Phenotype Identification And Gene Mapping Of Paa934 And Paa1331 In Rice

Rice panicle apical abortion(PAA)is one of the main factors restricting the rice yield.In recent years,there have been many studies on PAA mutants,some QTL locus and genes have been revealed,but the current regulatory network on PAA has not yet formed,remains need lots of research.In this study,two panicle apical abortion mutants(paa934and paa1331)were identified from an ethyl methyl sulfate(EMS)mutagenized population of Yixiang 1B.The investigation of agronomic traits,histological observation,genetic analysis,and gene mapping cloning were performed.The main results are as follows:1.paa934:The phenotypic observation showed that the panicle apical abortion led to paa934 was shorter than wild type.In addition,the main panicle length,tiller number,grain number per panicle and grain weight were lower than that of wild type,the degradation rate was higher than wild type and was close to 50%.Besides,We noticed there were red brown lesion spots appeared on the tip of mutant leaves after sowing two weeks,remained until mature stage,and disappeared.Transverse section observation found that the spikelet degeneration was accompanied with programmed cell death(PCD),and the vascular bundle of branch showed defects of development.Genetic analysis showed that mutant phenotype is a recessive trait controlled by a single gene.Map-based cloning found an annotated gene LOC＿Os04g56160,located on the long arm o f chromosome 4,its thirteenth exon showed that a G-to-A single base substitution,which resulted in a premature stop codon.This gene encodes OSA7 protein,which is a plasma membrane H~+-ATPase.OSA7 is composed of about 951 amino acid residues,containing four structural domains.Gene mutation led to the loss of active catalytic structure of OSA7 and inhibit its activity.Above al,we consider Os OSA7 as mutation candidate gene.2.paa1331:Compared the mutant phenotype with wild type,we found that the mutant was lower in plant height,tiller number,main panicle length and seed setting rate,the degradation rate was as high as 53%.Due to the apical abortion,the mutant plant height became shorter.Transverse section observation was carried out,the degradation floret showed stamens shrivel and distorted glume,besides,the spikelet degeneration of mutants was accompanied with programmed cell death.The growth dynamics of the degraded spikelet showed that the young spike began to degenerate during the meiosis of pollen development,resulting in no pollen formation.The content of C TK in mutants was lower than that of wild type,while IAA was higher than wild type.Genetic analysis showed that mutant trait was controlled by a recessive gene.Combined analysis of initial location and De novo genome sequencing,one gene on chromosome 4 was found,LOC＿Os04g40720,the fourth exon of it showed that a A-to-G single base substitution,which resulted in a change from Asn to Asp.The gene encoding expression protein was predicted to be composed of 1394 amino acid residues.We consider LOC＿Os04g40720 as candidate gene of paa1331.