Department of Genetics and Biochemistry, Clemson University, Clemson, SC 29631, USA.
Mol Ecol. 2010 Aug;19(16):3243-5. doi: 10.1111/j.1365-294X.2010.04709.x.
Examining the targets of selection in crop species and their wild and weedy relatives sheds light on the evolutionary processes underlying differentiation of cultivars from progenitor lineages. On one hand, human-mediated directional selection in crops favours traits associated with the streamlining of controllable and predictable monoculture practices alongside selection for desired trait values. On the other hand, natural selection in wild and especially weedy relatives presumably favours trait values that increase the probability of escaping eradication. Gene flow between crops and wild species may also counter human-mediated selection, promoting the evolution and persistence of weedy forms. In this issue, two studies from a group of collaborators examine diversity and divergence patterns of genes underlying two traits associated with red rice (Oryza sp.), the conspecific relative of cultivated rice (Oryza sativa) that is a non-native weed (see Fig. 1). In the first study by Gross et al. (2010), genetic variation in the major gene underlying the hallmark red pigmentation characterizing most weedy rice (Rc) is found to have a pattern consistent with non-reversion from U.S. cultivated rice (i.e. the cultivar did not 'go feral'). This suggests that U.S. weedy rice is not an escaped lineage derived from U.S. cultivated rice populations; weedy rice likely differentiated prior to the selective sweep occurred in this gene within cultivated rice populations. Using the major seed shattering locus sh4 gene and the neighbouring genomic region, Thurber et al. (2010) track the molecular evolutionary history of the high shattering phenotype, a trait contributing dramatically to the success of crop selection in cultivated rice as well as the persistence and expansion of weedy red rice. In this study, the shared fixation of a sh4 mutation in both cultivated rice and weedy rice indicates that weedy rice arose subsequent to the strong selective sweep leading to significant reduction in seed shattering in cultivated rice.
研究作物物种及其野生和杂草亲缘种的选择靶标，可以揭示栽培品种与其祖先谱系分化的进化过程。一方面，人类在作物中的有目的选择有利于与简化可控和可预测的单一种植实践相关的特征，同时也有利于选择所需的特征值。另一方面，野生和特别是杂草亲缘种中的自然选择可能有利于增加逃避根除的可能性的特征值。作物和野生种之间的基因流也可能对抗人类介导的选择，促进杂草形式的进化和持续存在。在本期杂志中，一组合作者的两项研究检查了与红稻（Oryza sp.）两个特征相关的基因的多样性和分化模式，红稻是栽培稻（Oryza sativa）的同种近缘种，是一种非本地杂草（见图 1）。在 Gross 等人的第一项研究中（2010 年），发现主导特征的主要基因中的遗传变异表明，具有特征性的标志性红色素的大多数杂草稻（Rc）不太可能从美国栽培稻中逆转（即该品种没有 '野性化'）。这表明美国杂草稻不是源自美国栽培稻种群的逃逸谱系；杂草稻可能在栽培稻种群中该基因发生选择性清除之前就已经分化了。Thurber 等人（2010 年）使用主要的种子崩解位点 sh4 基因和邻近的基因组区域，追踪高崩解表型的分子进化历史，这一特征对栽培稻的作物选择以及杂草红稻的持续存在和扩张有很大的贡献。在这项研究中，栽培稻和杂草稻中 sh4 突变的共同固定表明，杂草稻是在导致栽培稻种子崩解显著减少的强烈选择性清除之后出现的。
