植物Ⅲ型聚酮合酶基因家族的分子进化分析

Molecular Evolution of Plant-specific Type Ⅲ PKS Family

Ⅲ型聚酮合酶(type Ⅲ polyketide synthase,PKSⅢ)广泛存在于细菌、真菌和植物中,目前数据库中已积累了大量的序列资料。为了进一步了解植物Ⅲ型聚酮合酶基因家族的分子进化,以及其作为系统进化研究材料的可能性,选取了75条来自不同植物物种包括苔藓类植物、蕨类植物、裸子植物、单子叶植物和双子叶植物的PKSⅢ蛋白序列,用CLUSTAL X软件对其氨基酸序列进行了比对,并用邻位相接法构建了系统进化树。结果表明,尽管不同来源的PKSⅢ序列表现了很大的差异,但保守结构域CHS-like所包含的主要功能位点半胱氨酸(Cys184)、苯丙氨酸残基(Phe236和Phe286)、组氨酸残基(His335)、天冬酰氨残基(Asn369)在各植物物种中具有很好的保守性;同时发现,在植物PKSⅢ序列中多数的Cys位点均具有较好的保守性,而且蕨类植物PKSⅢ和单子叶植物PKSⅢ在Cys保守位点有很好的相似性;进一步构建分子进化树表明,PKSⅢ基因基本上首先根据功能而聚类,明显地划分为CHSs和non-CHSs两类,其次按照不同的植物物种聚类。

Enzymes of the type Ⅲ polyketide synthase（PKSⅢ） is widely distributed in bacteria,fungi and plants,and a number of PKSIII sequences are included in the searchable databases.To further study the molecular evolution patterns of PKSs and the feasibility of species plant-specific type Ⅲ PKS gene family,in this research,75 PKSIII sequences from moss,ferns,gymnosperms,monocots,dicots were collected from GenBank database.All sequence alignments were performed using program Clustal X.The evolutionary tree was constructed by neighboring-joining method.The amino acid sequence alignment of all plant-specific type Ⅲ PKS sequences confirmed that the key function sites（Cys184,Phe236,Phe286,His335,Asn369） were strictly conserved,and the conserved cysteine sites of ferns and monocots were found to be similar.The constructed evolutionary tree manifested that basically there were two main groups,including CHSs and non-CHSs.Furthermore,moss,ferns,gymnosperms,monocots,dicots of plant-specific type Ⅲ PKS in the respective frames of CHSs and non-CHSs groups also formed independent clade.