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, CitPSY1) was isolated from Satsuma mandarin (Citrus unshiu Marc,) fruit. Expression 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 (peel) and juice sacs/segment epidermis (edible part) at an early developmental stage. Later, it began to accumulate towards fruit maturation in both parts. 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 carotenoid biosynthesis that is based on the fluctuation of the characteristic carotenoid composition during Satsuma mandarin development.