Characterization And Gene Mapping Of A Recessive Male Sterile Mutant Osnp3 In Rice

Male sterility plays a significant role in the utilization of rice heterosis.In this study,a no-pollen male sterile mutant osnp3 was identified in the tissue culture progeny of Zhonghua 11（a japonica rice）.In order to understand the molecular mechanism of the male sterility in osnp3,the characterization,gene mapping,and candidate screening were performed.This study provided the germplasm resources and theoretical basis for the applications of recessive male genic male sterility and related genes in hybrid rice breeding.1.Mutation of osnp3 had significant effects on pollen fertility and not onagronomic traitsBased on the comparative analysis of the agronomic traits,spikelet,flower organs,and pollen grains between Zhonghua 11 and osnp3 mutant,we found no obvious differents on agronomy traits,spikelet shape and flower organ structure.However,the anthers of osnp3 were thin and white,and had no pollens released during flowering,which resulted in complete sterility.The results indicate that the mutated genes have significant effects on anther morphology and pollen development.The results of semi-thin section showed that the anther tapetum cells of osnp3 were degraded abnormally,the microspore cells could not accumulate starch for pollen filling,the microspore cells degenerated,and finally the mature pollen grains could not be developed,which caused complete abortion.2.The sterility of osnp3 is controlled by a recessive nuclear geneThe F₁of osnp3╳wild Zhonghua 11 was fertile,and the progenies of a heterozygous plant showed a 3:1 ratio of normal plant to sterile plant,which indicates that the male sterility in mutant is controlled by a recessive nuclear gene.3.OsNP3 gene locates on the rice chromosome 4Preliminary location:The osnp3 gene was mapped in an interval of 3.1Mb on the long arm of chromosome 4 between markers 0424 and 04010.Fine mapping:The target gene was further fine mapped between markers C04D1and C04D3（a physical distance of 0.96 Mb）,and OsNP3 gene was co-segregated with markers 04008 and C04D2.4.The candidate gene for OsNP3 is LOC＿Os04g51070By genome re-sequencing,approximately 4 kb of retrotransposon insertion was found on the third exon of Loc＿Os04g51070,and no mutation was found in other loci,which indicated that Loc＿Os04g51070 was the candidate.ThericegenomeAnnotationProjectDatabase（http//rice.plantbiology.msu.edu/index.shtml）indicates the candidate encodes a b HLH transcription factor that may be involved in the degradation of rice anther tapetum cells through transcriptional regulation.The insertion of the retrotransposon may result in the loss of the function of the gene,which leads to the failure of PCD in tapetum cells and the abortion of pollen.