Role of microRNAs in response to Flavescence dorée infection in Vitis vinifera

Micro(mi)RNAs have fundamental roles in in several developmental processes, in defence responses to biotic and abiotic stresses and in genome stability maintenance through post-transcriptional control of several biological pathway intermediates. In the last 10 years several works analysing small RNAs in grapevine (Vitis spp.) were published and several conserved miRNAs and putative novel miRNAs grapevine-specific were identified. In order to reorganize these data, we produced a database of the entire novel-grapevine miRNA candidates so far identified and it was applied in the analysis of grapevines infected by Flavescence dorée (FD). FD is considered one of the most severe phytoplasma diseases affecting grapevine. The spontaneous, complete and stable remission of the symptoms of FD (recovery) is a phenomenon that may occur in infected grapevines. The analysis of small RNAs from Healthy (H), Recovered (R) and FD-infected (I) grapevine cv Barbera allowed us to highlight as FD alters the expression profile of several miRNAs, both known miRNAs and novel miRNA candidates, including those involved in stress responses and photosynthesis. In particular, conserved miRNAs as miR398, miR399 and miR172, were over-accumulated in I plants, as well as the miRNA candidate vvi_miC1 inducing the down-regulation of its target, Photosystem I reaction center subunit II, involved in the regulation of photosynthesis. These molecular changes suggested the possibility that miRNAs are involved in the response of V. vinifera to FD and in the recovery phenomenon, whose molecular and biological bases are still unclear.