Phytoene Desaturase from Arabidopsis

Carotenoids are isoprenyl pigments necessary for protection of the photosynthetic apparatus in a11 green plants. One of the intermediate steps in carotenoid biosynthesis is the conversion of phytoene to {-carotene via two dehydrogenation reactions catalyzed by the enzyme PDS. We have previously cloned cDNAs for this enzyme from soybean (Glycine max; Bartley et al., 1991) and tomato (Lycopersicon esculentum; G.E. Bartley and P.A. Scolnik, unpublished data; GenBank accession number M88683). To study carotenoid biosynthesis in Arabidopsis thaliana, we have isolated a PDS cDNA from this organism. This report describes the subcloning and sequencing of this cDNA, which was isolated by screening a XZAP cDNA library using a random-primed 32P-labeled PDS cDNA from tomato. Three positive plaques were isolated, purified, and excised and the resulting inserts in plasmids were identified by sequencing with a primer previously used to sequence the tomato PDS cDNA. These inserts proved to be identical except for small differences in length, which may be due to exonuclease activity, since no poly(A) tails were found. The sequence contains a good consensus translation start site at the 5’ end of the open reading frame (Liitke et al., 1987). The single open reading frame encodes a protein of 566 amino acids with a putative transit peptide and a nucleotide binding site motif in the N-terminal region of the mature peptide (Bartley et al., 1991). Comparison of the deduced mature peptide sequence to the soybean mature PDS sequence showed 80% identity at the nucleotide level and 88.5% identity and 92.7% similarity at the amino acid level. Additionally, there is significant homology of the putative transit peptide amino acid sequence to the soybean, tomato, and Dunaliella bardowil transit peptide sequences (Pecker et al., 1992).