Linking the miR390/TAS3 and the nod signaling pathways during the nitrogen-fixing symbiosis.

OBECKER K, BOHNER S, REYNOSO M, BUSTOS P, CRESPI M, BLANCO F, ZANETTI ME.

Buenos Aires

Jornada; XVIII Jornadas Anuales Interdisciplinarias Sociedad Argentina de Biología; 2016

Sociedad Argentina de Biología

MicroRNAs (miRNAs) act as post-transcriptional regulators of gene expression during the development of new organs or in response to environmental stimuli. Under low nitrogen conditions, legume plants establish symbiotic associations with soil bacteria known as rhizobium that results in the development of a new specialized root organ, the nodule. Inside the nodule, rhizobia fix the atmospheric nitrogen into reduced forms that are readily assimilated by the plant. Expression analysis of miRNAs in M. truncatula roots indicated that levels of miR390 decreased at early stages of symbiotic interaction. miR390 targets the non-coding transcript TAS3 and triggers the production of the trans-acting small interference RNAs (tasiRNAs). In turn, these TAS3 derived-tasiRNAs (known as tasiARFs) control the stability of transcripts encoding the Auxin Response Factors ARF2, 3 and 4. Overexpression of the miR390 precursor (OX390) decreased the number of nodules and infection events. On the other hand, expression of a target mimicry of the miR390 (MIM390), which significantly reduced tasiARFs production, increased nodule number and altered the morphology and distribution of the nodules. Analysis of early nodulation marker genes on OX390 roots revels that miR390 pathway prevented the induction of the Nodulation Signaling Pathway 1(NSP1) and NSP2 in response to rhizobial infection, while on MIM390 roots the levels of NSP1/2, NIN, ERN1 were increased. These results suggest that the miR390 pathway regulates the expression of symbiotic genes that are essential for nodulation. Construction of OX390 roots library allow us to characterize the transcriptome changes caused by overexpression of miR390 in early stages of the symbiotic association.