BoMYB96 and BoMYB2 positively regulate seed germination by inhibiting the transcription of BoABI5

The bZIP transcription factor ABI5 (Abscisic acid insensitive 5) plays a central role in regulating responses to ABA (Abscisic acid) signals during seed germination and early growth. In Arabidopsis thaliana, ABI5 is strongly induced by ABA, and high ABI5 expression inhibits seed germination. Plant MYB (Myeloblastosis) proteins respond to multiple hormonal signals, including ABA. Moreover, many R2R3 MYB transcription factors show functional similarities to ABI5; however, regulation of ABI5 transcriptional activity by R2R3 MYB factors during seed germination remains insufficiently characterized. In this study, we found that BoMYB96 and BoMYB2 bind the BoABI5 promoter and inhibit its transcription. A. thaliana and Brassica napus lines overexpressing BoMYB96 or BoMYB2 exhibited ABA insensitivity when exposed to exogenous ABA, which increased rapeseed germination rates under ABA treatment. These results demonstrate functional conservation of AtMYB96 and AtMYB2 in ABA signaling and expand understanding of ABI5 transcriptional regulation in the genomes of Brassica oleracea and B. napus.