Seminars

The newly discovered phytohormones, strigolactones (SLs), regulate numerous essential growth and developmental processes including branching, leaf senescence, root development, and act as rhizospheric signals for communication with symbiotic fungi and parasitic plants. It has been shown that SL signaling requires three distinct enzymes: D14 α/β hydrolase, F-box MAX2/D3 ubiquitin (Ub) ligase, and SMXLs transcription repressors. SMXLs levels are controlled by MAX2 and the phytohormone receptor D14. Despite these findings, key questions concerning the phytohormone perception and regulation by the conformational dynamics remain unanswered. Here we show that MAX2/D3 has multiple functional states that are determined by distinct structural conformations. We demonstrate biochemically and in planta the key role of MAX2/D3 plasticity in the recruitment of D14, SMXLs, and SL perception. Altogether, this work provides new insights into the regulation phytohormones signaling cascades by the ubiquitin proteasome system in plants.