Key genes and molecular mechanisms responsible for male sterility revealed by transcriptome analysis in cotton

A novel male sterility line Nan A forms normal microspore tetrads, but defective pollen development. Dysregulated fertility/stress-related genes in anthers cause cotton male sterility. Cotton exhibits significant heterosis, characterization of genic male-sterility (GMS) genes is crucial for unraveling molecular mechanisms controlling anther and pollen development, and enables the development of biotechnology-based male-sterility systems for commercial hybrid seed production. Here, we report a combined cytological and transcription analyses of the anther of a single-gene recessive GMS line Nan A and its near-isogenic male fertile line Nan B, and further verified the functions of two male sterility-related genes. Nan A developed shorter stamen filaments, produced sterile pollens characterized by shriveled starch grains inside, delayed nexin deposition, without spines on exine surface, and failure in dehiscence. A number of anther-preferentially expressed genes were unexpectedly up-regulated in Nan A, whereas loss-of-function mutants of their homologous genes in other plant species exhibit male sterility. By contrast, a number of stress-related transcription activation protein genes are down-regulated in Nan A. Either silencing the anther specifically expressed GhCYP450 that down-regulated or overexpressing GhPHD-D that up-regulated in Nan A can convert wild-type into male sterility. Our results indicate that timely expression of anther and/or pollen developmental genes are pivotal for male fertility.