REGULATION OF CAROTENOID BIOSYNTHESIS DURING TOMATO DEVELOPMENT

Phytoene synthase (Psy) and phytoene desaturase (Pds) are the first de dicated enzymes of the plant carotenoid biosynthesis pathway. We repor t here the organ-specific and temporal expression of PDS and PSY in to mato plants. Light increases the carotenoid content of seedlings but h as little effect on PDS and PSY expression. Expression of both genes i s induced in seedlings of the phytoene-accumulating mutant ghost and i n wild-type seedlings treated with the Pds inhibitor norflurazon. Root s, which contain the lowest levels of carotenoids in the plant, have a lso the lowest levels of PDS and PSY expression. In flowers, expressio n of both genes and carotenoid content are higher in petals and anther s than in sepals and carpels. During flower development, expression of both PDS and PSY increases more than 10-fold immediately before anthe sis. During fruit development, PSY expression increases more than 20-f old, but PDS expression increases less than threefold. We concluded th at PSY and PDS are differentially regulated by stress and developmenta l mechanisms that control carotenoid biosynthesis in leaves, flowers, and fruits. We also report that PDS maps to chromosome 3, and thus it does not correspond to the GHOST locus, which maps to chromosome 11.