Catalyzes the first two consecutive steps of tetrahydrofolate biosynthesis (PubMed:17289662). Plays a role in seed stress response and survival (PubMed:17289662, PubMed:21996493). 6-hydroxymethyl-7,8-dihydropterin + ATP = (7,8-dihydropterin-6-yl)methyl diphosphate + AMP + H(+) (7,8-dihydropterin-6-yl)methyl diphosphate + 4-aminobenzoate = 7,8-dihydropteroate + diphosphate Inhibited by sulfanilamide. Cofactor biosynthesis; tetrahydrofolate biosynthesis; 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine diphosphate from 7,8-dihydroneopterin triphosphate: step 4/4. Cofactor biosynthesis; tetrahydrofolate biosynthesis; 7,8-dihydrofolate from 2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine diphosphate and 4-aminobenzoate: step 1/2. Expressed exclusively in reproductive tissues. Expressed in early stages of seed development, until the late globular stage of embryo. Not detected at the heart stage of embryo development. Up-regulated by slat stress (PubMed:17289662). Up-regulated by oxidative stress (PubMed:21996493). No visible phenotype (PubMed:17289662). Increased sensitivity to oxidative stress (PubMed:21996493). In the N-terminal section; belongs to the HPPK family. In the C-terminal section; belongs to the DHPS family. Translation N-terminally extended. Translation N-terminally extended.