WAV E3 ubiquitin ligases mediate degradation of IAA32/34 in the TMK1-mediated auxin signaling pathway during apical hook development
Junli Wang, Ming Wang, Li Zhang, You-Xia Li, Jingjing Li, Yuyang Li, Zuo-Xian Pu, Danyang Li, Xing-Nan Liu, Guo Wang, Dong‐Wei Di, Xiaofeng Li, Guang‐Qin Guo, Lei Wu
Abstract
Auxin regulates plant growth and development through downstream signaling pathways, including the best-known SCF TIR1/AFB -Aux/IAA-ARF pathway and several other less characterized “noncanonical” pathways. Recently, one SCF TIR1/AFB -independent noncanonical pathway, mediated by Transmembrane Kinase 1 (TMK1), was discovered through the analyses of its functions in Arabidopsis apical hook development. Asymmetric accumulation of auxin on the concave side of the apical hook triggers DAR1-catalyzed release of the C-terminal of TMK1, which migrates into the nucleus, where it phosphorylates and stabilizes IAA32/34 to inhibit cell elongation, which is essential for full apical hook formation. However, the molecular factors mediating IAA32/34 degradation have not been identified. Here, we show that proteins in the CYTOKININ INDUCED ROOT WAVING 1 (CKRW1)/WAVY GROWTH 3 (WAV3) subfamily act as E3 ubiquitin ligases to target IAA32/34 for ubiquitination and degradation, which is inhibited by TMK1c-mediated phosphorylation. This antagonistic interaction between TMK1c and CKRW1/WAV3 subfamily E3 ubiquitin ligases regulates IAA32/34 levels to control differential cell elongation along opposite sides of the apical hook.