Karrikins are smoke-derived butenolides that, by stimulating seed germination and enhancing seed responses to light, allow plants to exploit reduced competition for light, water and nutrients after wildfires. By contrast, strigolactones are plant-derived butenolides that regulate shoot and root architecture. In Arabidopsis, responses to both classes of molecule require the F-box protein MAX2, so how are the physiologically distinct responses to karrikins and strigolactones achieved? Here, Mark Waters and colleagues suggest that the answer to this puzzle lies with evolutionary specialization within the DWARF14 superfamily of α/β hydrolases (see ). In rice, strigolactone-dependent inhibition of shoot branching requires DWARF14. The researchers show that, in Arabidopsis, the DWARF14 orthologue AtD14 is necessary for normal strigolactone responses, whereas the AtD14 paralogue KAI2 is required for karrikin responses. Notably, the expression patterns of AtD14 and KAI2 are consistent with the plant’s capacity to respond to specific growth regulators at different developmental stages. Thus, AtD14 and KAI2 define proteins that permit the separate regulation of strigolactone and karrikin signalling by MAX2.
