Unequal functional redundancy among B2 Raf-like kinases in the trimethylbutenolide (TMB)-responsive seed dormancy of...

RAF-like kinases (RAFs) play diverse roles across development and environmental adaptation in plants. TES1/RAF12, a B2 RAF in Arabidopsis thaliana, serves as a key regulator of seed germination in response to trimethylbutenolide (TMB), a smoke compound. Given that B2 RAF family members share conserved domains and biochemical activity, we investigated whether B2 RAF members other than TES1 are involved in the TMB-responsive germination. To address this, we examined germination phenotypes of single and high-order mutants of B2 RAFs. Freshly matured raf7 mutant seeds displayed partial TMB resistance during germination, while other raf single mutants, except the tes1 mutant, were indistinguishable from the wild type, suggestive of a role of RAF7 in TMB-responsive germination. Among the B2 raf double mutants, only the raf7raf10 mutant exhibited markedly enhanced TMB resistance during germination, comparable to that of the tes1 mutant. In accordance, TMB-responsive gene expression was severely impaired in the raf7raf10 mutant. These results suggest that RAF7 and RAF10 play a critical role in TMB-responsive germination in a redundant way. Interestingly, a series of B2 raf double mutants displayed differential degrees of redundancy during germination in response to ABA or paclobutrazol, a GA biosynthetic inhibitor. Taken together, these findings suggest that B2 RAFs are not functional equivalents but rather play distinct roles in responses to various stimuli during germination in Arabidopsis thaliana.