Conserved and novel miRNAs influence strain preference in the Phaseolus vulgaris-Rhizobium etli nitrogen fixing symbiosis

CASTAINGTS, MELISSE; VILLAGRA, ULISES MANCINI; BLANCO, FLAVIO; ZANETTI, MARÍA EUGENIA

Congreso; XXXII Reunión Argentina XVI Congreso Latinoamericano de Fisiología Vegetal; 2018

Phaseolus vulgaris (common bean) establishes a nitrogen fixing symbiosis with its partner Rhizobium etli. Beans from the Mesoamerican center of genetic diversification exhibited a preference by highly efficient and competitive strains, which is governed by an exchange of signals and the reprogramming of gene expression in both symbionts. MicroRNAs (miRNAs) are endogenous small RNAs that participate in the control of gene expression in eukaryotes, mainly at post-transcriptional level. Here, we used a small RNA-seq approach to identify conserved and novel miRNAs that differentially accumulate in root cells at early stages of a high efficient symbiotic interaction. Conserved miRNAs included miR167a, mi171a and miR390b. Functional analysis of miR390b demonstrated that this miRNA acts as a negative regulator of nitrogen fixing symbiosis in common bean. The analysis of a novel miRNA -designated miR5924- revealed that the mature miR5924 is processed from a stem-loop precursor located in the 5´UTR of a type III RNAse transcript and has a receptor involved in plant defense as the putative target. Overexpression of miR5924 altered strain preference and decreased the outcome of the symbiotic interaction. The role of this miRNAs in the suppression of defense responses required for the successful establishment of the symbiotic interaction will be discussed.