Diurnal biomarkers reveal key photosynthetic genes associated with increased oil palm yield

by Bee Keat Neoh, Yick Ching Wong, Huey Fang Teh, Theresa Lee Mei Ng, Soon Huat Tiong, Tony Eng Keong Ooi, Mohd. Zairey Md. Zain, Mohd. Amiron Ersad, Chee Keng Teh, Heng Leng Lee, Siti Khadijah Mohd Rais, See Siang Cheah, Fook Tim Chew, Harikrishna Kulaveerasingam, David Ross Appleton

To investigate limiters of photosynthate assimilation in the carbon-source limited crop, oil palm (Elaeis guineensis Jacq.), we measured differential metabolite, gene expression and the gas exchange in leaves in an open field for palms with distinct mesocarp oil content. We observed higher concentrations of glucose 1-phosphate, glucose 6-phosphate, sucrose 6-phosphate, and sucrose in high-oil content palms with the greatest difference being at 11:00 (p-value ≤0.05) immediately after the period of low morning light intensity. Three important photosynthetic genes were identified using differentially expressed gene analysis (DEGs) and were found to be significantly enriched through Gene Ontology (GO) and pathway enrichment: chlorophyll a-b binding protein (CAB-13), photosystem I (PSI), and Ferredoxin-NADP reductase (FNR), particularly for sampling points at non-peak light (11:00 and 19:00), ranging from 3.3-fold (PSI) and 5.6-fold (FNR) to 10.3-fold (CAB-13). Subsequent gas exchange measurements further supported increased carbon assimilation through higher level of internal CO₂ concentration (Ci), stomatal conductance (g_s) and transpiration rate (E) in high-oil content palms. The selection for higher expression of key photosynthesis genes together with CO₂ assimilation under low light is likely to be important for crop improvement, in particular at full maturity and under high density planting regimes where light competition exists between palms.