裸子植物中光敏色素PHY-PAS1 结构域的适应性进化

光敏色素是一类红光/远红光受体, 在植物种子萌发到成熟的整个生长发育过程中均起重要的调节作用。光敏色素PHYPAS1 结构域存在于光敏色素基因家族的所有成员中, 对调节发色团的光谱特性和光信号转导非常关键。光敏色素基因家族通过基因重复产生, 而基因重复可能与物种形成有关。PHYP基因是裸子植物光敏色素基因家族发生第1次重复后产生的, 并且以单拷贝形式存在。为了研究不同裸子植物PHYP基因编码蛋白的PHY-PAS1结构域在进化过程中是否受到相同的选择压力以及是否发生了适应性进化, 该研究利用分支模型、位点模型以及分支-位点模型对裸子植物31条PHYP基因序列编码蛋白的PHY-PAS1结构域所受到的选择压力进行了分析。结果表明, 在由PHY-PAS1结构域序列构建的系统树中, 多数分支处于强烈的负选择压力下 (w<1); 有14个分支处于正选择压力下 (w>1), 其中13个分支发生在属内种间; 与之相比, 在较为古老的谱系中相对缺少这种正选择压力。

Adaptive Evolution in the PHY-PAS1 Domain of PHYP in Gymnosperms

Phytochromes, which receive and transmit signals generated by red and far- red light, can regulate a wide range of developmental and physiological responses during plant development. Their PHY-PAS1 domain is critical for tuning spectroscopic properties of the bound bilin and signal transduction and exists in all members of the gymnosperm phytochrome gene family created by gene duplication. Gene duplications can play significant roles in speciation. The PHYP gene occurs from the first gene duplication event, as a single copy. To further test whether PHY-PAS1 domains in PHYP have experienced the same constraint or positive selection during their evolution in distinct gymnosperm species , we assayed the molecular evolution of 31 gymnosperm PHY-PAS1 domain sequences under the branch, site and branch-site models. Most lineages are highly conserved, with w< 1, but 14 lineages evolved under positive selection, with w> 1; among them 13 lineages are of co-generic species. By contrast, such selective pressure is not detected in more distantly related species.