蕨类植物叶绿体基因ycf94的分子进化研究

ycf94基因是近年来在叶绿体基因组中新发现的一个基因，在蕨类植物中表现高度保守。该研究共选取94种蕨类植物，在系统发育背景下，对ycf94基因的结构特征、密码子偏好性、进化速率和适应性进化进行分析。结果表明, ycf94基因的密码子偏好性较弱，偏好使用以A/U结尾的密码子，且不同物种间的偏好性存在一定差异。密码子偏好性的形成主要受到突变压的影响，同时也存在其他因素的作用；基于凤尾蕨科和其他蕨类中ycf94基因的结构特征存在区别，对两者的分子替换速率进行了比较，表明颠换率、非同义替换率和ω值间存在显著差异；仅检测出1个正选择位点74A，强烈的负选择作用表明ycf94基因的结构和功能基本趋于稳定。这为蕨类系统发育分析提供了新依据，并提供了解析ycf94基因功能的线索。

Molecular Evolution of Chloroplast Gene ycf94 in Ferns

As a newly discovered chloroplast gene in recent years, ycf94 gene, with length of about 200 bp, is conserved among ferns. However, the origin and function of ycf94 require further investigation. The study was performed on the ycf94 gene sequence of 94 species of ferns, in the phylogenetic background, analyzing codon usage bias, evolution rate and selection pressure. Results showed that the codon bias was weak in ycf94 gene which the 3rd position of codon prefers A/U, variously in closely species. The codon bias was mainly produced by gene mutation. In addition, based on the differences in the structural characteristics of ycf94 between Pteridaceae and other ferns, their evolution rate was compared, suggesting that there were significant difference in transversion rate, nonsynonymous substitution rate and omega. Besides, only one position selection site 74A was detected. The strong negative selection pressure indicated that the function and structure of ycf94 were mostly stabilized. The results provide a new clue of phylogenetic analysis in ferns and functional studies of ycf94 gene.