Involved in maintaining the supply of chorismate for the biosynthesis of the aromatic amino acids and other chorismate-derived metabolites. D-erythrose 4-phosphate + H2O + phosphoenolpyruvate = 7-phospho-2-dehydro-3-deoxy-D-arabino-heptonate + phosphate Metabolic intermediate biosynthesis; chorismate biosynthesis; chorismate from D-erythrose 4-phosphate and phosphoenolpyruvate: step 1/7. Highest levels seen in the roots and lower levels seen in the stems and flowers. Is undetectable in the leaves and cotyledons. Belongs to the class-II DAHP synthase family.