DISSECTING MOLECULAR MECHANISMS TO ENHANCE FRUIT PHOTOSYNTHESIS AND NUTRITIONAL QUALITY IN TOMATO

Fruit development is a highly regulated process involving a series of physiological and biochemical processes. One such critical process is fruit photosynthesis. Prior to ripening, the majority of fruits are green photosynthetic organs. Despite fruits being regarded as photosynthate sinks, fruit photosynthesis contributes to yield and fruit quality as demonstrated in a wide variety of fleshy fruits, pods of legumes/oil seeds, and ears of cereals.Chloroplasts are key organelles in the energy biology of plants that serve as sites of photosynthesis. In addition, chloroplasts also harbor a multitude of interacting metabolic pathways including, biosynthesis of amino acids, fatty acids, vitamins, nucleotides, plant hormones, and a range of specialized metabolites. In a developing fruit, chloroplasts transform into chromoplasts for carotenoid formation. There is a well-defined positive correlation between chloroplast number and chlorophyll content of the developing fruit and the nutritive value of the ripe fruit. Furthermore, gradients in chlorophyll content and chloroplast number are observed in fleshy fruits, with decreasing gradients from the stem end to the base of the fruit as shown in several Solanaceae fruits.Tomato is one of the world's most consumed vegetables with $1.78 billion economic value in the US in 2022 (USDA-NASS). Tomato serves as a great model to study fleshy fruit development, including chloroplast development in fruits. In tomato, fruit photosynthesis contributes up to 20% of the total fruit carbohydrate. Interestingly, some tomato varieties exhibit fruit chlorophyll gradients, and the others do not. Research from our lab and others have identified multiple genes including transcription factors (TFs) that function in chloroplast development and chlorophyll gradient formation in tomato fruit.Overall goal of this research is to dissect the molecular basis of fruit-specific chloroplast development and chlorophyll gradient formation by leveraging the tremendous resources available for tomato, including a diverse collection of sequenced accessions, extensive phenotypic variation in fruit chlorophyll content, and a range of chlorophyll gradient phenotypes. The specific objectives of this proposal are Obj 1: Genome-wide association studies (GWAS) to identify loci underlying fruit chlorophyll content and chlorophyll gradient formation by utilizing a tomato diversity panel, Obj 2: Identify novel structural and regulatory sequences and define a gene regulatory network (GRN) for fruit chloroplast development. This will be achieved by gene expression profiling of fruit from differential chlorophyll accumulating tomato accessions and mutants and integrating with GWAS and further validating the GRN by identifying genome-wide TF binding sites for important TFs. Key deliverables of this project are identification of novel structural and regulatory sequences governing fruit-specific chloroplast development and their functional relationships in a regulatory circuit. This research will facilitate strategies to engineer photosynthesis and tailor chloroplast-derived metabolites to increase productivity and nutrient value of fleshy fruits.