Strigolactone signaling complex formation in yeast: A paradigm for studying hormone-induced receptor interaction with multiple downstream proteins

Strigolactones (SLs) are bioactive carotenoid derivatives which function as signaling molecules to regulate plant architecture, nutrient absorption and communication with other organisms. The a/ss-fold hydrolase, D14, hydrolyzes SLs, and the hydrolysis product activates D14 to bind to downstream signaling partners, including an E3 ubiquitin ligase MAX2 and SMXL6/7/8 proteins. What was not known was whether binding with one downstream partner would alter the affinity of D14 for other binding partners. Here, we developed an efficient yeast four-hybrid (Y4H) detection system and demonstrate that SL induces the interaction of D14 with both SMXL7 and MAX2 in a dose-dependent manner. Moreover, using our newly established yeast four-hybrid system, we found that the SL-induced D14 interaction with SMXL7 was strengthened by MAX2 while SMXL7 weakened the SL-induced D14 interaction with MAX2. Our findings provide novel insights into the regulatory effects of these signaling components and shed light on the molecular mechanism controlling the core SL signaling pathway. Furthermore, the heterologous yeast platform used for investigating SL complex formation has great potential to explore dynamic interactions in other signaling pathways or elucidate the unknown complex formation for biosynthesis of the parent carotenoids of SLs.