Regulation of auxin signaling: A key node of plant development and acclimation to stress

Abstract

Auxin has been implicated in developmental switches as well as in transient and dynamic cellular responses during acclimation to abiotic stress. The core components of the auxin signaling machinery mainly involves the F-box TRANSPORT INHIBITOR RESPONSE 1/AUXIN SIGNALING F-BOX PROTEIN (TIR1/AFB) auxin co-receptors, the Auxin/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional repressors, and the AUXIN RESPONSE FACTOR (ARF) transcription factors. In particular, TIR1 and AFBs as part of SCFTIR1/AFB E3 UB-ligase complexes are regulated by multiple post-transcriptional and post-translational mechanisms, resulting in different regulatory layers to auxin perception. We investigated how nitric oxide (NO), through S-nitrosylation of the cysteine (C) residue (C140) of TIR1 and C37 of the scaffold protein ASK1 is involved in SCFTIR1/AFBs assembly impacting on Arabidopsis development. Overexpression of the tir1C140A protein in the tir1-1 background resulted in enhanced tolerance to NaCl-mediated salt stress, while overexpression of TIR1 restores salt sensitivity. In addition, to post-transcriptional regulation, we demonstrated that NaClmediated salt stress induces miR393 expression leading to a concomitant reduction in the levels of the TIR1 and AFB2 receptors and a modulation of antioxidant metabolism. Thus, TIR1/AFBs could be critical node between auxin signaling and specfic redox-associated components in order to coordinate time-specific growth responses during acclimation to salt stress. Taking together our findings provide a functional link to a better understanding of how auxin, NO and miR393 interactions can be integrated and regulated by environmental signals in Arabidopsis plants. From a biotechnological perspective, some challenges through the modulation of auxins are being explored.