microRNA390 regulates lateral root growth and nodule formation in the model legume Medicago truncatula

REYNOSO, MAURICIO; HOBECKER, KAREN; BUSTOS, PILAR; CRESPI, MARTÍN; BLANCO, FLAVIO; ZANETTI, MARÍA EUGENIA

Mendoza

Congreso; XLVIII Reunión anual de la Sociedad Argentina de Investigaciones Bioquímicas; 2012

microRNA390  regulates lateral root growth and nodule formation in the model legume Medicago truncatula   Mauricio Alberto Reynoso1, Karen Hobecker1,  Pilar Bustos2, Martín Crespi2, Flavio Antonio Blanco1 and María Eugenia Zanetti1   1Instituto de Biotecnología Y Biología Molecular, FCE-UNLP CCT-CONICET.  2Institut des Sciences du Végétal, CNRS, Gif sur Yvette, France. E-mail: ezanetti@biol.unlp.edu.ar.TE: 54 221 4250497 ext 61     MicroRNAs have emerged as major regulators of post-transcriptional gene expression during development or in response to environmental stimuli. Plant roots are able to adapt to the local environment to maximize water and nutrient acquisition by adjusting their developmental programs (e.g. forming new lateral roots). Under low nitrogen availability, roots of leguminous plants establish a symbiotic association with soil bacteria called rhizobia, which results in the formation of a highly specialized lateral root organ, the nodule. In our laboratory, we have identified several microRNAs that change their abundance in roots of the model legume Medicago truncatula at early stages of its symbiotic interaction with Sinorhizobium meliloti. One of this miRNAs, mi390, dramatically decreased (~80%) in inoculated roots as compared to non-inoculated ones. miR390 targets the non-coding RNA TAS3 and triggers the production of the trans-acting small interference RNAs tasiARFs. Formation of tasiARFs occurs via the so called "two hits" model of dual miRNAs target site in the TAS3 transcript. In turn, tasiARFs control the stability or translatability of transcripts encoding the Auxin Regulated transcription Factors ARF2, 3 and 4. Consistent with the decrease on miR390 abundance, inoculation with S. meliloti led to an increase on the abundance of TAS3 precursor, a decrease  in tasiARFs production and higher accumulation of  ARF2,3 and 4 transcripts. Overexpression of the miR390 precursor in hairy roots of M. truncatula resulted in an increase of lateral root length, and a reduction in the number of nodules developed by the rhizobia. These results suggest that miR390 might be part of a pathway that negatively controls symbiotic nodule organogenesis, but promotes lateral root growth in M. truncatula.                                                                                          This work was supported by ANPCyT (PICT 2007-00095).