Nucleotide sequence of acyl-acyl carrier protein: glycerol-3-phosphate acyltransferase from cucumber.

Acyl-acyl carrier protein-G3PAT2 carries out the first step of lipid biosynthesis in the plastid pathway. Fatty acids, primarily C18:1 and C16:0, produced by the chloroplastlocalized fatty acid synthase, are esterified by G3PAT to the sn-1 position of glycerol-3-phosphate, producing lysophosphatidic acid. A cDNA clone from squash and cDNA and genomic clones from Arabidopsis thaliana encoding G3PAT have been isolated previously (2, 8). In this paper, we present the sequence of this gene from cucumber (Fig. 1; Table I). This gene was isolated as part of a study to determine why plants differ in the ability to tolerate cold, nonfreezing, temperatures. Several studies have demonstrated a correlation between chilling sensitivity and the proportion ofPG containing only saturated or trans-unsaturated C16 acyl groups (disaturated PG) (4-6). The amount of disaturated PG depends at least in part on the specificity of the G3PAT. It has been suggested that G3PAT from chilling-sensitive plants utilize C16:0, C18:0, or C18: 1 as substrates, whereas the enzyme from chilling-resistant plants discriminates against C16:0 (1). The PCR was used with cucumber genomic DNA and oligonucleotide primers based on the squash nucleotide sequence to produce a 1 kilobase pair DNA fragment that was used to probe a cucumber cDNA library. Of three clones isolated, one cDNA was truncated at the 5' end and another was truncated at both ends. The DNA sequence ofboth cDNA clones was identical in the region of overlap. The third clone appears to be genomic in origin. This conclusion is based on the presence of introns, the absence of a polyadenylation