The analysis of coded characters of crop chloroplast genes is benefit to the genetic engineering design of chloroplast, and the efficient and stable expression of exotic genes in recipient crops. In this study, the codon usage bias of genes encoded by chloroplast DNA in 7 field crops were analyzed by means of several softwares. Results showed that there was little difference among the characters of chloroplast-coded genes among the 7 crops, which held a higher content of A and lower content of G and C. However, there were significant differences in the base composition of the third codon. The codons in the 3 dicotyledon crops were preferred to end with C,and second with T,while the other 4 gramineous crops preferred the codons ended with prior T,and second with C. There were 26 preferable codons used in the 4 gramineous crops and 25 in the 3 dicotyledon plants, among which 22 codons were totally same between the 2 kinds of crops. The cluster analysis based on RSCU value showed that the codon usage bias in the genes encoded by chloroplast was related to the plant species, indicating that the cluster analysis of RSCU in chloroplast genes could be used as a complementary method for the systematic developmental analysis.%研究作物叶绿体蛋白编码基因的编码特点,对指导农作物的叶绿体基因工程研究设计,促进外源基因在受体作物中的高效、稳定表达具有重要作用.为此,综合运用了多种分析软件,对7种大田作物的叶绿体蛋白编码基因进行分析.结果表明:叶绿体蛋白编码基因的总碱基构成在7种作物中差异不大,都是A含量最高,而G,C的含量较低；但在密码子第3位的碱基构成上却有明显差别,3种双子叶作物偏爱以C,T结尾的密码子,而禾本科的4种作物则偏爱以T,C结尾的密码子；RSCU(同义密码子的相对使用度)值显示出禾本科作物有26个密码子具有偏好性,而双子叶作物有25个密码子具有偏好性,但二者之间有22个相同的偏好性密码子.基于RSCU值的聚类结果显示,植物的密码子偏好性具有种族特征,表明基于叶绿体蛋白编码基因的密码子使用特性的聚类结果可以作为系统发育分析的重要补充.
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