Transcriptome analysis and functional identification of transfer RNA-derived fragments in grape leaves exposed to UV-C radiation.

Transfer RNA-derived fragments (tRFs) are noncoding small RNAs derived from transfer RNAs (tRNAs) in microorganisms, animals and plants. In plants, tRFs are known to respond to environmental stimuli, including heat, oxidative stress and UV radiation; however, their specific functions in horticultural plants, such as grapevine, remain poorly understood. In this study, we used RNA-seq to identify differentially expressed genes (DEGs) in grape leaves exposed to UV-C radiation. A total of 1329 and 8055 of genes were differentially expression after 1 and 6 h of UV-C treatment, respectively. We identified a large number of secondary metabolism-related genes in the DEGs, including genes involved in stilbene and flavonoid biosynthesis. Noticeably, the stilbene biosynthesis-related gene was induced earlier than the other genes in the phenylalanine metabolic pathway. We also conducted small RNA-seq and identified differentially expressed (DE) miRNAs and their targets. To explore whether the tRFs involved in UV-C response, further analysis of the small RNA-seq data revealed 23 down-regulated and 41 up-regulated DE tRFs. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) showed that the target genes of these tRFs are involved in multiple biological processing, including hormone signal transduction and metabolite synthesis. To validate the function of tRFs, tRF39 and tRF45 were selected and overexpressed in tobacco leaves, and the expression levels of their target genes were inhibited. Our study suggests that the tRFs may regulate multiple biological processes in response to UV-C exposure in grapevine. Our findings provide a foundation for further elucidating the regulatory mechanisms of tRFs in horticultural crops.