C/K interactomics in oil palm metabolism and allocation related to yield

Oil palm (Elaeis guineensis Jacq.) is one of the most productive oil crop in the world, with yield values of about 4 t oil ha-1. Potassium (K) is of considerable importance for oil palm production. In fact, K availability is crucial for fruit development by increasing bunch weight and number. Unfortunately, such positive effects of K fertilization remain rather difficult to predict because of the lack of knowledge of underlying metabolic mechanisms. In effect, understanding these mechanisms would allow agronomists to better anticipate oil palm responses in terms of photosynthetic sugar production, respiratory loss, or lipid biosynthesis. The objective of this thesis was precisely to assess the effect of K availability on oil palm metabolic pathways and determine if metabolic changes could be related to oil production. To do so, we conducted our research work in situ, that is, in plantations in Sumatra (Indonesia), using realistic K levels far from excess or deficiency, with two contrasted oil palm crosses (Deli x La Mé and Deli x Yangambi) that are widely used in commercial planting. We combined analysis of functional traits (vegetative biomass, phenology, production and fruit analysis, gas exchanges), elemental analyses, functional genomics (proteomics and metabolomics) in leaflets and fruits during maturation. Furthermore, in order to gain knowledge on the effect of K on the redistribution of photosynthetic products from source to sink organs and show the feasibility of isotopic tracing in the field, a preliminary 13CO2 labelling experiment was carried out. In addition to expected effects of potassium on vegetative traits and bunches (number of fruits and/or total fruit biomass), our results show that K availability affected carbon and nitrogen primary metabolism in both leaflets and developing fruits. In leaves, high K conditions led to an increased photosynthetic capacity reflected by higher content in several enzymes (e.g. sucrose phosphatase) and sugar content (in particular disaccharides), in a cross-dependent manner. In addition, high K reconfigured catabolism, with an increase in respiration, Krebs cycle enzyme content and proteins of the mitochondrial electron transfer chain. In fruits, high K accelerated the kinetics of lipid production (fatty acid synthesis and elongation) and associated pathways, including transitory sugar and transitory starch storage and utilization, amino acid remobilization or activity of the oxidative pentose phosphate cycle. However, final mesocarp lipid composition at maturity appeared to be unchanged by K availability. This thesis presents, for the first time, a detailed metabolic exploration of oil palm in the field and shows that some metabolic traits (metabolites or enzymes) are linked to K availability, thereby opening avenues for the use of leaf biochemical markers to monitor oil palm mineral nutrition.