Cloning and Sequencing of a Second cDNA Encoding 3-Deoxy-d-arabino-Heptulosonate 7-Phosphate Synthase from Solanum tuberosum L.

DAHP2 synthase (EC 4.1.2.15) is the first enzyme of the shikimate pathway that leads to the biosynthesis of the aromatic amino acids and derived secondary metabolites. The enzyme is induced by glyphosate (6), wounding (1, 4), and fungal elicitor (4, 5). Previously, a cDNA encoding DAHP synthase, which we call shkA, was cloned and sequenced from potato cells grown in suspension culture (2); that cDNA was used to obtain the homolog from tobacco cells (7) and two sequences from Arabidopsis thaliana (4). We report here the sequence of shkB, a second cDNA encoding potato DAHP synthase (Table I, Fig. 1). The shkB cDNA was cloned using the polymerase chain reaction (3) and degenerate primers based on amino acid sequences of DAHP synthase purified from potato tuber. The 2014-bp shkB sequence contains an open reading frame of 511 codons that is 30 codons shorter than the one of shkA. The deduced amino acid sequences of the shkA and shkB products share 78% identity; however, identity in the Nterminal 60 residues is only 42%, and residues 63 to 85 of the shkA product are missing in the shkB product. The amino acid sequence of the shkB product is 80% identical with the homolog from tobacco (7). A. thaliana has two genes encoding DAHP synthase (4); the corresponding cDNAs are homologous to shkA and shkB.