A tree peony TCP transcription factor, PrTCP4, acts as a negative regulator of seed oil accumulation

Seed oils are essential dietary sources of fatty acids (FAs) and serve as important feedstocks for industrial and bioenergy applications. However, the transcriptional networks governing their accumulation in plant seeds remain largely elusive. We previously identified an INDETERMINATE DOMAIN (IDD) transcription factor, PrIDD7, as a negative regulator of oil deposition in tree peony. Here, our work reveals TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR4 (PrTCP4), a nucleus‑localized TCP family TF that physically interacts with PrIDD7. Transient overexpression of PrTCP4 in tobacco leaves and stable overexpression in Arabidopsis seeds significantly reduced oil content. In contrast, silencing of endogenous PrTCP4 in tree peony seeds increased oil accumulation and was accompanied by increased expression of multiple genes governing FA biosynthesis and triacylglycerol assembly. Further transcriptional regulation assays demonstrated that PrTCP4 repressed transcription of PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE , a key acyltransferase gene, and that interaction with PrIDD7 significantly potentiated this repressive activity. Our findings uncover PrTCP4 as a novel suppressor of seed oil accumulation and demonstrate the synergistic reinforcement of PrTCP4‑mediated repression by PrIDD7, thereby advancing our understanding of oil accumulation regulatory networks and providing a valuable target gene for improving oilseed crops.