EgbHLH63 negatively regulates palm fruit oil accumulation by repressing EgDGAT1 transcription

Abstract

Diacylglycerol acyltransferase (DGAT) is a crucial enzyme involved in triacylglycerol (TAG) accumulation. To investigate the regulation of DGAT genes in the mesocarp of oil palm, a key transcription factor, EgbHLH63, was identified by a yeast one-hybrid assay. The interaction between EgbHLH63 and the EgDGAT1 promoter (proEgDGAT1) and its potential role in TAG synthesis were investigated. Binding of EgbHLH63 to proEgDGAT1 was confirmed by dual-luciferase reporter gene assays and EMSA in vitro. Overexpression of EgbHLH63 in oil palm protoplasts resulted in a significant reduction in EgDGAT1 expression. Silence of EgbHLH63 in transgenic embryoids restored high levels of EgDGAT1 expression and significantly increased TAG content. In addition, two other transcription factors, EgULT1 and EgZFP, were identified as interacting with EgbHLH63. They recognized B-box and AT-rich motifs in the EgDGAT1 promoter, respectively. These two transcription factors also negatively regulated EgDGAT1 expression, thereby affecting oil accumulation. Collectively, the results shed light on the lipid mechanism pathway involving EgDGAT1 in the mesocarp and offer promising research avenues for improving oil yield and quality in oil palm.