如何克服籼稻和粳稻杂种育性下降、结实率很低问题,是水稻育种家们几十年来苦苦求索的。中国科学院院士、华中农业大学教授张启发领衔的研究团队最近在这一领域取得重大进展,发现并成功分离克隆一个控制水稻籼粳杂种育性和广亲和性状的主效基因,命名为S5。该研究成果在水稻品种改良中具有重大应用前景。
研究人员称,驴马杂交产下子代(骡),而子代不具有正常生育能力。这种生殖隔离现象在植物中同样存在,如水稻籼粳亚种间杂种的不育性。但科学家们还发现,在水稻中存在一类特殊的种质资源称为广亲和品种,或偏于籼稻,或偏于粳稻,它们与籼稻和粳稻杂交的后代都表现正常可育。
张启发院士介绍说,栽培稻的籼粳不育和广亲和性的并存,在生物进化中是一种很奇特的现象:籼粳分化造就了丰富多样的稻种资源,也导致生殖隔离,而广亲和基因的存在则给籼粳亚种间基因交流提供桥梁,与籼稻或粳稻杂交都不影响杂种育性,对稻种的整体性有保障作用。他表示,有效地应用广亲和基因能够克服水稻籼粳亚种间杂种的不育性,从而利用籼粳亚种间强大的杂种优势提高水稻的产量。
广亲和基因因其重大的应用价值,在国内外水稻界被认为是一个非常重要的基因,早在我国启动863计划时,就列入了该基因分离克隆的研究内容。
张启发课题组从1990年就开始了该基因的研究,从遗传分析、基因定位到最终克隆出S5基因,历时18年,共有7家研究机构的20多位研究人员参与项目研究。该基因的成功克隆是我国科学家团结合作的结晶,8月12日的《美国科学院院刊》以封面文章形式发表了该研究团队的研究论文。(生物谷Bioon.com)
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PNAS August 12, 2008 vol. 105 no. 32 doi: 10.1073/pnas.0804761105
A triallelic system of S5 is a major regulator of the reproductive barrier and compatibility of indica–japonica hybrids in rice
Jiongjiong Chen*,, Jihua Ding*,, Yidan Ouyang*,, Hongyi Du*, Jiangyi Yang*, Ke Cheng*, Jie Zhao, Shuqing Qiu*, Xuelian Zhang?, Jialing Yao*, Kede Liu*, Lei Wang*, Caiguo Xu*, Xianghua Li*, Yongbiao Xue§, Mian Xia, Qing Ji‖, Jufei Lu‖, Mingliang Xu**, and Qifa Zhang*,
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.