Auxin Response Factor 2 (ARF2), ARF3 and ARF4 mediate both lateral root and nitrogen fixing nodule development in Medicago truncatula

HOBECKER, KAREN; BLANCO, FLAVIO A.; KIROLINKO CRISTINA; ZANETTI MARÍA EUGENIA

Modalidad Virtual

Congreso; Plant Biology 2020 Worldwide Summit; 2020

American Society of Plant Biology

AUXIN RESPONSE FACTORS (ARFs) constitute a large family of transcription factors that mediate auxin-regulated developmental programs in plants. ARF2, ARF3 and ARF4 transcripts are post-transcriptionally regulated by the microRNA390 (miR390)/Trans-Acting Short interference RNA 3 (TAS3) pathway through the action of TAS3 derived transacting-small interfering RNAs (ta-siRNA). Previous results have shown that constitutive activation of the miR390/TAS3 pathway promotes lateral root growth but impairs nodule organogenesis and infection by rhizobia during the nitrogen fixing symbiosis established between Medicago truncatula and its partner Sinorhizobium meliloti. However, the involvement of the targets of the miR390/TAS3 pathway, i.e. ARF2, ARF3 and ARF4, in root development and establishment of the nitrogen fixing symbiosis remained unexplored. Here, we provide evidences that simultaneous knock-down of ARF2, ARF3 and ARF4 or mutation in ARF4a altered root architecture, causing a reduction in primary and lateral root length, but increasing lateral root density. Promoter-reporter fusions showed that expression of both ARF3 and ARF4 was associated with lateral root development; however, only ARF4 promoter was active in developing nodules. In addition, up-regulation of ARF2 and ARF4 mRNAs in response to rhizobia depends on Nod Factor perception. Roots with reduced levels of ARF2, ARF3, and ARF4, as well as arf4 mutant plants exhibited reduced nodulation and impaired infection events. Taken together, our results suggest that ARF2, ARF3 and ARF4 are common key players of the morphogenetic programs that control root development and the formation of nitrogen fixing nodules.