Fine Mapping and Candidate Gene Analysis For A Novel Male-Sterile Mutant Ms40 in Maize

Abstract Maize male sterile mutant 40 (ms40) was obtained from the progeny of ethyl methanesulfonate (EMS) treated inbred line RP125. Genetic analysis showed that it was controlled by a single recessive nuclear gene. Cytological observation of anthers revealed that abnormal cuticles and disappearing of Ubisch bodies presented in ms40. Moreover, its tapetum exhibited delayed degradation and blocked the formation of abnormal microspore. Using map-based cloning, ms40 locus was located in a 282-kb interval on chromosome 4, five annotated genes were predicted within this region. PCR-based sequencing detected a single nonsynonymous SNP (G>A) which changed glycine (G) to arginine (A) in the seventh exon of Zm00001d053895, while no difference was found for the other four genes between ms40 and RP125. Zm00001d053895 encodes the bHLH transcription factor bHLH51 which protein was located at nuclear. Phylogenetic analysis presented that bHLH51 had the highest homology with Sb04g001650, a tapetum degeneration retardation (TDR) bHLH transcription factor in Sorghum bicolor. Co-expression analysis exposed a total of 1192 genes coexpressed with Zm00001d053895 in maize, 647 out of 1192 were anther-specific genes. In summary, these findings are conducive to the marker-assisted selection of ms40 in hybrid breeding and laid a foundation for further studies on the mechanisms of male fertility.