Development of a chemical inhibitor of auxin metabolism and agonists for the receptors of strigolactone and karrikin

Abstract

Auxin plays multiple roles in plant growth and development. The auxin concentrations need to be strictly regulated by its biosynthesis, transport, and metabolism in a suitable manner for the plant parts, organs, and developmental events. I developed a chemical inhibitor of GH3 enzymes that catalyze the conjugation reaction of IAA, a dominant endogenous auxin, with amino acid and transform IAA into inactive form. This inhibitor, named Kakeimide (KKI), suppresses auxin metabolism and accumulates endogenous IAA. Endogenous IAA amount in Arabidopsis roots was increased twofold in 10 minutes by treatment of KKI. This result suggests that endogenous IAA is continuously synthesized and metabolized in a 10-minute turnover time. Strigolactone (SL) has been known as a plant hormone that suppresses axillary shoot branching, and its receptor D14 and signaling mechanism have been elucidated. The homological receptor of D14, HTL/KAI2, receives unidentified hormone-like endogenous compounds called KL. HTL/KAI2 mediates the signaling stimulated by karrikins derived from burnt plant material. I developed agonists of SL receptors to mimic plant hormonal action and the structure-activity relationships study elucidated the target preferences of derivatives. Then, I developed agonists of KL receptors with structural modification from the D14 agonist to investigate the biological roles of HTL/KAI2 receptor.