Yang Yu, Zhigang Zhao, Yanrong Shi, Hua Tian, Linglong Liu, Xiaofeng Bian, Yang Xu, Xiaoming Zheng, Lu Gan, Yumin Shen, Chaolong Wang, Xiaowen Yu, Chunming Wang, Xin Zhang, Xiuping Guo, Jiulin Wang, Hiroshi Ikehashi, Ling Jiang, and Jianmin Wan

Genetics July 2016 203:1439-1451

Abstract

Intersubspecific hybrid sterility is a common form of reproductive isolation in rice (Oryza sativa L.), which significantly hampers the utilization of heterosis between indica and japonica varieties. Here, we elucidated the mechanism of S7, which specially causes Aus-japonica/indica hybrid female sterility, through cytological and genetic analysis, map-based cloning, and transformation experiments. Abnormal positioning of polar nuclei and smaller embryo sac were observed in F₁ compared with male and female parents. Female gametes carrying S7^cp and S7ⁱ were aborted in S7^ai/S7^cp and S7^ai/S7ⁱ, respectively, whereas they were normal in both N22 and Dular possessing a neutral allele, S7ⁿ. S7 was fine mapped to a 139-kb region in the centromere region on chromosome 7, where the recombination was remarkably suppressed due to aggregation of retrotransposons. Among 16 putative open reading frames (ORFs) localized in the mapping region, ORF3 encoding a tetratricopeptide repeat domain containing protein was highly expressed in the pistil. Transformation experiments demonstrated that ORF3 is the candidate gene: downregulated expression of ORF3 restored spikelet fertility and eliminated absolutely preferential transmission of S7^ai in heterozygote S7^ai/S7^cp; sterility occurred in the transformants Cpslo17-S7^ai. Our results may provide implications for overcoming hybrid embryo sac sterility in intersubspecific hybrid rice and utilization of hybrid heterosis for cultivated rice improvement.

See: http://www.genetics.org/content/203/3/1439?etoc