Substrate-induced degradation of the a/b-fold hydrolase KARRIKIN INSENSITIVE2 requires a functional catalytic triad but is independent of MAX2

Derived from burnt vegetation, karrikins (KAR) are butenolide chemicals that stimulate seed germination and enhance seedling responses to light. Genetic and biochemical studies have identified KARRIKIN INSENSITIVE2 (KAI2) as a putative karrikin receptor protein (reviewed by Waters et al., 2014). KAI2 is an α/β-fold hydrolase and a paralog of DWARF14 (D14; AtD14 in Arabidopsis), and both possess the conserved catalytic triad of Ser, His, and Asp residues typical of this class of hydrolytic enzymes.