中文摘要：

核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco,EC 4.1.1.39）是植物参与光合作用的关键酶,其大亚基由叶绿体rbcL基因编码。为深入理解凤尾蕨科植物对干旱生境的分子适应机制,本研究以53种凤尾蕨科旱生植物的rbcL基因为对象,展开适应性进化和共进化研究。采用位点间可变ω比值模型以及SLAC、REL和FEL等方法进行的适应性进化分析显示：在氨基酸水平上共有15个正选择位点（66S、84E、139L、235G、245I、252A、273Y、295K、296N、299M、307G、330E、349S、365F、404A）,其中位点245I、252A和273Y对维持Rubisco功能起重要作用。共进化分析共鉴定出2组共进化位点,分别由139L、273Y、295K和273Y、295K、349S组成,这些氨基酸位点间的共进化方式与蛋白质的疏水性和分子量都显著相关。以上结果一方面支持基于ω比值检验DNA编码序列发生适应性进化的有效性,另一方面也提示凤尾蕨科植物对干旱生境的适应可能与rbcL基因的适应性进化有关。

英文摘要：

Ribulose 1,5-bisphosphate carboxylase /oxygenase（Rubisco,EC 4.1.1.39） is the key photosynthesis enzyme in plants,whose large subunit is encoded by the chloroplast rbcL gene.To better understand the molecular adaption mechanisms of Pteridaceae ferns acclimating to xeric habitats,both adaptive evolutionary and coevolutionary analyses were performed on the rbcL gene sequences of 53 Pteridaceae xeric fern species.The adaptive evolutionary analyses under variable ω ratio sites as well as SLAC,REL and FEL methods indicated that 15 amino acid residues（66S,84E,139L,235G,245I,252A,273Y,295K,296N,299M,307G,330E,349S,365F and 404A） were positively selected.In particular,three sites（245I,252A and 273Y） played an important role in maintaining enzymatic function.The subsequent coevolutionary analysis revealed two groups of coevolutionary residues（139L,273Y and 295K） and（273Y,295K and 349S）,which showed that their coevolutionary patterns were significantly related to protein hydrophobicity and molecular weight.This research consolidated that evolutionary models using ω as an indicator of selective pressure provide valuable analysis of the adaption of protein encoding sequences.In addition,this study also demonstrated that Pteridaceae ferns may respond to xeric habitats by adaptively modifying the rbcL gene.