Involved in seed germination and seedling development. Essential for plant responses to karrikins, a class of butenolide compounds, structurally similar to strigolactones, released from burning vegetation that stimulate seed germination and enhance seedling photomorphogenesis. KAI2 is not required for strigolactone-mediated responses, but MAX2 is necessary for responses to karrikins and strigolactones (PubMed:20864454, PubMed:22357928, PubMed:23142794, PubMed:23301669). Lacks detectable hydrolase activity against karrikin (PubMed:23613584). Karrikin binding induces a conformational change (PubMed:23613584). Weak expression in the cytosol. In young seedlings, expressed in hypocotyls and roots. In adult plants, expressed in rosette leaves, stigma, sepals and silique peduncles and tips. By red light. Increased seed dormancy. Long hypocotyl phenotype under red, far-red, and blue light. Belongs to the AB hydrolase superfamily.