The Statistical Analysis For Aminoacyl-tRNA Synthetases And Their Cognate TRNAs In Plants

Transfer RNA (tRNA) and aminoacyl-tRNA synthetases (aaRS) play an important role in protein biosynthesis process. Under the catalysis of aaRS, the correct amino acid (AA) is joined to the correct tRNA, which guarantees the genetic information’s consistency. The origin of tRNA and aaRS is closely related to the establishment of genetic code and protein synthesis system. In the beginning of life, tRNA is only a RNA minihelix. Modern tRNA structure can be generated by the ligation of two RNA minihelices with appropriate sequence. In RNA world, aaRS is the ribozyme with aminoacylation function, and gradually replaced by protein. Based on the endosymbiosis theory, the mitochondrion develops from proteobacteria while the chloroplast develops from cyanobacteria. Most proteobacteria’ and cyanobacteria’ genes loss or transfer to nucleus during evolution, including tRNA and aaRS.Here we choose11plant species including monocotyledon, dicotyledon, moss and alga. We studied the distribution and evolution of tRNA and aaRS in all species mitochondrion, chloroplast and nucleus. In most photosynthetic plants’chloroplast, all tRNA are encoded by the plastid genome. All plants’mitochondria only have a limited set of tRNA genes, especially Chlamydomonas reinhardtii. To compensate this lack, mitochondria import a variable number of nucleus-encoded tRNA. All aaRS in mitochondrial and chloroplast genome will be lost or transfered to nucleus during evolution. Due to the protein import machinery of mitochondrion and chloroplast, all aaRS need to be imported from cytoplasm. In nuclear genome, tRNA related genes include pseudo genes, SINE, tRNA transferred from organelle and true tRNA. The proportion of SINE and pseudo genes in Zea mays and Vitis vinifera’s nuclear genome is much greater than the proportion in other species. As to every kind of tRNA corresponding to every amino acid, the number of Lys-tRNA related SINE is the most. In all species, the percentage of tRNA transferred from organelle is0.3%(Chlamydomonas reinhardtii)～32.9%(Ricinus communis). The number of true tRNA in nuclear genome is288(Chlamydomonas reinhardtii)～1047(Brassica rapa). The number of tRNA isodecoders is about200except Brassica rapa and Vitis vinifera, which coincides with animals. The closer genetic relationship is, the more tRNA orthologs is. Although people commonly think that the coevolution between tRNA and aaRS strongly exists, I have not found obvious evidence in the current study.