Codon usage by chloroplast gene is bias in Hemiptelea davidii

The base composition of the chloroplast genes is of great interest because they play a highly significant role in the evolutionary development of the plants. Evaluation of the 48 chloroplast protein-coding genes of Hemiptelea davidii showed that the average GC content was about 37.32%, while at the third codon base position alone the average GC content was only 27.80%. The 48 genes were classified into five groups based on the gene function and each group displayed specific codon characteristics. Based on the relative synonymous codon usage analysis, a total of 30 high-frequency codons and 11 optimal codons were identified, most of them ended with A or T. Neutrality plot, ENC-plot and PR2-plot analyses showed that the codon usage bias of the chloroplast genes of H. davidii was greatly influenced by natural selection pressures. Meanwhile, the frequency of codon usage of chloroplast genes among different plant species displayed similarities, with some synonymous codons were preferred to be used in H. davidii. In this study, the codon usage pattern of the chloroplast protein coding genes of H. davidii provides us with a better understanding of the expression of chloroplast genes, and may advice the future molecular breeding programmes.