Cloning and Functional Study of A Rice Temperature Sensitive Female Sterility Gene

Male sterility line plays a fundamental role in hybrid rice breeding, whereas female sterility line seems useless due to the difficulty in maintaining a homozygote line. We have identified a rice germplasm showing female sterility from progenies of a crossing between japonica and indica varieties. After several generations of crossing and field observation, we found that the female sterility is thermo-sensitive, i.e. completely female-sterile under normal condition but partially recovered if irrigated with ‘cool’ water. Genetic analysis shows that it is controlled by a single recessive nuclear gene that we named as temperature-sensitive female sterility 1 (TFS1). Pollen viability testing indicates no difference between tfs1 and wild-type (WT) plants on pollen morphology and activity. Cytological studies have revealed that the development of embryo sac and pollen tube germination in tfs1 are normal compared with WT. However, egg cell was still observed after pollination for 3 days, indicating the double fertilization is blocked in tfs1 mutant. In addition, our fine mapping has located the mutation position to an 800kb DNA region.

In this proposed study, the cytological mechanism of double fertilization in tfs1 will be investigated. At the same time SNP and Indel markers inside this region will be developed for the fine mapping using a F2 population with more than 10 000 individuals of tfs1-nipponbare cross. Besides, deep-sequencing based Super BSA technology will also be used to accelerate the cloning of TFS1 gene. Finally, complementary experiments and other molecular and reverse genetic approaches (including RNA-seq, gel-free MS proteomics, transgenic method, mutant method and so on) will be used to study the possible mechanism of TFS1 in controlling double fertilization.

Producing hybrid rice seeds is still a labor-costing technology in agriculture. Female sterility, if it can be introduced into a restorer line as a pure pollen donor, has a great potential in reducing the cost, because the male and female parents of hybrid rice can be grown and harvested together by machines without worrying of seed purity. Thus, the outcome of this research shall not only help us better understand the genetic control of rice reproductive processes, but also provides the theoretical basis for reducing the labor cost in hybrid rice seed production.