Evidence of multifaceted functions of codon usage in translation within the model beetle Tribolium castaneum.

Synonymous codon use is non-random. Codons most used in highly transcribed genes, often called optimal codons, typically have high gene counts of matching tRNA genes (tRNA abundance) and promote accurate and/or efficient translation. Non-optimal codons, those least used in highly expressed genes, may also affect translation. In multicellular organisms, codon optimality may vary among tissues. At present, however, tissue specificity of codon use remains poorly understood. Here, we studied codon usage of genes highly transcribed in germ line (testis and ovary) and somatic tissues (gonadectomized males and females) of the beetle Tribolium castaneum. The results demonstrate that: (i) the majority of optimal codons were organism-wide, the same in all tissues, and had numerous matching tRNA gene copies (Opt-codon(up arrow tRNAs)), consistent with translational selection; (ii) some optimal codons varied among tissues, suggesting tissue-specific tRNA populations; (iii) wobble tRNA were required for translation of certain optimal codons (Opt-codon(wobble)), possibly allowing precise translation and/or protein folding; and (iv) remarkably, some non-optimal codons had abundant tRNA genes (Nonopt-codon(up arrow tRNAs)), and genes using those codons were tightly linked to ribosomal and stress-response functions. Thus, Nonoptcodon(up arrow tRNAs) codons may regulate translation of specific genes. Together, the evidence suggests that codon use and tRNA genes regulate multiple translational processes in T. castaneum.