Grapevine CYP734A15 is a brassinosteroid-inactivating cytochrome P450 enzyme

Grapevines (Vitis vinifera) are cultivated worldwide with fruits used for fresh consumption, wine brewing, juice, or raisin production. As a group of plant growth-promoting hormones, brassinosteroids (BRs) play extensive roles in multiple aspects of grapevine-environment interactions. BRs can enhance plant biomass accumulation, disease resistance, and tolerance to abiotic stress. Plant BR homeostasis can be modulated by a conserved cytochrome P450 family CYP734A that specifically inactivate BRs. However, grapevine CYP734As haven't been functionally characterized to date. Here, we cloned CYP734A15 from the popular table/raisin grape cultivar Thompson Seedless and demonstrated its BR-inactivating activity via ectopic expression in Arabidopsis thaliana. CYP734A15 overexpression causes BR-deficient dwarfism in Arabidopsis, which can be rescued by exogenous application of brassinolide (BL), the most biologically active BR found in plants. The BR biosynthetic inhibitor brassinazole (BRZ) can abolish Arabidopsis seedling hypocotyl growth difference between CYP734A15 overexpression lines and mock plants harboring the empty vector. CYP734A15 overexpression also abolishes Arabidopsis seedling photomorphogenic phenotypes in high-fluence-rate white light conditions. Our findings collectively indicate that CYP734A15 is a valid brassinosteroid-inactivating P450 enzyme, which can be a potential genome editing target for elevating endogenous BR levels in grapevine.