Speciation has long been regarded as an irreversible process once the reproductive barriers had been established. However, unlike in natural populations, artificial selection might either accelerate or prevent speciation processes in domesticated species. Asian cultivated rice is a target crop for both domestication and artificial breeding; it contains two subspecies of indica and japonica, which usually produce sterile inter-subspecific hybrids due to reproductive barriers. In this study, we constructed the evolutionary trajectory of a reproductive isolation system S5, which regulates fertility in indica–japonica hybrids via three adjacent genes, based on the data of 606 accessions including two cultivated and 11 wild rice species. Although hybrid sterility haplotypes at S5 lead to establishment of a killer-protector reproductive barrier, origin of wide-compatibility haplotypes by complex hybridization and recombination provides an opposing force to reproductive isolation and thus prevents speciation during domestication. Analysis in a diallel set of 209 crosses involving 21 parents showed that the wide-compatibility genotypes largely rescued fertility of indica–japonica hybrids, indicating that the wide-compatibility gene would enable gene flow to maintain species coherence. This counteracting system indicates that combined effects of natural evolution and artificial selection may result in reversible processes of speciation in rice, which may also have implications for genetic improvement of rice.

一旦建立了繁殖障碍，物种形成长期以来就被认为是不可逆转的过程。但是，与自然种群不同，人工选择可能会加速或阻止驯化物种的物种形成过程。亚洲栽培稻是驯化和人工育种的目标作物。它包含of稻和粳稻两个亚种，由于繁殖障碍，它们通常会产生不育的亚种间杂种。在这项研究中，我们构建了一个生殖隔离系统S5的进化轨迹，该系统调节in-粳稻的繁殖力基于606个种质的数据，包括两个栽培稻种和11种野生稻种，通过三个相邻基因杂交。尽管在S5处杂交的不育单倍型导致建立了杀手-保护子生殖屏障，但是通过复杂的杂交和重组产生的广泛相容性单倍型为生殖分离提供了相反的力量，从而防止了驯化期间的物种形成。对涉及21个亲本的209个杂交的二系分析表明，广泛兼容的基因型在很大程度上拯救了–粳的繁殖力。杂种，表明广泛兼容的基因将使基因流动，以保持物种的连贯性。该抵消系统表明，自然进化和人工选择的综合作用可能导致水稻形成过程的可逆过程，这也可能对水稻的遗传改良产生影响。