Gibberellin signaling protein PoGID2 cooperates with PoFUS3 to enhance oil and α-linolenic acid accumulation in Paeonia ostii seeds

Paeonia ostii seeds are characterized by exceptionally high α-linolenic acid (ALA, C18:3) content, yet the molecular connection between ALA accumulation and gibberellin (GA) signaling remains poorly elucidated. In this study, the GA signaling component PoGID2 was differentially expressed during seed oil accumulation: its transcript level increased 3.48‑fold during the oil accumulation period (20–80 days after pollination, DAP) and was positively correlated with the amount of seed oil accumulated in this period, suggesting that PoGID2 may participate in the regulation of seed oil biosynthesis. Functional assays in Nicotiana benthamiana and detached embryos/seeds of P. ostii , together with GC-MS and RT-qPCR analyses, showed that PoGID2 promotes total fatty acids (FAs) accumulation and shifts FA composition toward unsaturated species. In particular, PoGID2 enhanced the expression of PoFAD2 , PoFAD3 , PoFAD8 , and PoDGAT1 , thereby favoring ALA accumulation. Moreover, PoGID2 directly interacts with the transcription factor PoFUS3 and the two proteins act synergistically. Co‑expression of PoGID2 and PoFUS3 enhanced lipid accumulation to a greater extent than expression of PoGID2 alone: PoGID2 expression alone increased total FAs and ALA levels by approximately 1.26‑fold and 1.29‑fold, respectively, relative to the control; co‑expression with PoFUS3 produced further increases of approximately 1.10‑fold and 1.19‑fold, respectively, relative to the PoGID2‑only group, indicating a pronounced synergistic effect. These findings indicate that PoGID2 functions as a regulatory node linking GA signaling to seed oil biosynthesis and provide a new target for improving ALA-rich woody oil crops.