Novel structures and evolution of tRNA genes: insight into the chloroplast tRNAs of family Sapindaceae

Transfer ribonucleic acids (tRNAs) are small non-coding ribonucleic acids that decode messenger RNA sequences and are directly involved in protein synthesis by carrying amino acids to the ribosome. However, the chloroplast genome needs to better understand tRNAs' phylogeny and evolutionary mechanisms. The present study aimed to delineate the novel structural variations and evolutionary characteristics in the chloroplast genome tRNAs of thirty-six Sapindaceae species. Several novel tRNA structures were identified in the Sapindaceae chloroplast genome. The length of tRNAs ranged from 64 to 93 nucleotides, containing 27–29 anticodons. Pair-wise sequence results showed the conserved nucleotide consensus sequence U-U-C-x-A–x-U in Sapindaceae. The structural analysis revealed that, except for a few tRNAs (tRNA His , tRNA Gly , tRNA Thr , tRNA Phe , tRNA Try , tRNA Met , and tRNA Pro ), all contained a G nucleotide at the 1st position in the acceptor's arm of tRNAs secondary structure. The rate of transition and transversion of tRNAs are Iso-acceptor-specific. Evolutionary analysis revealed that Sapindaceae chloroplast tRNAs might have evolved polyphyletically with a high percentage of gene loss. Phylogenetic analysis revealed that the chloroplast genome's tRNAs evolved from several common ancestors. At the same time, tRNA Val and tRNA Met appear to be the ancestral tRNAs that underwent duplication diversification to give rise to other tRNAs. Our findings will help us understand the evolution of the tRNA and suggest a key role in chloroplast tRNA biology.