Cloning And Functional Analysis Of Gene Coding For Phytoene Synthase (PSY) From Gentiana Lutea

Carotenoids are one of most abundant classes of natural compounds, often highly colored with yellow, orange or red, derived from isoprenoids. They are synthesized in all photosynthetic organisms, as well as some bacteria, fungi and algae. They accumulate in the chloroplasts of leaves and in the chromoplasts of many flowers and fruits. Carotenoids have fundamental roles in human nutrition as antioxidants and vitamin A precursors. It has been demonstrated their consumption is increasing associated with protection from a diverse of diseases. Animals and humans are unable to synthesize carotenoids de novo and must depend on dietary carotenoids. Thus they must acquire them from their diet. The first committed step in the plastid-localized carotenoid biosynthetic pathway is mediated by the nuclear-encoded phytoene synthase (PSY). It has been demonstrated PSY is the key enzyme limiting in carotenoid biosynthesis in tomato fruit, canola seeds, potato tubers, Arabidopsis thaliana seeds, Gentiana lutea flower petals and maize endosperm. The sole overexpression of phytoene synthase has a potent effect on carotenoid levels in storage organs generally, e.g. resulting in a 1.9-fold increase in tomato fruits, a 50-fold increase in canola seeds, a 43-fold increase in Arabidopsis seeds and a 8-fold increase in potato tubers.In the present study, the phytoene synthase (PSY) 2 and 3 cDNAs were cloned from flower petal cDNA library of Gentiana lutea. The G. lutea PSY2 (GlPSY2) and PSY3 (GlPSY3) cDNA information were deposited in NCBI (National Center for Biotechnology Information) GenBank (Accession numbers: EF203259 and EF203260, respectively). The full-length of nucleotide sequence of GlPSY2 cDNA consisted of 1923 bp with a 1275 bp open reading frame (ORF), a 497 bp 5' terminal and a 151 bp 3' terminal non-coding regions, respectively. The deduced amino acid sequence of GlPSY2 cDNA was a polypeptide of 424 amino acid residues with molecular weight of 48298.65 D. The full-length of nucleotide sequence of GlPSY3 cDNA was 1765 bp with a 1278 bp open reading frame (ORF), 399 bp 5' terminal and 88 bp 3' terminal non-coding regions, respectively. The deduced amino acid sequence of GlPSY3 cDNA was a polypeptide of 424 amino acid residues with molecular weight of 48399.75 D. The isoelectric point of both of GlPSY2 and GlPSY3 was 8.79. The GlPSY2 and GlPSY3 amino acid sequences have higher identities with known functional PSY sequences from higher plants. The indicated function of G. lutea PSY2 and PSY3 cDNAs was estabilished by heterologous complementation in engineering Escherichia coli.