bHLH7-PDF2 module-mediated transcriptional regulation controls seed oil accumulation in Arabidopsis thaliana

Seed oil accumulation is the precise coordination of multiple factors, of which transcription factors (TFs) play crucial roles in governing this process. However, the identification of TFs, especially the information on how the crosstalk between different TF families orchestrates the transcriptional network associated with seed oil accumulation remains still largely unknown. Here, we reported that a basic helix-loop-helix TF bHLH7 is highly expressed in the developing embryo and negatively controls seed oil accumulation by directly suppressing the expression of six key genes involved in fatty acid biosynthesis. Molecular and genetic analysis revealed that bHLH7 physically interacts with a homeodomain-leucine zipper TF, PROTODERMAL FACTOR2 (PDF2), which is also proven to act as a negative modulator of seed oil accumulation. We demonstrated that PDF2 shares three common targets with bHLH7 and enhances the transcriptional repression activity of bHLH7 to these target genes. Further studies indicated that PDF2 is epistatic to bHLH7 in regulating seed oil accumulation. Additionally, genetic evidence showed that PYRUVATE DEHYDROGENASE E1 BETA1 is required for bHLH7-PDF2 module-mediated seed oil accumulation. Collectively, we reveal a genetic and molecular framework by which the bHLH7-PDF2 module controls seed oil accumulation in A. thaliana, and provide promising targets for genetic manipulation of oil-producing crops to improve seed oil quantity and quality.