S-nitrosylation of Aux/IAA protein represses auxin signaling

ABSTRACTAuxin plays crucial roles in nearly every aspect of plant growth and development. Auxin signaling activation is mediated through degradation of Auxin/INDOLE-3-ACETIC ACID (Aux/IAA) family. Nitric oxide (NO) regulates diverse cellular bioactivities through S-nitrosylation of target protein at specific cysteine residues. NO-auxin interplay has an important role in regulation plant growth. However, little is known about the molecular mechanism of how NO effects Aux/IAA proteins stability. Here we show that NO negatively regulates the IAA17 protein stability to repress auxin signaling. We found that NO directly inhibits IAA17 protein degradation. S-nitrosylation of IAA17 at Cys-70 represses the TIR-IAA17 co-receptor interaction to attenuate auxin responsiveness. Our data suggest a model in which S-nitrosylation of IAA17 at Cys-70 negatively regulates auxin signaling to effect plant development, providing a mechanism for redox-phytohormones networks.