Tomato is one of the most economically relevant crops in the world and is the main model system for fruit ripening studies at biochemical, genetic and molecular levels. In this climacteric fruit, a sudden increase in respiration takes place at the onset of ripening, usually in concert with increased production of ethylene that eventually impacts fruit color, firmness, taste, and flavor. During ripening, tomato accumulates high contents of health-promoting carotenoids (pro-vitamin A, antioxidants), which require a high production of carbon precursors and ATP. In this respect, both mitochondrial and chromoplast respiration have been proposed to play important roles in fruit ripening and carotenoid metabolism. The general aim of this project is to determine the contribution of mitochondrial respiration to the supply of energy and carbon for the production of carotenoids in tomato fruit during ripening. In particular, we will perform metabolomics of genetically modified tomatoes with altered mitochondrial and chromoplast respiration at different ripening stages. Furthermore, 13C- and 14C-labelling experiments will be performed to trace the fate of carbon from primary to secondary metabolites. In parallel, we will measure the relative glycolytic and TCA cycle fluxes and, for the first time in tomato, the in vivo activities of mitochondrial electron transport chain pathways by using the 18O fractionation technique. Combining these data with the analysis of transcript and protein levels of the main components of respiratory and carotenoid pathways and mathematical modelling will unveil novel metabolic checkpoints and connections between primary and secondary metabolism during fruit ripening. The generated new insights should contribute to the implementation of new biotechnological approaches to produce fruits with enhanced levels of carotenoids and other health-promoting secondary metabolites.
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