Tissue and regional expression patterns of dicistronic tRNA-mRNA transcripts in grapevine (Vitis vinifera) and their evolutionary co-appearance with vasculature in land plants

Abstract

Transfer RNAs (tRNA) are crucial adaptor molecules between messenger RNA (mRNA) and amino acids. Recent evidence in plants suggests that dicistronic tRNA-like structures can also act as mobile signals for mRNA transcripts to move between distant tissues. Co-transcription is not a common feature in the plant nuclear genome and, in the few cases where polycistronic transcripts have been found, they include the expression of non-coding RNA species such as small nucleolar RNAs and microRNA clusters. It is not known, however, the extent to which dicistronic transcripts of tRNA and mRNAs are expressed in field-grown plants, or the factors contributing to their expression. To address these questions, we analysed tRNA-mRNA dicistronic transcripts in the major horticultural crop grapevine (Vitis vinifera) using a novel pipeline developed to identify dicistronic transcripts from high-throughput RNA sequencing data. We identified dicistronic tRNA-mRNA in grapevine leaf and berry samples from 22 commercial vineyards covering six sub-regions of the Barossa wine growing region, Australia. Of the 124 tRNA genes that were expressed in both tissues, 18 tRNA were expressed forming part of 19 dicistronic tRNA-mRNA molecules. The presence and the abundance of dicistronic molecules was tissue and geographic sub-region specific. In leaf tissue, the expression patterns of dicistronic tRNA-mRNAs significantly correlated with tRNA expression, suggesting that transcriptional regulation of their expression might be linked. We also found evidence of evolutionary conservation of dicistronic candidates in grapevine, and previously reported dicistronic transcripts in Arabidopsis, indicating a syntenic genomic arrangement of tRNAs and protein coding genes between species.

Deep origin and gradual evolution of transporting tissues: Perspectives from across the land plants

“…The extensive incorporation of mobile signals in the development of transporting tissues seems less pronounced in bryophytes and seed-free tracheophytes. Plasmodesmata seem to be differently wired in bryophytes and ferns ( Ligrone and Duckett, 1998 ; Imaichi and Hiratsuka, 2007 ; Imaichi et al, 2018 ), while tRNA and mRNA mobile signals seem absent from bryophytes ( Fabres et al, 2021 ). Possibly, mobile signals and vascular tissue development co-evolved; facilitating the increasing complexity of tracheophyte vascular tissues compared to the less elaborate bryophyte conductive tissues.…”