microRNA390 and TAS3-derived tasiRNAs regulate the development of nitrogen fixing nodules in the model legume Medicago truncatula

HOBECKER KAREN; REYNOSO MAURICIO ALBERTO; BUSTOS PÍLAR; CRESPI MARTÍN D; BLANCO FLAVIO ANTONIO; ZANETTI MARÍA EUGENIA

Chascomús

Congreso; XV jornadas anuales de la sociedad argentina de biología; 2013

The development of nitrogen fixing nodules depends on the activation of two highly coordinated genetic programs in leguminous plants: the nodule organogenesis and the rhizobial infection. MicroRNAs (miRNAs) have emerged as major post-transcriptional regulators of gene expression during development or in response to environmental stimuli. In a previous work, we have identified miRNAs that change their abundance in roots of the model legume Medicago truncatula at early stages of its interaction with Sinorhizobium meliloti. One of these miRNAs, the miR390, dramatically decreased (about 80%) at early stages of the symbiotic interaction. miR390 targets the non-coding RNA TAS3 and triggers the production of the trans-acting small interference RNAs (tasiRNAs). In turn, TAS3-derived tasiRNAs control the stability or translatability of transcripts encoding the Auxin Response Factors ARF2, 3 and 4. Concomitantly with the change on miR390 abundance, inoculation with S. meliloti lead to a decrease in tasiRNA production and a higher accumulation of ARF2 3 and 4 transcripts. Overexpression of a precursor of miR390 resulted in a reduction in the number and size of the nodules, as well as in the number of infection events. On the other hand, expression of a mimicry (MIM390), which sequestrates miR390 blocking its action on TAS3 transcript and reducing tasiRNAs levels, increased the number of nodules; but affected negatively the size of the nodules and the number of infection events. These results suggest that the miR390 and tasiRNAs pathway is involved in the fine-tune regulation of nodule development and rhizobial infection in M. truncatula.