Integrative tissue-resolved proteomics and metabolomics analysis of oil palm (Elaeis guineensis Jacq.) fruit provides insights into stilbenoid biosynthesis at the interface of primary and secondary metabolism

The oil palm fruit produces highly valuable edible oil from its fleshy mesocarp and seed. Aside from the palm oil and palm kernel oil of economic importance, the non-oil components of the oil palm fruit hold great potential as natural and sustainable products. Most studies focus on the molecular mechanisms regulating the oil palm lipid production and accumulation but little is known about secondary metabolism, specifically stilbenoids in the fruit tissues. This work aims to profile the proteomes and metabolomes of the exocarp, mesocarp, shell and kernel at the ripening stage and to identify the enzymes and metabolites associated with stilbenoid biosynthesis. From a total of 1964 proteins, the mesocarp and exocarp tissues were characterized by high abundance of proteins related to fatty acid, glycolysis and secondary metabolism. Proteins more abundant in the kernel and shell tissues were linked to storage and triacylglycerol synthesis. The enzymes directly involved in stilbenoid biosynthesis are 4-coumarate: coenzyme A ligase (4CL), hydroxycinnamoyl-CoA: shikimate hydroxycinnamoyl transferase (HCT) and trans-resveratrol di-O-methyltransferase (ROMT) which were highly expressed (p < 0.05) in the exocarp, mesocarp and shell tissues but not in the kernel. Trans-resveratrol was detected in the shell and mesocarp from comprehensive metabolome screening, with piceatannol in the shell, exocarp and kernel as well as trans-piceid in the exocarp. The oil palm fruit key proteins reveal tissue-specific cellular functions for primary and secondary metabolism in corroboration with the metabolome profiles, prospective for further quality improvement and optimum utilization of this rich resource.