Differential Regulation of Phytoene Synthase PSY1 During Fruit Carotenogenesis in Cultivated and Wild Tomato Species ( section Lycopersicon).

In plants, carotenoids define fruit pigmentation and are involved in the processes of photo-oxidative stress defense and phytohormone production; a key enzyme responsible for carotene synthesis in fruit is phytoene synthase 1 (PSY1). Tomatoes ( section Lycopersicon) comprise cultivated () as well as wild species with different fruit color and are a good model to study carotenogenesis in fleshy fruit. In this study, we identified homologous genes in five section Lycopersicon species, including domesticated red-fruited and wild yellow-fruited and green-fruited , and . PSY1 homologs had a highly conserved structure, including key motifs in the active and catalytic sites, suggesting that PSY1 enzymatic function is similar in green-fruited wild tomato species and preserved in red-fruited . mRNA expression directly correlated with carotenoid content in ripe fruit of the analyzed tomato species, indicating differential transcriptional regulation. Analysis of the promoter and 5'-UTR sequence revealed over 30 regulatory elements involved in response to light, abiotic stresses, plant hormones, and parasites, suggesting that the regulation of expression may affect the processes of fruit senescence, seed maturation and dormancy, and pathogen resistance. The revealed differences between green-fruited and red-fruited species in the structure of the promoter/5'-UTR, such as the acquisition of ethylene-responsive element by , could reflect the effects of domestication on the transcriptional mechanisms regulating expression, including induction of carotenogenesis during fruit ripening, which would contribute to red coloration in mature fruit.