Vitamin B1 (Thiamine)

Abstract Thiamine (vitamin B 1 ) is essential for human metabolism and is particularly important for proper brain functioning. Plants, which are the best source of this vitamin for human nutrition, synthesize thiamine in three stages. The first of these involves the independent formation of thiazole and pyrimidine moieties. In the next phase, these are coupled together to form thiamine monophosphate. The final step results in the formation of the active form of vitamin B 1 , thiamine diphosphate, which functions as a major enzymatic cofactor. The biosynthesis of thiamine is regulated through feedback inhibition by the end product of the pathway, that is, thiamine diphosphate. This regulatory mechanism involves the binding of thiamine diphosphate by mRNA elements, riboswitches (THI-BOXes). The transport of thiamine and thiamine diphosphate between plant tissues and into cell compartments determines the proper functioning of major metabolic pathways such as the acetyl-CoA synthesis, the tricarboxylic acid cycle, the pentose phosphate pathway, Calvin–Benson cycle and isoprenoid biosynthesis pathway. The recently reported activation of thiamine production in plant cells under biotic or abiotic stress conditions also suggests a non-cofactor role of this vitamin as a stress alarmone or stress protectant to enable plants to survive in unfavourable environments.