2种玉兰属植物叶绿体基因组密码子偏好性分析

利用Codon W、CUSP及R语言等软件对2种玉兰属植物叶绿体基因组密码子的使用偏好性进行分析。结果表明：两者叶绿体基因组密码子的GC含量均为GC₁＞GC₂＞GC₃，说明密码子第3位碱基A/U含量高。大部分有效密码子数（ENC）都在45以上，CAI平均值为0.167，说明密码子偏好性弱。ENC−plot、PR2−plot及中性绘图分析表明GC₁、GC₂与GC₃之间相关性不明显；且第3位碱基使用频率为T > A，G > C，说明2种玉兰属植物叶绿体基因组密码子的偏好形成受到自然选择和基因突变的共同影响，自然选择为主要影响因素。利用相对使用度(RSCU) 、ENC值共筛选出30个最优密码子，大部分以A/U结尾，证明二乔玉兰和日本辛夷2种玉兰属植物叶绿体基因组密码子第3位碱基偏好A/U。

Analysis of Codon Usage Bias(CUB) in the Chloroplast Genomes of 2 Yulania species

This paper analyzed the codon usage in chloroplast genome of 2 Yulania species by Codon W, CUSP and R software. The results showed that the GC content of chloroplast genomes of 2 Yulania species was GC1 > GC2 > GC3, which indicated the content of base A/U at codon 3 was high. The effective number of codons (ENC) of CDS sequences exceeding 45 were more than 80 base pair, and the average CAI value was 0.167, which indicated weak codon bias. The results of ENC−plot, PR2−plot and neutral plot analysis showed that the correlation among GC1, GC2 and GC3 was not significant. And the usage frequency of the third base was T > A, G > C. It indicated that the formation of codon bias in chloroplast genome of 2 Yulania species was affected by natural selection and gene mutation cooperatively, and natural selection is the main affecting factor. According to the relative synonymous codon usage(RSCU)and ENC values, 30 optimal ciphers ending in A/U were selected. It was demonstrated that the codon 3 position in the chloroplast genome of 2 species of Yulania soulangeana and Yulania kobus has an A/U preference.