裸子植物psbA基因分子进化式样的研究

Molecular Evolutionary Patterns of the psbA Gene in Gymnosperms

摘要:

为阐明裸子植物对陆生生境生态响应的分子机制,以新近的裸子植物分类系统为指导,基于psbA基因编码全序列对4亚纲53种代表植物进行分子进化分析。首先,依据"放松分子钟"模型重建裸子植物在时间尺度下系统发育关系;其次,采用6个模型(MEC/JTT、MEC/cpREV、M5、M7、M8、M8a)估测氨基酸位点ω值,并对各模型结果进行统计检测;随后,利用Bootstrap方法检PSBA蛋白内部氨基酸位点的共进化动态。结果表明,系统树提示的物种分化历程支持前期分类结果; 光合系统反应中心核心PSBA蛋白有3个氨基酸位点(13、19和243)曾经受正选择压力;PSBA蛋白内部有多对氨基酸位点间构成了共进化网络。因此,psbA基因编码序列具有作为描绘裸子植物系统发育关系标记的潜力,PSBA蛋白部分位点经历了适应性进化,通过位点间共进化网络协同作用方式辅助裸子植物响应陆生生境。

Abstract:

To understand the molecular mechanisms of ecological responding to terrestrial habitat in gymnosperm species, 53 representative species, belonging to four subclasses of gymnosperms, were selected to molecular evolutionary analysis based on psbA gene coding sequences. Firstly, the phylogenetic tree under geological timescale was established based on relaxed molecular clock model. Secondly, the positive selection signal among PSBA were detected by the estimated ω values by using six models, including MEC/JTT, MEC/cpREV, M5, M7, M8 and M8a. Then, the co-evolutionary network of amino acid sites within the PSBA was investigated by Bootstrap method. The results indicated that the species differentiation process from phylogenetic tree of gymnosperms along the timescale supported to previous studies. The three amino acid sites (13, 19, 243) in PSBA protein endured positive selection during the evolutionary history of gymnosperm species. Certain pairs of site within PSBA protein evolved into a co-evolutionary network. Therefore, the psbA sequences have the potential to be DNA marker during the establishment of the phylogenetic relationship of gymnosperms. The modification of PSBA protein by the site adaptation and protein intra network might be an important factor benefits the adaptive evolution of gymnosperm species against the terrestrial habitat.