Neutral evolution of the nonbinding region of the anthocyanin regulatory gene Ipmyb1 in Ipomoea
Neutral evolution of the nonbinding region of the anthocyanin regulatory gene Ipmyb1 in Ipomoea
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DOI：
10.1534/genetics.104.034975
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发表时间：
2005-08-01
期刊：
影响因子：
3.3
通讯作者：
Rausher, MD
中科院分区：
文献类型：
--
作者：
Chang, SM;Lu, YQ;Rausher, MD
植物转录因子通常含有进化非常迅速的结构域。尽管有人提出，这种快速进化可能对物种之间的表型分化有很大贡献，但这一观点很少被明确测试。我们通过检测R2R3-MYB转录因子的快速进化的非DNA结合区来检验这一假设的有效性，该转录因子调节通心菜属花中花青素的表达。我们首先提供了证据表明，决定花是白色还是有色的紫花菜的WLocus对应于美国东南部种群中分离的MYB基因，一个功能等位基因和一个非功能等位基因。当结合区域表现出很大的选择性限制时，非结合区以平均K-a/K-S的速度进化。这一比率为0.74。这种进化速度的提高是由于放松了限制，而不是因为积极选择水平的提高。然而，尽管有这种放松的限制，类似于20-25%的密码子，随机分布在非结合区，受到高度限制，其余的中性进化，表明整个区域发挥着重要的功能(S)。我们的结果几乎没有迹象表明，这种调控基因的快速进化是由自然选择驱动的，或者它是通菜属物种之间花色差异的原因。
Plant transcription factors often contain domains that evolve very rapidly. Although it has been suggested that this rapid evolution may contribute substantially to phenotypic differentiation among species, this suggestion has seldom been tested explicitly. We tested the validity of this hypothesis by examining the rapidly evolving non-DNA-binding region of an R2R3-myb transcription factor that regulates anthocyanin expression in flowers of the genus Ipomoca. We first provide evidence that the Wlocus in Ipomoea purpurea, which determines whether flowers will be pigmented or white, corresponds to a myb gene segregating in southeastern U.S. populations for one functional allele and one nonfunctional allele. While the binding domain exhibits substantial selective constraint, the nonbinding region evolves at an average K-a/K-s. ratio of 0.74. This elevated rate of evolution is due to relaxed constraint rather than to increased levels of positive selection. Despite this relaxed constraint, however, similar to 20-25% of the coclons, randomly distributed throughout the nonbinding region, are highly constrained, with the remainder evolving neutrally, indicating that the entire region performs important function(s). Our results provide little indication that rapid evolution in this regulatory gene is driven by natural selection or that it is responsible for floral-color differences among Ipomoea species.