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Genetic Engineering of Plant Seeds to Increase Thiamin (Vitamin B1) Content
Biochemistry and Molecular Biology
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Thiamine (Vitamin B1) in the form of thiamine pyrophosphate (TPP) is an essential cofactor for the function of numerous enzymes which are involved in central metabolism such as citric acid cycle, pentose phosphate pathway, Calvin cycle, isoprenoid biosynthesis, and branched-chain amino acid biosynthesis. All living organisms need thiamine. However, human and animals can synthesize TPP from thiamine, but they are not able to synthesize thiamine de novo. Therefore, human and animals must obtain thiamine from their diet to maintain a normal metabolism. Severe thiamine deficiency causes the lethal disease beriberi and Wernicke-Korsakoff syndrome in humans. The enzymes involved in thiamine de novo biosynthesis pathway are well known in microorganisms and plants, but little is known regarding the salvage pathways in plants. In order to have better insight about the thiamine salvage pathways in plants, the homologs of bacterial ThiM (thiazole kinase) were analyzed. It has been revealed that this protein in plants has thazole kinase activity which is important for thiamine salvage. In addition, analyzing the TenA_E proteins in plants shows that these proteins have amidohydrolase and aminohydrolase activity to form 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) from the salvage of thiamine breakdown products. Thiamine plays a vital role in resistance against biotic and abiotic stresses in plants in addition to its role as a cofactor. It has been shown that elevated levels of thiamine content achieved by the seed overexpression of Thi4, ThiC, and ThiE genes can enhance the seed germination and seedlings viability under abiotic stress conditions. Additionally, thiamine and TPP over-producing lines shows altered seed carbon partitioning.