-independent transcriptional responses to GR24 in roots.

Strigolactones (SLs) and smoke-derived Karrikins (KARs) are structurally similar butenolide compounds that control distinct aspects of plant development. They are perceived by two closely related α/β hydrolases D14 and KAI2, respectively. Responses to both molecules involve the F-box protein MAX2 that participates in the Skp1-Cullin-F-box (SCF) complex, which ubiquitylates developmental regulators of the SMXL family to mark them for degradation by the 26S proteasome, enabling SL and KAR responses. Current research on SL and KAR signaling uses the synthetic molecules GR24, KAR and KAR for pharmacological treatments. In a previous microarray analysis, we observed transcriptional activation in response to GR24 in seedling roots. We retested transcript accumulation of selected genes by quantitative PCR in the wild type and the mutant, and found that surprisingly, a number of them respond to GR24 in a -independent manner, and also respond in roots of and double mutants. Thus, the synthetic compounds induce transcriptional responses independent of their perception by the canonical receptor complex.