全基因组复制事件的绝对定年揭示莲座蕨属植物的迟滞演化

Dating whole-genome duplication reveals the evolutionary retardation of Angiopteris

全基因组复制在维管植物的物种形成过程中普遍存在,被认为是物种适应极端环境的重要机制之一。确定全基因组复制事件的发生时间对理解生物的适应性演化具有重要意义。然而,在维管植物,特别是蕨类植物中,全基因组复制事件的发生时间及其演化意义仍知之甚少。本研究以蕨类植物重要基部类群——福建莲座蕨(Angiopteris fokiensis)为例,基于不同采样点(广东、广西、上海)的3个转录组学数据,利用同义替换率(Ks)和绝对定年的方法分析全基因组复制事件的发生时间和物种单位时间内的分子演化速率,并对事件发生后保留下的基因进行基因功能注释和富集分析。结果表明,福建莲座蕨在159-165Mya发生了一次全基因组复制事件,该复制事件优先保留的基因主要与营养代谢、信号传导、适应调节和组织结构生长相关。另外,福建莲座蕨的分子演化速率为1.66×10^(-9)(同义替换/位点/年),是除裸子植物外,陆生植物中已知演化速率最缓慢的类群。综合以上研究结果,我们推测福建莲座蕨全基因组复制的发生可能与裸子植物繁盛、核心被子植物集中兴起或托阿尔阶灭绝事件有关。而复制后显著保留基因可能促进了莲座蕨属(Angiopteris)植物的遗传和形态创新,从而帮助其快速适应环境的剧烈变化。进一步对该类群植物演化速率缓慢的原因进行讨论,推测莲座蕨属缓慢的演化速率可能与其本身世代周期长、基因组较大及其生长环境稳定有关。本研究通过分析福建莲座蕨的全基因组复制历史和复制基因的保留模式,推测全基因组复制事件对促进演化速率较慢的植物适应极端环境变化具有重要意义,可为理解其他陆生植物的适应性演化提供更多启发。

Aim:Whole-genome duplication(WGD)plays a positive role in speciation in vascular plants and is considered to be an important mechanism for species adaptation to the extreme environments.Dating whole-genome duplication events in different species is essential for understanding the adaptive evolution of organisms.However,the role that these mechanisms play in vascular plants,especially ferns,is still poorly understood.Method:Based on the synonymous substitution rates(Ks)and absolute dating of the WGD event,this study used three different transcriptome sequences of Angiopteris fokiensis to analyze the contribution of polyploidy to the evolution of plants,and the silent substitution rate.Gene annotation and functional enrichment were carried out to elucidate the biological processes,molecular function,and cellular component for the genes retained after the WGD.Results:We found that there was at least one WGD event in A.fokiensis at 159–165 Mya,and most duplicated genes were often related to nutrient metabolism,signal transduction,adaptive regulation and anatomical structure development.The silent substitution rate of A.fokiensis is 1.66×10^(-9)synonymous substitutions per site per year.Based on the above results,we speculate that the WGD event was associated with gymnosperms flourishing and the emergence of core angiosperms,or the Toarcian extinction event.The retention of particular genes after the WGD may have promoted genetic and morphological innovation in Angiopteris,thus helping it adapt to the drastic changes in environmental conditions.At present,A.fokiensis is the slowest evolving group of land plants except gymnosperms,which may relate to the long generation time,large genome and stable living habitat.Conclusion:In this study,we analyzed the whole-genome duplication history and the patterns of retention of duplicated genes in A.fokiensis,suggesting that WGD events are of great influence in promoting the adaptation to extreme environmental changes of plants with slower evolutionary rates.These results provide more inspiration for understanding the adaptive evolution of other land plants.