Differential induction of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase genes in Arabidopsis thaliana by wounding and pathogenic attack.

We have isolated cDNAs from two distinct genes encoding 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15) in Arabidopsis thaliana. Predicted protein sequences from both genes, DHS1 and DHS2, and a potato DAHP synthase gene are highly related, but none shows significant sequence similarity to conserved microbial DAHP synthase proteins. Despite this structural difference, the DHS1 cDNA complements mutations in a yeast strain lacking DAHP synthase activity. DHS1 RNA levels increase in Arabidopsis leaves subjected either to physical wounding or to infiltration with pathogenic Pseudomonas syringae strains. DHS2 RNA levels are not increased by these treatments, suggesting that the DHS1 and DHS2 proteins fulfill different physiological functions. Other enzymes in the Arabidopsis aromatic pathway are also encoded by duplicated genes, an arrangement that may allow independent regulation of aromatic amino acid biosynthesis by distinct physiological requirements such as protein synthesis and secondary metabolism. The presence of amino-terminal extensions characteristic of chloroplast transit peptides on DHS1 and DHS2 suggests that both proteins may be targeted to the chloroplast.