Viaene Tom, Vekemans Dries, Irish Vivian F, Geeraerts Anke, Huysmans Suzy, Janssens Steven, Smets Erik, Geuten Koen
Laboratory of Plant Systematics, Institute of Botany and Microbiology, P.O. Box 2437, Leuven, Belgium.
Mol Biol Evol. 2009 Nov;26(11):2627-45. doi: 10.1093/molbev/msp181. Epub 2009 Aug 13.
Basal asterid families, and to a lesser extent the asterids as a whole, are characterized by a high variation in petal and stamen morphology. Moreover, the stamen number, the adnation of stamens to petals, and the degree of sympetaly vary considerably among basal asterid taxa. The B group genes, members of the APETALA3 (AP3) and PISTILLATA (PI) gene lineages, have been shown to specify petal and stamen identities in several core eudicot species. Duplicate genes in these lineages have been shown in some cases to have diversified in their function; for instance in Petunia, a PI paralog is required for the fusion of stamens to the corolla tube, illustrating that such genes belonging to this lineage are not just involved in specifying the identity of the stamens and petals but can also specify novel floral morphologies. This motivated us to study the duplication history of class B genes throughout asterid lineages, which comprise approximately one-third of all flowering plants. The evolutionary history of the PI gene subfamily indicates that the two genes in Petunia result from an ancient duplication event, coinciding with the origin of core asterids. A second duplication event occurred before the speciation of basal asterid Ericales families. These and other duplications in the PI lineage are not correlated with duplications in the AP3 lineage. To understand the molecular evolution of the Ericales PI genes after duplication, we have described their expression patterns using reverse transcription polymerase chain reaction and in situ hybridization, reconstructed how selection shaped their protein sequences and tested their protein interaction specificity with other class B proteins. We find that after duplication, PI paralogs have acquired multiple different expression patterns and negative selective pressure on their codons is relaxed, whereas substitutions in sites putatively involved in protein-protein interactions show positive selection, allowing for a change in the interaction behavior of the PI paralogs after duplication. Together, these observations suggest that the asterids have preferentially recruited PI duplicate genes to diverse and potentially novel roles in asterid flower development.
基部菊类植物科，以及在较小程度上整个菊类植物，其特征是花瓣和雄蕊形态变化很大。此外，基部菊类植物类群的雄蕊数量、雄蕊与花瓣的合生情况以及花瓣联合程度差异很大。B组基因是APETALA3（AP3）和PISTILLATA（PI）基因谱系的成员，已被证明在几个核心真双子叶植物物种中决定花瓣和雄蕊的特征。这些谱系中的重复基因在某些情况下已显示出功能多样化；例如在矮牵牛中，一个PI旁系同源基因是雄蕊与花冠管融合所必需的，这表明属于该谱系的此类基因不仅参与决定雄蕊和花瓣的特征，还可以决定新的花形态。这促使我们研究整个菊类植物谱系中B类基因的重复历史，菊类植物约占所有开花植物的三分之一。PI基因亚家族的进化历史表明，矮牵牛中的两个基因源于一次古老的重复事件，与核心菊类植物的起源相符。第二次重复事件发生在基部菊类植物杜鹃花目科物种形成之前。PI谱系中的这些以及其他重复事件与AP3谱系中的重复事件不相关。为了了解杜鹃花目PI基因重复后的分子进化，我们使用逆转录聚合酶链反应和原位杂交描述了它们的表达模式，重建了选择如何塑造它们的蛋白质序列，并测试了它们与其他B类蛋白质的蛋白质相互作用特异性。我们发现，重复后，PI旁系同源基因获得了多种不同的表达模式，其密码子上的负选择压力有所放松，而假定参与蛋白质-蛋白质相互作用的位点上的替换显示出正选择，这使得PI旁系同源基因在重复后相互作用行为发生改变。总之，这些观察结果表明，菊类植物优先将PI重复基因招募到菊类植物花发育中不同且可能新的角色中。
