets and regulates their expression.These results indicated OsWRKY36 functions as atranscription factor.4.Phloroglucinol staining and quantity of lignin and cellulose showed lignin content was significantly reduced in sd38 and overexpressed transgetic plants compared to their controls.qRT-PCR results revealed genes involved in secondary wall synthesis were significantly downregulated in sd38.SWN1 and SWN2,the positive regulators of secondary wall synthesis,were negatively regulated by OsWRKY36.The dual-luciferase system detection assay revealed OsWRKY36 can repressed transcription of SWN2 gene by binding to its promoter.So we concluded SD38/OsWRKY36 influenced lignin synthesis by negatively regulating SWN2.Stem lignin contributes to abiotic stress resistance in plants.Abiotic stress treatments showed sd38 was sensitive to abiotic stress,indicating SD38/OsWRKY36 involved in plant response to abiotic stress.