Abstract: In this study, Codon W and EMBOSS tools were adopted to determine relevant parameters, including relative synonymous codon usage (RSCU), effective number of codons (ENc), codon adaptation index (CAI), and base composition, of 68Papaver somniferumL. O-methyltransferase (PsOMT) genes. Furthermore, neutrality plot, ENc-plot, and PR2-plot were used to identify the predominant factor shaping codon usage patterns. The results showed weak codon usage bias, and the low expression level of PsOMT genes, with the average ENc values of 48.94 and average CAI values of 0.22. The average GC content of 0.40 exhibited a descending pattern of GC1s>GC2s>GC3s with an uneven distribution, suggesting preferential usage of Adenine (A) / Uracil (U)-ending codons, especially at the terminal codon. The results of neutrality plot, ENc-plot, and PR2-plot indicated that natural selection functioned as the predominant force shaping codon usage patterns. Among PsOMT genes, there were 17 optimal codons with A/U as the terminal codon, of which AGA was the most frequent. These findings provide insights for codon optimization of PsOMT genes, thereby facilitating the enhanced synthesis ofP. somniferumL. alkaloid through genetic engineering.

Key words: codon usage bias, O-methyltransferase;Papaver somniferumL., optimal codon