Thiamine biosynthesis in Arabidopsis thaliana assembles the cofactor via convergent thiazole and pyrimidine branches primarily in plastids, producing thiamine monophosphate (TMP) that is transported to cytosol and mitochondria for final activation. The thiazole moiety derives from glycine through THI1, which uses NAD⁺ and its active-site cysteine in a suicide reaction to generate ADP-5-ethyl-4-methylthiazole-2-carboxylate, processed to 4-methyl-5-(2-phosphooxyethyl)thiazole (HET-P); concurrently, the pyrimidine branch taps purine metabolism where THIC rearranges 5-aminoimidazole ribonucleotide (AIR) with SAM to 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate (HMP-P), followed by kinase activation to HMP-PP. TMP synthase (TH1) catalyzes the key condensation of HET-P and HMP-PP to TMP plus pyrophosphate, requiring no further thiazole modification, with TMP then hydrolyzed by phosphatase isoforms (e.g., TH2/TMPPase) to free thiamine; this pathway is validated by pale/viable phenotypes of Arabidopsis thi1, thic, and th1 mutants rescued by thiamine supplementation, reflecting tight plastid-mitochondria coordination. ​

Thiamine biosynthesis References