The miR390/TAS3/ARF module governs the expression of an LBD transcription factor to regulate nodulation and root architecture in Medicago truncatula

MARIA EUGENIA ZANETTI

Nebraska

Conferencia; SOY2023 INTERNATIONAL CONFERENCE; 2023

Institute of Agriculture and Natural Resources

The microRNA390 targets the Trans-Acting SIRNA3 (TAS3) leading to the production of trans-acting small interference RNAs that subsequently post-transcriptionally repress the mRNAs encoding the Auxin Response Factors (ARF)2, ARF3, and ARF4. This module has been linked to the development of lateral organs in both aerial and underground tissues. Previously, we have shown that the miR390/TAS3/ARFs module mediates the control of lateral roots and symbiotic nodules in legumes. Here, we show that a member of the Lateral Organ Boundaries Domain (LBD) family of transcription factors, designated as MtLBD17/29a, is a target of the miR390/TAS3/ARFs module. Transcriptomic, RT-qPCR and promoter fusion analysis revealed that MtLBD17/29a is induced under symbiotic conditions, whereas no induction was observed in roots overexpressing miR390 or simultaneously silenced in MtARF2, MtARF3 and MtARF4a/b. ChIP-PCR experiments demonstrated that MtARF2 binds to an Auxin Response Element (ARE) present in the MtLBD17/29a promoter activating its expression. Knockdown of MtLBD17/29a reduced the length of primary and lateral roots and increased the density of lateral roots, whereas overexpression of MtLBD17/29a produced the opposite phenotype. Interestingly, both knockdown and overexpression of MtLBD17/29a resulted in a significant reduction in the number of nodules and infection events and impaired the induction of the symbiotic genes Nodulation Signaling Pathway (NSP) 1 and 2, which is reminiscent of the phenotype observed in root simultaneously silenced in MtARF2, MtARF3 and MtARF4a/b. These results demonstrate that MtLBD17/29a is regulated by the miR390/TAS3/ARFs module and a direct target of ARF2, revealing a new lateral root regulatory hub recruited by legumes to act in the root nodule symbiotic program.