Brassica napus BnaC9.DEWAX1 Negatively Regulates Wax Biosynthesis via Transcriptional Suppression of BnCER1-2

Very-long-chain alkane plays an important role as an aliphatic barrier. We previously reported that BnCER1-2 was responsible for alkane biosynthesis in Brassica napus and improved plant tolerance to drought. However, how the expression of BnCER1-2 is regulated is still unknown. Through yeast one-hybrid screening, we identified a transcriptional regulator of BnCER1-2, BnaC9.DEWAX1, which encodes AP2\ERF transcription factor. BnaC9.DEWAX1 targets the nucleus and displays transcriptional repression activity. Electrophoretic mobility shift and transient transcriptional assays suggested that BnaC9.DEWAX1 repressed the transcription of BnCER1-2 by directly interacting with its promoter. BnaC9.DEWAX1 was expressed predominantly in leaves and siliques, which was similar to the expression pattern of BnCER1-2. Hormone and major abiotic stresses such as drought and high salinity affected the expression of BnaC9.DEWAX1. Ectopic expression of BnaC9.DEWAX1 in Arabidopsis plants down-regulated CER1 transcription levels and resulted in a reduction in alkanes and total wax loads in leaves and stems when compared with the wild type, whereas the wax depositions in the dewax mutant returned to the wild type level after complementation of BnaC9.DEWAX1 in the mutant. Moreover, both altered cuticular wax composition and structure contribute to increased epidermal permeability in BnaC9.DEWAX1 overexpression lines. Collectively, these results support the notion that BnaC9.DEWAX1 negatively regulates wax biosynthesis by binding directly to the BnCER1-2 promoter, which provides insights into the regulatory mechanism of wax biosynthesis in B. napus.