Involved in biosynthesis of the thiamine precursor thiazole. Catalyzes the conversion of NAD and glycine to adenosine diphosphate 5-(2-hydroxyethyl)-4-methylthiazole-2-carboxylic acid (ADT), an adenylated thiazole intermediate. The reaction includes an iron-dependent sulfide transfer from a conserved cysteine residue of the protein to a thiazole intermediate. The enzyme can only undergo a single turnover, which suggests it is a suicide enzyme. May have additional roles in adaptation to various stress conditions and in DNA damage tolerance. Acts as a positive regulator for the abscisic acid-induced activation of slow type anion channels during stomatal closure by repressing CPK33 kinase activity. [ADP-thiazole synthase]-L-cysteine + glycine + NAD(+) = [ADP-thiazole synthase]-dehydroalanine + ADP-5-ethyl-4-methylthiazole-2-carboxylate + 2 H(+) + 3 H2O + nicotinamide Binds 1 Fe cation per subunit. Homooctomer (PubMed:16912043, PubMed:24637331). Interacts with RBCX1 and RBCX1 (PubMed:21922322). Interacts with CPK33 (PubMed:26662273). Expressed at high levels in chloroplast-containing parenchymatic cells of leaves, inflorescence shoots and flowers, and at lower levels in the vascular system (PubMed:8771789). In young plants, detected in roots and shoots including cotyledons, leaves and hypocotyls (PubMed:12941878). Also observed in apical meristematic regions, siliques and embryos (PubMed:15897230). Low expression in roots, limited to the vascular tissue (PubMed:15897230). Broadly expressed in roots, cotyledons, leaves, hypocotyls, inflorescences, siliques, and strongly in guard cells (PubMed:26662273). Expressed throughout develpoment. Up-regulated by osmotic stress, sugar deprivation, high salinity, and hypoxia (PubMed:15897230, PubMed:22214485). Up-regulated by abscisic acid treatment and drought stress (PubMed:22214485, PubMed:26662273). No effect of thiamine, salicylic acid or paraquat treatments (PubMed:12941878, PubMed:22214485). Down-regulated by dark incubation (PubMed:12941878). During the catalytic reaction, a sulfide is transferred from Cys-216 to a reaction intermediate, generating a dehydroalanine residue (PubMed:22031445, PubMed:24637331). Not phosphorylated in vitro by CPK33 (PubMed:26662273). Mitochondrial precursor. Contains a mitochondrial presequence-like structure at its N-terminus. Belongs to the THI4 family.