Sequence of a cDNA Clone Encoding a Potato (Solanum tuberosum) Tuber Lipoxygenase

LOX (EC 1.13.11.12) are ubiquitous plant enzymes that catalyze the hydroperoxidation of polyunsaturated fatty acids; potato tubers contain high levels of LOX (Pinsky et al., 1971). LOX are believed to catalyze a key step in the formation of jasmonates, which have profound effects on plant physiology and gene expression (Staswick, 1992), including the induction of tuber formation in potatoes (Koda et al., 1991). LOX have also been implicated in the arachidonic acid-elicited hypersensitive cell death response of potato discs and callus lines (Bostock et al., 1992; Vaughn and Lulai, 1992). The potato tuber LOX that has been purified effects hydroperoxidation predominantly at the 5-carbon of arachidonic acid (Shimizu et al., 1990) and thus differs in positional specificity from the well-characterized soybean seed arachidonate 15-LOX (Boyington et al., 1993); analysis of its structure may afford clues to the basis of positional specificity of hydroperoxidation by plant LOX. This report describes loxl:St:Z, a Solanum tuberosum LOX cDNA that corresponds to mRNA that is abundant in developing tubers. The sequence, described in Table I, includes 200 bp between the stop codon and the poly(A) tail, and 1 bp 5' to the initiation codon. The proposed initiating ATG aligns well with other, homologous plant LOX sequences; primer extension using an oligonucleotide corresponding to nucleotides 2 to 22 indicates that the potato tuber LOX mRNA has 74 nucleotides of 5' noncoding sequence. The amino acid sequence predicted by 10x2: St:2 is more similar to the Arubidopsis thuliunu LOX 1 sequence reported by Melan et al. (1994) than to any other published LOX sequence, showing 80% similarity (66% identity) to Arubidopsis LOX 1. Boyington et al. (1993) described an interna1 cavity (11) in soybean 15-LOX that is likely to accommodate the fatty acid substrate. Within this cavity they described 14 highly conserved amino acids; these are also conserved in the sequence predicted from 1oxl:St:Z. One residue (Phe557) in the cavity may be involved in the determination of positional specificity (see