山茶属CHS基因家族的组成和分子进化初探

用PCR方法从4种山茶属(Camellia)(山茶科)(Tlaeaceae)植物的总DNA中分别扩增到CHS基因外显子2的部分序列，经克隆、测序得到16个该基因的序列，这些序列与来自GenBank的该属另一种植物的3个序列及作为外类群的大豆(Glycine max (L)Merr)的2个序列一起进行分析。研究表明，山茶属CHS基因家族在进化过程中已分化为A、B、c三个亚家族，包括A1、A2、A3、B1、B2、C等6类不同的基因成员；其中只有A2类成员为全部被研究的5种植物所共有，而其他5类成员只在部分被研究的植物中发现；所有这些CHS成员具有很高的同源性：在核苷酸水平上同一亚家族内基本上高于90％，不同亚家族间也在78％以上。从推测的氨基酸组成看，山茶属内CHS基因的功能已发生了分化，各类成员的碱基替代率有较大差异；从分子系统发育树和可能的氨基酸组成分析，山茶属具有新功能的基因成员是在经过基因重复后，或是由少数几个位点的突变而成，或是由逐渐积累的突变而形成的。进一步分析认为，该属CHS基因的分化直到近期还在活跃地进行，并且不同种的进化式样有一定的差别，这种不同的进化式样可能是物种形成后受不同环境因素影响而形成的。

Molecular Composition and Evolution of the Chalcone Synthase (CHS) Gene Family in Five Species of Camellia (Theaceae)

The molecular composition and evolution of the chalcone synthase (CHS) gene family from five species in Camellia (Theaceae) are explored in this study. Sixteen CHS exon 2 from four Camellia species were amplified from total DNA by PCR method. Three sequences of the fifth species in Camellia and two sequences of Glycine max as the designated outgroups were obtained from GenBank. Our results indicated that CHS gene family in Camellia was differentiated to three subfamilies (A, B, C) during the evolutionary history with six groups (A1, A2, A3, B1, B2, C). Among them, only group A2 was possessed by all five species in this study. However, the other five groups were detected only in some species of the plants studied. All members of CHS gene family in this study had high sequence similarity, more than 90% among the members in the same subfamily and more than 78% among different subfamilies at nucleotide level. According to the estimated components of amino acids, the function of CHS genes in Camellia had been diverged. The nucleotide substitutions of the different groups were not identical. Based on phylogenetic analyse inferred from sequences of CHS genes and their deduced amino acid sequences, we concluded that the CHS genes with new function in this genus were evolved either by mutations on several important sites or by accumulation of the mutations after the gene duplication. A further analysis showed that the diversification of CHS genes in Camellia still occurred recently, and the evolutionary models were different to some extant among different species. So we assumed that the different evolutionary models resulted from the impacts of variable environmental elements after the events of speciation.