PHR1-like 7 and phosphatidic acid oppositely regulate TAG degradation and seed oil accumulation in Arabidopsis

Triacylglycerol (TAG) degradation plays an important role in seed oil accumulation, but how this catabolic process is transcriptionally regulated in developing seeds remains poorly understood. Here, we identify a MYB-like helix-turn-helix (HTH) transcriptional regulator, PHR1-like 7 (PHL7), that enhances TAG degradation and decreases seed oil accumulation in Arabidopsis thaliana. PHL7 knockout (KO) plants (phl7) exhibited an approximately 10% increase in seed oil content, whereas PHL7 overexpression (OE) decreased oil content by 8%-13%. Compared with wild-type plants, phl7 displayed reduced expression of TAG degradation genes, including SUGAR-DEPENDENT 1 (SDP1), whereas OE lines exhibited elevated expression. Chromatin immunoprecipitation, electrophoretic mobility shift assays, and transactivation assays demonstrated that PHL7 binds the SDP1 promoter and activates its expression. We further found that PHL7 binds phosphatidic acid (PA), a key intermediate in TAG biosynthesis, and that PA suppresses PHL7 binding to the SDP1 promoter. The lysine residue at position 61 (K61) is required for PA interaction, and introducing the PHL7_K61S mutation into phl7 failed to restore seed oil content to wild-type levels. Together, these findings indicate that PHL7 promotes SDP1 expression, whereas PA attenuates this activity, revealing a lipid-mediated mechanism that balances TAG degradation and seed oil accumulation.