Water deficit down-regulates miR398 and miR408 in pea (Pisum sativum L.).

MicroRNAs (miRNAs), recently recognized as important regulator of gene expression at posttranscriptional level, have been found to be involved in plant stress responses. The observation that some miRNAs are up- or down regulated by stress implies that they could play vital roles in plant resistance to abiotic and biotic stress. We investigated the effect of water stress treatment during 10 days on expression of conserved miRNAs-miR398a/b and miR408 in pea plants. This time frame reflects the changes as close as possible to the changes where water stress causes visible effects under field condition. It was observed that dehydration strongly down regulates the expression of both miR398a/b and miR408 in pea roots and shoots. The down-regulation of miR398a/b and the up-regulation of potential target genes - copper superoxide dismutase, CSD1, highlight the involvement of this miRNA in pea stress response. To the contrary, the mRNA level of cytochrome c oxidase subunit 5 (COX5b) did not change in roots and shoots of water-stressed plants, compared to control (well) hydrated plants. This suggests that COX5b is not the target of miR398, or that its expression is regulated by some other mechanism. P1B-ATPase expression increased during water deficit only in the shoots of pea; in the roots there were no changes in expression. Our results help to understand the possible role of investigated miRNAs and their contribution to pea capacity to cope with water deficit.