Libro de resumenes - The miR390/TAS3/ARF pathway governs expression of an LBD member to regulate root nodule symbiosis and root architecture in Medicago truncatula

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Resumen *

The microRNA390 targets the TAS3 transcript leading to the production of trans-acting small interfering RNAs (tasiRNAs), which in turn post-transcriptionally repress the mRNAs encoding the Auxin Response Factors (ARFs) 2, 3 and 4. This pathway has been involved in the development of lateral organs in both aerial and underground tissues. Previously, we have shown the miR390/TAS3/ARFs pathway mediates the development of lateral roots and symbiotic nodules in legumes. More recently a transcriptomic study of Medicago truncatula miR390 overexpressing roots revealed that a member of the Lateral Organ Boundaries Domain (LBD) family of transcription factors is controlled by this pathway. A phylogenetic analysis revealed that this member of the LBD family is evolutionary related to LBD17 and LBD29 from Arabidopsis, thus we named it as MtLBD17/29. RNA-seq, RT-qPCR and promoter fusion analyses revealed that MtLBD17/29 is induced under symbiotic conditions, but not in miR390 overexpressing roots or in roots that have been silenced in ARF2/3/4. ChIP-PCR experiments demonstrated that MtLBD17/29 is a direct target of MtARF2. Knockdown of MtLBD17/29 produced a significant reduction in the number of nodules and infection events and impaired the induction of the symbiotic genes Nodulation Signalling Pathway (NSP) 1 and 2, reminiscent of the phenotype observed in ARF2/3/4 silenced roots. In addition, knockdown of MtLBD17/29 altered root architecture reducing the length of primary and lateral roots but increasing the density of lateral roots. These results suggest that MtLBD17/29, which has been involved in lateral root development in nonlegume species (i.e., Arabidopsis and tomato), has been recruited in legumes to mediate the root nodule symbiosis, as previously described for other member of the LBD family of transcription factors. Información suministrada por el agente en SIGEVA