Mediator subunit MED25 represses ABI5-dependent activation of erucic acid biosynthetic gene FAE1 in Brassica napus

ABSCISIC ACID INSENSITIVE 5 (ABI5) is a key regulator that represses seed germination, flowering, and seedling growth in Arabidopsis thaliana and functions in abscisic acid (ABA) signal transduction. However, whether ABI5 is involved in other biological processes and its interacting partners remain largely unknown. Here, we show that BnaABI5 , an ortholog of AtABI5 , positively regulates erucic acid synthesis and the transcript level of the marker gene FAE1 in Brassica napus . Expression patterns of BnaABI5 and BnaFAE1 overlap during specific stages of seed development, as indicated by the BnIR database, and GUS staining assays show that both genes are expressed in seeds. BnaABI5 is a bZIP transcription factor that localizes to the nucleus and activates transcription of the reporter gene LacZ . We further demonstrate that the mediator subunit BnaMED25 is involved in modulating erucic acid synthesis through interaction with BnaABI5 in vivo and in vitro . Dual-luciferase assays and electrophoretic mobility shift assays (EMSAs) indicate that BnaMED25 facilitates BnaABI5-mediated regulation of BnaFAE1 expression. Genetic experiments indicate that, compared with wild-type Col-0 and the variety “Wangxiangyou1881”, the transcript level of the marker gene FAE1 is increased in BnaABI5 -overexpressing Arabidopsis and oilseed rape, respectively. Erucic acid content in the tested seeds exhibited a corresponding trend. Taken together, these results demonstrate that BnaMED25 is involved in BnaABI5-mediated regulation of erucic acid accumulation and reveal a mechanism by which ABI5 and its recruiting factor play a significant role in long-chain fatty acid synthesis.