Expression of a phytoene synthase gene and characteristic carotenoid accumulation during citrus fruit development

A cDNA clone encoding a protein homologue to phytoene synthase (PSY, CitPSY 1) was isolated from Satsuma mandarin (Citrus unshiu Marc,) fruit. Expressi on analysis revealed the presence of the CitPSY1 transcript in flowers and leaves, with a higher level detected in the mature than in the young leaves . In fruit, the transcript was present in a low quantity in the flavedo (pe el) and juice sacs/segment epidermis (edible part) at an early developmenta l stage. Later, it began to accumulate towards fruit maturation in both par ts. These fluctuations were in accordance with carotenoid accumulation and chlorophyll disappearance. We suggest that CitPSY1 plays an important role in carotenoid accumulation. We also propose a possible pathway in carotenoi d biosynthesis that is based on the fluctuation of the characteristic carot enoid composition during Satsuma mandarin development.