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

Abstract

to accumulate towards fruit maturation in both parts. These A cDNA clone encoding a protein homologue to phytoene synthase (PSY, CitPSY1) was isolated from Satsuma man-fluctuations were in accordance with carotenoid accumulation and chlorophyll disappearance. We suggest that CitPSY1 darin (Citrus unshiu Marc.) fruit. Expression analysis revealed the presence of the CitPSY1 transcript in flowers and plays an important role in carotenoid accumulation. We also leaves, with a higher level detected in the mature than in the propose a possible pathway in carotenoid biosynthesis that is based on the fluctuation of the characteristic carotenoid com-young leaves. In fruit, the transcript was present in a low position during Satsuma mandarin development. quantity in the flavedo (peel) and juice sacs/segment epidermis (edible part) at an early developmental stage. Later, it began (C 40 ) via the intermediate prephytoene pyrophosphate (PPPP) (Cunningham and Gantt 1998). Subsequently, the colorless compound phytoene is converted into yellow (n-carotene), orange (neurosporene) and red (lycopene) carotenoids by 4 sequential desaturations of phytoene by introducing the conjugated double bonds Scolnik 1995, Cunningham andGantt 1998). In plants and algae, these steps are catalyzed by two enzymes, phytoene desaturase (PDS) and n-carotene desaturase (ZDS). Cyclization reaction by i or m cyclase converts lycopene to ior l-carotene, respectively (Cunningham et al. 1996). When combined, i or m cyclases convert lycopene to hcarotene (Cunningham et al. 1996). The desaturation and cyclization reactions occur within plastids and are catalyzed by integral membrane enzymes (Bramley 1985). Details of genes and enzymes for carotenoid biosynthesis in plants have been recently reviewed by Cunningham and Gantt (1998).

cDNA cloning of the phytoene synthase (PSY) and expression analysis of PSY and carotenoid cleavage dioxygenase genes in Osmanthus fragrans

“…The contribution of transcript abundance of PSY gene to the carotenoid accumulation was studied in many plant species, including Solanum lycopersicum (Giuliano et al 1993), Capsicum annuum (Bouvier et al 1994) and Citrus unshiu (Ikoma et al 2001;Kato et al 2004). A pieces of evidence clearly demonstrated importance of PSY in controlling carotenoid biosynthesis in developing flowers and ripening fruit, in which these organs, an increase in PSY transcript levels to enhance carotenoid production (Giuliano et al 1993;Moehs et al 2001;Zhu et al 2002;Bramley 2002).…”

Structure and Expression Levels of Alleles of Citrus Zeaxanthin Epoxidase Genes

“…Carotenoid content and composition in Citrus fruit varies greatly among varieties, and depends on growing conditions (Gross, 1987;Ikoma et al, 2001;Kato et al, 2004). Satsuma mandarin (Citrus unshiu Marc.)…”

Mechanism of Carotenoid Accumulation in Citrus Fruit

“…Satsuma mandarin accumulated β-cryptoxanthin as a major carotenoid in mature fruit, whereas Valencia orange mainly accumulated violaxanthin isomers (Fig. 4A, B) (Goodner et al, 2001;Ikoma et al, 2001;Lee and Castle, 2001;Molnár and Szabolcs, 1980). The ratios of β-cryptoxanthin/ violaxanthin in juice sacs were 5.17 in Satsuma mandarin and 0.10 in Valencia orange.…”

“…Mandarin varieties, such as Satsuma mandarin (Citrus unshiu Marc. ), accumulated β-cryptoxanthin predominantly in the flavedo as well as juice sacs in mature fruit (Goodner et al, 2001;Ikoma et al, 2001). In contrast, mature sweet orange (Citrus sinensis Osbeck) accumulated violaxanthin isomers predominantly in fruit (Lee and Castle, 2001;Molnár and Szabolcs, 1980), in which 9-cis-violaxanthin was found to be the principal carotenoid (Molnár and Szabolcs, 1980).…”