EgSnRK2-EgARF18-EgFAD2 regulatory axis fine-tunes unsaturated fatty acid metabolism in oil palm (Elaeis guineensis)

Palm oil, extracted from the mesocarp of Elaeis guineensis, features a balanced ratio of saturated to unsaturated fatty acids (UFAs) and a high oleic acid (C18:1) content (∼40 %) of its total fatty acids. The primary UFAs, C18:1 and linoleic acid (C18:2), are regulated by EgFAD2, a key enzyme in UFA biosynthesis. To explore the regulatory mechanisms, we used yeast one-hybrid screening to identify transcription factors interacting with the EgFAD2 promoter (proEgFAD2), revealing EgARF18, an auxin response factor, as a direct binder. This interaction was validated through overexpression and virus-induced gene silencing (VIGS) in oil palm protoplasts and embryogenic calli. Protein interaction assays (yeast two-hybrid, GST-pulldown, and BiFC) confirmed that EgARF18 physically interacts with EgSnRK2, a serine/threonine kinase. Overexpression of EgSnRK2 in embryoids downregulated EgARF18 and EgFAD2, increasing C18:1 (from 22.4 % to 26.9 %) while reducing C18:2 (from 27.1 % to 21.2 %) levels. These results establish a negative regulatory pathway where EgSnRK2 modulates the EgARF18-EgFAD2 axis to fine-tune UFA metabolism. This study provides molecular insights into fatty acid desaturation in oil palm, offering targets for precision breeding to develop tailored palm oil varieties with optimized C18:1 or C18:2 content for industrial and nutritional applications.