Abstract
Aminoacyl-tRNA synthetases (aaRSs) play essential roles in protein translation. In addition, numerous aaRSs (mostly in vertebrates) have also been discovered to possess a range of non-canonical functions. Very few studies have been conducted to elucidate or characterize non-canonical functions of plant aaRSs. A genome-wide search for aaRS genes in Arabidopsis thaliana revealed a total of 59 aaRS genes. Among them, asparaginyl-tRNA synthetase (AsnRS) was found to possess a WHEP domain inserted into the catalytic domain in a plant-specific manner. This insertion was observed only in the cytosolic isoform. In addition, a long stretch of sequence that exhibited weak homology with histidine ammonia lyase (HAL) was found at the N-terminus of histidyl-tRNA synthetase (HisRS). This HAL-like domain has only been seen in plant HisRS, and only in cytosolic isoforms. Additionally, a number of genes lacking minor or major portions of the full-length aaRS sequence were found. These genes encode 14 aaRS fragments that lack key active site sequences and are likely catalytically null. These identified genes that encode plant-specific additional domains or aaRS fragment sequences are candidates for aaRSs possessing non-canonical functions.
Highlights
Aminoacyl-tRNA synthetases play a central role in protein synthesis in all organisms.The activation of amino acids and attachment to tRNAs comprise the canonical functions of aaRSs.Some aaRSs in higher eukaryotes have been found to possess non-canonical functions and to be involved in numerous cellular processes [1]
These non-canonical functions are often exhibited through species-specific appended domains found among aaRSs, which seem to have been added late in evolution. The advantages of such single genes with multiple functions may include the acquisition of higher-order functions with minimal genetic resources. Such species-specific domains possessing potential non-canonical functions include the WHEP domain, a helix-turn-helix domain named after aaRSs (tryptophanyl-tRNA synthetase (TrpRS), histidyl-tRNA synthetase (HisRS), and glutamyl-prolyl-tRNA synthetase (GluProRS)) that harbor this domain and glutathione S-transferase (GST) domains
A. thaliana aaRS genes were retrieved from The Arabidopsis Information Resource (TAIR) database by annotation searches and BLASTp homology searches with previously identified Arabidopsis aaRS sequences as query
Summary
Aminoacyl-tRNA synthetases (aaRSs) play a central role in protein synthesis in all organisms. These non-canonical functions are often exhibited through species-specific appended domains found among aaRSs, which seem to have been added late in evolution The advantages of such single genes with multiple functions may include the acquisition of higher-order functions with minimal genetic resources. Alternative splicing can generate numerous fragmented transcripts, many of which do not contain a full catalytic domain and are catalytically null [6] These splice variants (SVs) have been shown to participate in numerous biological processes in humans. A number of characterized aaRS mutants impair particular developmental processes, but do not impair global protein synthesis, which is generally lethal [12,13,14,15,16,17] These observations suggest that aaRSs in plants may have specific functions other than tRNA aminoacylation. During the course of our studies, we noticed that the plant genome contains numerous fragmented aaRS sequences, many of which lack catalytic domains
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