The uneven distribution of water and nutrients in soil induces the plastic growth and development of plant roots so that plants can flexibly adapt to the complex and variable distribution of nutrients in soil. Lateral root formation and elongation are the key manifestations of root plasticity, and both processes are strictly regulated by auxin.

The team of Ding Zhaojun at Shandong University previously elucidated the key role of MPK14 kinase in auxin-induced lateral root emergence (Mol Plant, 2021): MPK14 promotes lateral root emergence by phosphorylation and degradation of ERF13, a key inhibitor of lateral root development. However, how the phosphorylation “precursor signal” drives ERF13 degradation remains unknown. Recently, Ding's team successfully solved this problem and published a research article titled “MAC3A and MAC3B mediate degradation of the transcription factor ERF13 and thus promote lateral root emergence” in The Plant Cell. This study reveals the molecular mechanism by which auxin clears ERF13 during lateral root emergence through simultaneous activation of MPK14 kinase and MAC3A/3B ubiquitin ligase.

To reveal the degradation mechanism of ERF13 in response to auxin, authors obtained the interacting proteins of ERF13 with IP-MSand focused on the ubiquitin ligases MAC3A and MAC3B. In-depth molecular mechanism analysis showed that although MAC3A/3B could ubiquitinate and degrade ERF13, this process required a necessary prerequisite: MPK14-mediated phosphorylation of ERF13. Further analysis confirmed that MPK14-mediated ERF13 phosphorylation is a key signal that “forces” ERF13 to recruit MAC3A/3B and cause its degradation. In addition, the authors found that auxin not only promoted the transcription ofMAC3A/3B, but also enhanced the protein stability of MAC3A/3B, thereby promoting the protein accumulation of MAC3A/3B during lateral root development and the resulting rapid clearance of ERF13.

Associate Professor Yu Zipeng and Master student Qu Xingzhen from Shandong University are the first authors of this paper, and Professor Ding Zhaojun is the corresponding author. Professor Lv Bingsheng from Qingdao Agricultural University, Dr.Yu Qianqian from Liaocheng University, and Dr.Li Xiaoxuan and Dr.Sui Jiaxuan from Shandong University participated in the research. Sincere thanks to Professor Li Shengjun (Qingdao Institute of Bioenergy and Bioprocess Technology) for his selfless gift of plant materials, and Professor Bai Mingyi (Shandong University) for his strong support of rBiFC vectors. This research was jointly supported by the National Natural Science Foundation of China and the Taishan Scholars Special Fund of Shandong Province.