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

Transfer RNAs(tRNA)are crucial adaptor molecules between messenger RNA(mRNA)and amino acids.Recent evidence in plants suggests that dicistronic tRNA-like structures 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 non-coding RNA species,such as small nucleolar RNAs and microRNAs.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.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 leaf and berry samples from 22 commercial vineyards.Of the 124 tRNA genes that were expressed in both tissues,18 tRNA were expressed forming part of 19 dicistronic tRNA–mRNAs.The presence and abundance of dicistronic molecules was tissue and geographic sub-region specific.In leaves,the expression patterns of dicistronic tRNA–mRNAs significantly correlated with tRNA expression,suggesting that their transcriptional regulation might be linked.We also found evidence of syntenic genomic arrangements of tRNAs and protein-coding genes between grapevine and Arabidopsis thaliana,and widespread prevalence of dicistronic tRNA–mRNA transcripts among vascular land plants but no evidence of these transcripts in non-vascular lineages.This suggests that the appearance of plant vasculature and tRNA–mRNA occurred concurrently during the evolution of land plants.

Accumulation of mutations in genes associated with sexual reproduction contributed to the domestication of a vegetatively propagated staple crop,enset

Enset(Ensete ventricosum(Welw.)Cheesman)is a drought tolerant,vegetatively propagated crop that was domesticated in Ethiopia.It is a staple food for more than 20 million people in Ethiopia.Despite its current importance and immense potential,enset is among the most genetically understudied and underexploited food crops.We collected 230 enset wild and cultivated accessions across the main enset producing regions in Ethiopia and applied amplified fragment length polymorphism(AFLP)and genotype by sequencing(GBS)analyses to these accessions.Wild and cultivated accessions were clearly separated from each other,with 89 genes found to harbour SNPs that separated wild from cultivated accessions.Among these,17 genes are thought to be involved in flower initiation and seed development.Among cultivated accessions,differentiation was mostly associated with geographical location and with proximity to wild populations.Our results indicate that vegetative propagation of elite clones has favoured capacity for vegetative growth at the expense of capacity for sexual reproduction.This is consistent with previous reports that cultivated enset tends to produce non-viable seeds and flowers less frequently than wild enset.