Histological and transcriptional characterization of a novel recessive genic male sterility mutant in sesame (Sesamum indicum L.)

Recessive genic male sterility (RGMS) is an important approach to utilize heterosis, but the molecular mechanism of RGMS is not well understood in Sesamum indicum L. 95ms-5AB is a novel male sterility two-type line, which is controlled by a single RGMS gene. Histological observations revealed that abnormal inhibited male gametogenesis appeared during the mononuclear microspore stage. It was characterized by collapsed microspores, expanded vacuoles and the delayed degeneration of tapetum at the pollen maturation stage. To elucidate the mechanism of this RGMS, the transcriptional profiles of the sterile flower buds in 95ms-5A and the fertile flower buds in 95ms-5B were investigated using the cDNA-AFLP (amplified fragment length polymorphism) technique. About 30 reproducible differentially expressed transcript-derived fragments (TDFs) were detected, including 27 up-regulated from fertile buds and three from sterile buds. The functional analysis of 27 successfully cloned TDFs indicated that the corresponding genes of 11 TDFs may participate in the processes of energy metabolism, signal transduction and plant cell development. The other 16 TDFs were homologous to the proteins with unknown functions or with no homology in GenBank. Real-time PCR analysis of 21 genes in fertile and sterile buds at four different stages was used to validate and further investigate their expression patterns identified by cDNA-AFLP. Our results suggested that several genes related to callose wall or tapetum degeneration were suppressed in 95ms-5A even before the microspore mother cell stage, which led to delayed tapetum degeneration and blocked male gametogenesis. Several RGMS-related novel genes, including one stamen specially expressed gene, had also been identified that showed significantly different expression level between fertile and sterile buds along sesame male gametogenesis.