Mazie Abigail R, Baum David A
Department of Botany, University of Wisconsin-Madison, 132 Birge Hall, 430 Lincoln Drive, Madison, WI 53706, United States.
Mol Phylogenet Evol. 2016 Jul;100:31-40. doi: 10.1016/j.ympev.2016.03.027. Epub 2016 Mar 22.
Positive selection is known to drive the evolution of genes involved in evolutionary arms races, but what role does it play in the evolution of genes involved in developmental processes? We used the single-celled epidermal trichomes of Brassicaceae as a model to uncover the molecular evolutionary processes that contributed to the transition from dendritic trichomes, as seen in most species of Brassicaceae, to the distinctive stellate trichomes of the genus Physaria. We explored the role of positive selection on the evolution of BRANCHLESS TRICHOME (BLT), a candidate gene for changes in trichome branching pattern. Maximum likelihood models of codon evolution point to a shift in selective pressure affecting the evolution of BLT across the entire Physaria clade, and we found strong evidence that positive selection has acted on a subset of Physaria BLT codons. Almost all of the 10 codon sites with the highest probability of having evolved under positive selection are clustered in a predicted coiled-coil domain, pointing to changes in protein-protein interactions. Thus, our findings suggest that selection acted on BLT to modify its interactions with other proteins. The fact that positive selection occurred throughout the radiation of Physaria could reflect selection to stabilize development in response to an abrupt switch from the dendritic form to the stellate form, divergent selection for diversification of the stellate form, or both. These results point to the need for evolutionary developmental studies of BLT and its interacting proteins in Physaria.
已知正向选择推动了参与进化军备竞赛的基因的进化，但它在参与发育过程的基因进化中起什么作用呢？我们以十字花科的单细胞表皮毛状体为模型，来揭示导致从十字花科大多数物种中所见的树状毛状体向 Physaria 属独特的星状毛状体转变的分子进化过程。我们探究了正向选择对 BRANCHLESS TRICHOME（BLT）进化的作用，BLT 是一个与毛状体分支模式变化相关的候选基因。密码子进化的最大似然模型表明，影响整个 Physaria 进化枝中 BLT 进化的选择压力发生了转变，并且我们发现有力证据表明正向选择作用于 Physaria BLT 密码子的一个子集。几乎所有在正向选择下进化概率最高的 10 个密码子位点都聚集在一个预测的卷曲螺旋结构域中，这表明蛋白质 - 蛋白质相互作用发生了变化。因此，我们的研究结果表明选择作用于 BLT 以改变其与其他蛋白质的相互作用。正向选择在 Physaria 的整个辐射过程中发生这一事实，可能反映了为响应从树状形态到星状形态的突然转变而进行的稳定发育选择、对星状形态多样化的分歧选择，或者两者兼而有之。这些结果表明需要对 Physaria 中的 BLT 及其相互作用蛋白进行进化发育研究。
