长久以来，杂交育种被用于改善农作物，但是当两种亚洲主要水稻品种杂交时，经常产生一种更强壮但是不育的杂交品种。张启发及其同事发现了一种此前未知的基因——他们将其命名为S5——造成了籼稻和粳稻这两种主要水稻品系的杂交品种不育。两种稍有不同的S5基因——籼稻和粳稻各有一种——导致水稻健康而可育，但是当来自这两种水稻的这种基因通过杂交培育结合到一起之后，它们的后代是高度不育的。相关论文发表在美国《国家科学院院刊》（PNAS）上。
这组科学家还研究了另一种具有“广亲和性”的水稻品系，结果发现它的S5基因的一大段序列丢失是广亲和性水稻与其他两种水稻杂交时能产生可育品种的原因。他们对另外16种亚洲水稻品种进行了取样，证实了S5基因的角色，首次为大多数籼-粳杂交稻为何不育提供了直接的原因证据。这组作者提出，他们的结果可以帮助改善水稻培育，并为全世界提供更优良的水稻作物。（生物谷Bioon.com）
生物谷推荐原始出处：
PNAS，doi: 10.1073/pnas.0804761105，Jiongjiong Chen，Qifa Zhang
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.
