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The gamyb5,a no pollen male sterile mutant was identified from the mutant library of 60Co-γ-treated indica cultivar Zhonghui8015(Zh8015).There were not significantly differences in agronomic traits such as plant type,height and tiller number between gamyb5 mutant and wild-type.But gamyb5 showed slender filaments and white anthers with no muture pollen grains.gamyb5 as the pollen acceptor,was crossed with wild type Zh8015 and a japonica cultivar 02428,respectively.Genetic analysis of all hybridization populations indicated that gamyb5 was controlled by a single recessive nuclear gene which was mapped on the long arm of chromosome1.With developed SSR,Indel markers and F2 mapping population of gamyb5/02428,the gene was fine mapped to a region of 16-kb on the long arm of chromosome 1 between markers ZF-29 and ZF-31.Sequence analysis of the two ORFs in this region revealed that the LOC_Os01g0812000,which encodes a gibberellin-induced MYB transcription factor,had an 8 nucleotides bases deletion in the second extron probably responsible for the male sterility phenotype.Anther semi-thin results showed the microspore mother cells seemed to have abnormal meiosis and no obvious formation of functional tetrads and microspores in gamyb5 mutant.Moreover,tapetal cells of gamyb5 became abnormally enlarged and the tapetum PCD was delayed.Additionally,real-time fluorescent quantitative PCR analysis showed that the expression level of the important gene UDT1,CYP703A3 and CYP704B2 in anther decreased significantly in gamyb5,indicating these three genes likely located downstream of the GAMYB gene.