MAC3A and MAC3B mediate degradation of the transcription factor ERF13 and thus promote lateral root emergence.

Lateral roots (LRs) increase root surface area and allow plants greater access to soil water and nutrients. LR formation is tightly regulated by the phytohormone auxin. Whereas the transcription factor ETHYLENE-RESPONSIVE ELEMENT BINDING FACTOR13 (ERF13) prevents LR emergence in Arabidopsis (Arabidopsis thaliana), auxin activates MITOGEN-ACTIVATED PROTEIN KINASE14 (MPK14), which leads to ERF13 degradation and ultimately promotes LR emergence. In this study, we discovered interactions between ERF13 and the E3 ubiquitin ligases MOS4-ASSOCIATED COMPLEX 3A (MAC3A) and MAC3B. As MAC3A and MAC3B gradually accumulate in the LR primordium, ERF13 levels gradually decrease. We demonstrate that MAC3A and MAC3B ubiquitinate ERF13, leading to its degradation and accelerating the transition of LR primordia from stages IV to V. Auxin enhances the MAC3A and MAC3B interaction with ERF13 by facilitating MPK14-mediated ERF13 phosphorylation. In summary, this study reveals the molecular mechanism by which auxin eliminates the inhibitory factor ERF13 through the MPK14-MAC3A and MAC3B signaling module, thus promoting LR emergence.