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Zhang, J, Tao, N, Xu, Q, Zhou, W, Cao, H, Xu, J and Deng, X (2009) Functional characterization of Citrus PSY gene in Hongkong kumquat (Fortunella hindsii Swingle). Plant Cell Rep. 28:1737-46
Citrus, rich in carotenoids, is the most important fruit crop based on the total annual production. In the carotenoid biosynthesis pathway, phytoene synthase (PSY, EC 188.8.131.52) catalyzes the dimerization of two molecules of geranylgeranyl pyrophosphate (GGPP) to phytoene and has been shown to be a rate-limiting enzyme for the synthesis of carotenoids. In this study, we investigated catalytic activity of CsPSY from Cara Cara navel orange (Citrus sinensis Osbeck) by heterologous expression in Escherichia coli containing a GGPP-producing plasmid. Moreover, the effects of CsPSY overexpression on carotenoid accumulation were also functionally analyzed in transgenic Hongkong kumquat (Fortunella hindsii Swingle). The resulting transgenic plants produced orange fruits, and extracts from the fruits of four overexpressing plants had a 2.5-fold average increase of phytoene with the content approximately 71.38 microg/g fresh weight. Lycopene, beta-carotene, and beta-cryptoxanthin in transgenic fruits were also markedly increased, whereas the levels of lutein and violaxanthin kept nearly unchanged with 1.1-1.3 folds variation. Transcript levels of carotenoid biosynthetic genes in the CsPSY overexpressed plants remained unaltered except that PDS and ZDS showed a minor increase. This study suggests that CsPSY plays a crucial role in citrus carotenoid biosynthesis and could be used as a means of engineering fruit crop for the production of carotenoids.
Alkyl and Aryl Transferases/chemistry; Alkyl and Aryl Transferases/genetics; Alkyl and Aryl Transferases/metabolism; Amino Acid Sequence; Carotenoids/biosynthesis; Citrus/enzymology; Citrus/genetics; Citrus/growth & development; DNA, Complementary; Gene Expression Regulation, Plant; Molecular Sequence Data; Phylogeny; Plants, Genetically Modified
|Gene product||Qualifier||GO Term||Evidence Code||with/from||Aspect||Extension||Notes||Status|
|GO:0046905: phytoene synthase activity||
Figure 3(a),(b),(c):HPLC analysis revealed that the GGPP-accumulating E. coli cells transformed with the CsPSY construct showed a peak (Fig. 3b, peak 1) that was not detected in the empty vector control, pACCRT-E/pET-28a (Fig. 3a). The retention time and absorption spectrum of the peak 1 matched well with those of the peak 2 presented in the positive control carrying pACCRT-EB for phytoene biosynthesis (Fig. 3c, peak 2).
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