Phenotypic characterization and genetic mapping of a new gene required for male and female gametophyte development in rice

Gametophyte development is an important process in flowering plants. Seeds are the primary organs for harvesting, and therefore spikelet fertility is especially vital for rice yield. Here, we report the characterization and genetic mapping of a novel rice male and female sterile mutant, mfs1, which was generated from a transgenic line of japonica rice variety Zhonghua 9. Anther transverse sections indicate that the microspores in these plants were abnormally degenerated at the meiotic leptotene stage, while the tapetum layer was not degenerated and remained present; therefore, no functional pollen grains formed in the mutant anther locules. In addition, the majority of mutant embryo sacs did not undergo differentiation or the differentiation was incomplete, resulting in the absence of functional embryo sac formation. Genetic analysis of three F2 populations indicated that the mutant phenotype was controlled by a single recessive gene. The mutant phenotype was confirmed by linkage analysis to be not due to a foreign T-DNA insertion. A map-based cloning strategy was employed to map the mutant gene, and, finally, the mfs1 locus was mapped to a 99-kb physical interval between simple sequence repeat markers RM12585 and D051 on rice chromosome 2. Sequence analysis indicates that 11 rice candidate genes are located in this region, including three encoded putative proteins and eight encoded known proteins, such as transcription factors having WRKY and zinc finger domains, a ubiquitin fusion degradation protein, chaperone protein clpB 1, a two-component response regulator, the ZOS2-04-C2H2 zinc finger protein, a peptidase of the T1 family and a protein kinase.