title: Divergent Alanyl-tRNA Synthetase Genes of Vanderwaltozyma polyspora Descended from a Common Ancestor through Whole-Genome Duplication Followed by Asymmetric Evolution.
abstract: Cytoplasmic and mitochondrial forms of a eukaryotic aminoacyl-tRNA synthetase (aaRS) are generally encoded by two distinct nuclear genes, one of eukaryotic origin and the other of mitochondrial origin. However, in most known yeasts, only the mitochondrial-origin alanyl-tRNA synthetase (AlaRS) gene is retained and plays a dual-functional role. Here, we present a novel scenario of AlaRS evolution in the yeast Vanderwaltozyma polyspora. V. polyspora possesses two significantly diverged AlaRS gene homologues, one encoding the cytoplasmic form and the other its mitochondrial counterpart. Clever selection of transcription and translation initiation sites enables the two isoforms to be localized and thus functional in their respective cellular compartments. However, the two isoforms can also be stably expressed and function in the reciprocal compartments by insertion or removal of a mitochondrial targeting signal. Synteny and phylogeny analyses revealed that the AlaRS homologues of V. polyspora arose from a dual-functional common ancestor through whole-genome duplication (WGD). Moreover, the mitochondrial form had higher synonymous (1.6-fold) and nonsynonymous (2.8-fold) substitution rates than did its cytoplasmic counterpart, presumably due to a lesser constraint imposed on components of the mitochondrial translational apparatus. Our study suggests that asymmetric evolution confers the divergence between the AlaRS paralogues of V. polyspora.
authors.affiliation: Department of Life Sciences, National Central University, Jungli, Taiwan.
authors.forename: Chia-Pei
authors.initials: CP
authors.lastname: Chang
authors.affiliation: Department of Life Sciences, National Central University, Jungli, Taiwan.
authors.forename: Chih-Yao
authors.initials: CY
authors.lastname: Chang
authors.affiliation: Department of Life Sciences, National Central University, Jungli, Taiwan.
authors.forename: Yi-Hsueh
authors.initials: YH
authors.lastname: Lee
authors.affiliation: Institute of Bioinformatics and Systems Biology, National Chiao Tung University, Hsin-Chu, Taiwan.
authors.forename: Yeong-Shin
authors.initials: YS
authors.lastname: Lin
authors.affiliation: Department of Life Sciences, National Central University, Jungli, Taiwan dukewang@cc.ncu.edu.tw.
authors.forename: Chien-Chia
authors.initials: CC
authors.lastname: Wang
mesh_terms: D000412:Alanine-tRNA Ligase / Q000032:analysis / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D019143:Evolution, Molecular; D020440:Gene Duplication; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D010802:Phylogeny; D004718:Saccharomycetales / Q000737:chemistry / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*
chemical_list: D000412:Alanine-tRNA Ligase