Brassinosteroid-related acyltransferase1 mediates crosstalk between gibberellin signaling and brassinosteroids to regulate primary seed dormancy.

RGL2:DOF6 protein complex enhances BAT1 expression, which promotes primary seed dormancy in Arabidopsis, likely by inhibiting brassinosteroid biosynthesis. Hence, BAT1 acts as a novel gibberellin and brassinosteroid signaling crosstalk intermediate. A transcription factor complex including RGA-LIKE2 (RGL2) and DNA-BINDING ONE ZINC FINGER6 (DOF6) helps enforce primary seed dormancy. To elucidate the underlying mechanism by which the RGL2:DOF6 complex can enhance primary seed dormancy, we initiated a search for the downstream targets of this transcription complex. Using RNA sequence analysis, BRASSINOSTEROID-RELATED ACYLTRANSFERASE1 (BAT1) was identified to be a downstream target gene of the RGL2:DOF6 complex. Various genetic and molecular analyses were conducted using the mutant and overexpression lines. BAT1 is a known modulator of endogenous brassinosteroid (BR) levels. We observed that freshly harvested, unstratified bat1 mutant seeds germinated earlier, while BAT1 overexpression lines germinated later than the wild-type (WT) seeds. Consistently, dry-storage and cold-stratification of WT seeds, treatments that help to break dormancy, caused suppression of BAT1 expression levels. RT-qPCR and luciferase-based transcriptional assays showed that BAT1 expression could be enhanced by DOF6 in combination with RGL2 (i.e., by RGL2:DOF6 complex), a gibberellin (GA) signaling factor. BAT1 expression was also enhanced in abscisic acid (ABA)-treated seeds, which exhibit delayed germination. The function of BAT1 in sustaining primary seed dormancy is likely to occur via inhibition of BR biosynthesis because DOF6 overexpression seeds show suppression of BR biosynthetic genes (DWF1 and ROT3). Overall, these observations reveal that BAT1 serves as a crosstalk intermediate between BR and GA signaling pathways as one of the mechanisms in the regulation of primary seed dormancy.