title: A triallelic system of S5 is a major regulator of the reproductive barrier and compatibility of indica-japonica hybrids in rice.
abstract: 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.
authors.affiliation: National Key Laboratory of Crop Genetic Improvement and National Centre of Plant Gene Research, Huazhong Agricultural University, Wuhan 430070, China.
authors.forename: Jiongjiong
authors.initials: J
authors.lastname: Chen
authors.forename: Jihua
authors.initials: J
authors.lastname: Ding
authors.forename: Yidan
authors.initials: Y
authors.lastname: Ouyang
authors.forename: Hongyi
authors.initials: H
authors.lastname: Du
authors.forename: Jiangyi
authors.initials: J
authors.lastname: Yang
authors.forename: Ke
authors.initials: K
authors.lastname: Cheng
authors.forename: Jie
authors.initials: J
authors.lastname: Zhao
authors.forename: Shuqing
authors.initials: S
authors.lastname: Qiu
authors.forename: Xuelian
authors.initials: X
authors.lastname: Zhang
authors.forename: Jialing
authors.initials: J
authors.lastname: Yao
authors.forename: Kede
authors.initials: K
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Caiguo
authors.initials: C
authors.lastname: Xu
authors.forename: Xianghua
authors.initials: X
authors.lastname: Li
authors.forename: Yongbiao
authors.initials: Y
authors.lastname: Xue
authors.forename: Mian
authors.initials: M
authors.lastname: Xia
authors.forename: Qing
authors.initials: Q
authors.lastname: Ji
authors.forename: Jufei
authors.initials: J
authors.lastname: Lu
authors.forename: Mingliang
authors.initials: M
authors.lastname: Xu
authors.forename: Qifa
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000483:Alleles; D001483:Base Sequence; D001947:Breeding; D002678:Chimera / Q000235:genetics*; D003001:Cloning, Molecular; D051456:Gene Flow; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics*; D051479:Plant Infertility / Q000235:genetics*; D040641:Quantitative Trait Loci / Q000235:genetics*; D013045:Species Specificity