杨树派间不同种的遗传密码子使用频率分析

遗传密码子的简并性特征造成了不同物种使用的密码子存在偏爱性。了解不同物种的密码子使用特点,可以为外源基因导入过程中的基因改造提供依据,从而实现外源基因的高效表达。杨树是世界上广泛栽培的重要造林树种之一,已经成为林木基因工程研究的模式植物。本研究采用高频密码子分析法,对美洲山杨P.tremuloides,毛白杨P.tomentosa,美洲黑杨P.deltoids和毛果杨P.trichocarpa 4种杨树的蛋白质编码基因序列(CDS)进行了分析,计算出了杨树同义密码子相对使用频率(RFSC),确定了4种杨树的高频率密码子,发现虽然不同种类的杨树密码子使用上有一些差别,但是偏爱密码子的差别却很小,共性的密码子占绝大多数。仅有Pro,Thr和Cys等少数几个氨基酸的偏爱密码子有差别。这种“共性”提示我们,用不同种的杨树中任何一种杨树的偏爱密码子所设计的外源基因在其他杨树中也可以使用。

Analysis of Codon Usage Between Different Poplar Species

Codon usage is the selective and nonrandom use of synonymous codons to encode amino acids in genes for proteins.The analysis of codon usage may improve the understanding of codon preferences between different species and allow to rebuild the codons of exogenous genes to increase the expression efficiency of exogenous genes.Here,codon DNA sequence(CDS)of four poplar species,including Populus tremuloides Michx.,P.tomentosa Carr.,P.deltoides Marsh.,and P.trichocarpa Torr.&Gray.,is used to analyze the relative frequency of synonymous codon(RFSC).High-frequency codons are selected by high-frequency(HF) codon analysis.The results indicate that the codon usage is common for all four poplar species and the codon preference is quite similar among the four poplar species.However,CCT encoding for Pro,and ACT coding for Thr are the preferred codons in P. tremuloides and P.tomentosa,whereas CCA coding for Pro,and ACA coding for Thr are preferred in P.deltoides and P.trichocarpa. The codons such as TGC coding for Cys,TTC coding for Phe,and AAG coding for Lys,are preferred in the poplar species except P. trichocarpa.GAG coding for Glu is preferred only in P.deltoides,while the other three poplar species prefer to use GAA.The commonness of preferred codon allows exogenous gene designed by the preferred codon of one of the different poplar species to be used in other poplar species.