triallelic system of S5 is a major regulator of the reproductive barrier and compatibility of indica-japonica hybrids in rice

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 105; no. 32; pp. 11436 - 11441
• Main Authors: Chen, Jiongjiong, Ding, Jihua, Ouyang, Yidan, Du, Hongyi, Yang, Jiangyi, Cheng, Ke, Zhao, Jie, Qiu, Shuqing, Zhang, Xuelian, Yao, Jialing, Liu, Kede, Wang, Lei, Xu, Caiguo, Li, Xianghua, Xue, Yongbiao, Xia, Mian, Ji, Qing, Lu, Jufei, Xu, Mingliang, Zhang, Qifa
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12-08-2008; National Acad Sciences
• Series: From the Cover
• Subjects: Alleles; amino acid sequences; aspartic proteinases; Base Sequence; Biological Sciences; Breeding; Cells; Chimera - genetics; Cloning; Cloning, Molecular; embryo sac; exons; gene expression; Gene Flow; Genes; Genetic loci; Hybridity; Hybridization; hybrids; loci; messenger RNA; Molecular Sequence Data; nucleotide sequences; Oryza - genetics; Oryza sativa; Plant fertility; Plant Infertility - genetics; Plant reproduction; Plants; Pollen; Polymerase chain reaction; Proteases; Proteins; Quantitative Trait Loci - genetics; Rice; S5 locus; Species Specificity; Spikelets; SS-I allele; SS-j allele; varieties
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0804761105

Hybrid sterility is a major form of postzygotic reproductive isolation. Although reproductive isolation has been a key issue in evolutionary biology for many decades in a wide range of organisms, only very recently a few genes for reproductive isolation were identified. The Asian cultivated rice (Oryza sativa L.) is divided into two subspecies, indica and japonica. Hybrids between indica and japonica varieties are usually highly sterile. A special group of rice germplasm, referred to as wide-compatibility varieties, is able to produce highly fertile hybrids when crossed to both indica and japonica. In this study, we cloned S5, a major locus for indica-japonica hybrid sterility and wide compatibility, using a map-based cloning approach. We show that S5 encodes an aspartic protease conditioning embryo-sac fertility. The indica (S5-i) and japonica (S5-j) alleles differ by two nucleotides. The wide compatibility gene (S5-n) has a large deletion in the N terminus of the predicted S5 protein, causing subcellular mislocalization of the protein, and thus is presumably nonfunctional. This triallelic system has a profound implication in the evolution and artificial breeding of cultivated rice. Genetic differentiation between indica and japonica would have been enforced because of the reproductive barrier caused by S5-i and S5-j, and species coherence would have been maintained by gene flow enabled by the wide compatibility gene.