Function of a microRNA gene containing an intron in Solanum lycopersicum

Abstract

MicroRNAs (miRNAs) are short single stranded RNA molecules. They are ~21 nucleotide long that are derived from long hairpin structures that result in post transcriptional gene silencing. MiRNA molecules are incorporated into a protein complex called RISC (RNA-induced silencing complex) and take this complex to target mRNA for degradation or inhibition of translation. It has been shown that miRNA molecules and other short RNA molecules intrinsically linked to the regulation of many genes that control the development, growth, and differentiation of plants. In this study, we have characterised a novel tomato miRNAtop14. This miRNA is unusual as its primary transcript (pri-miRNA) contains a ~700nt intron, which is spliced out. MiRNA top 14 has been found to be conserved within the economically important Solanaceae family and among other agriculturally relevant members of the Solanales order, like in sweet potato, while its peculiar intron-split pri-miRNA structure is exclusively kept in the more closely related genera Solanum, Capsicum and Nicotiana. A mRNA cleaved by this miRNA was identified; the mRNA coding for LOW PHOSPHATE ROOT (LPR), a protein, which is involved in the arrest of root growth under phosphate starvation conditions in Arabidopsis. Interestingly, although LPR is widely conserved in plants, included in all the ones harbouring miRNAtop14, LPR cleavage was found to occur only in the three genera where the intron-split pri-miRNA structure is conserved. The current study indicates that MIRs encoded by less canonical loci should be included in future miRNA searches, since they may be producing mature miRNAs with a function, as seen in this investigation. Furthermore, our results suggest that thismiRNA (top14) seems to be involved in plant growth and development as our experiments have indicated that the deletion of MIRtop14 seems to affect the root development. Moreover, as it is mentioned above, during the working on this project the experiments have found a target for top14 so called LOW PHOSPHATE ROOT1 (LPR1) in roots and the analyses by Northern blot have shown a high expression level of this miRNA in roots. Finally, the discovery of this miRNA and the study of it so far have opened up numerous avenues of possible investigation. Further study would indicate how this miRNA functions in the plant.