role of homogentisate phytyltransferase and other tocopherol pathway enzymes in the regulation of tocopherol synthesis during abiotic stress

• Published in: Plant physiology (Bethesda) Vol. 133; no. 2; pp. 930 - 940
• Main Authors: Collakova, E, DellaPenna, D
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.10.2003; American Society of Plant Physiologists; The American Society for Plant Biologists
• Subjects: abiotic stress; Adaptation to environment and cultivation conditions; Agronomy. Soil science and plant productions; alkyl (aryl) transferases; Alkyl and Aryl Transferases - metabolism; alpha-tocopherol; Animal and plant ecology; Animal, plant and microbial ecology; Anthocyanins - metabolism; antioxidants; Arabidopsis - enzymology; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Autoecology; Base Sequence; biochemical pathways; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Biosynthesis; Cell biochemistry; Cell physiology; Chlorophylls; Chloroplasts; Dimethylallyltranstransferase - metabolism; DNA Primers; Enzymes; Fundamental and applied biological sciences. Psychology; gamma-tocopherol; Gene expression regulation; gene overexpression; Genetics and breeding of economic plants; homogentisate phytyltransferase; hpt1 gene; Kinetics; Leaves; Messenger RNA; methyltransferases; molecular sequence data; nucleotide sequences; Oligonucleotide Probes; Oxidative stress; phytylquinol; Plant growth; Plant physiology and development; plant proteins; plant response; plant stress; Plants; Plants and fungi; Polymerase Chain Reaction; Protein Prenylation; Tocopherols; Tocopherols - metabolism; transgenic plants; Varietal selection. Specialized plant breeding, plant breeding aims; Gene overexpression; Biosynthesis; Metabolic pathway; Arabidopsis thaliana; Regulation(control); Enzymatic activity; Cruciferae; Dicotyledones; Angiospermae; Chemical concentration; Transgenic plant; Intraspecific comparison; Enzyme; Transferases; Genetic variant; Antioxidant; Stress; Methyltransferases; Limiting factor; Spermatophyta; Mutation; Experimental plant; Biological accumulation; Methylation; Tocopherol
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.103.026138

Tocopherols are amphipathic antioxidants synthesized exclusively by photosynthetic organisms. Tocopherol levels change significantly during plant growth and development and in response to stress, likely as a consequence of the altered expression of pathway-related genes. Homogentisate phytyltransferase (HPT) is a key enzyme limiting tocopherol biosynthesis in unstressed Arabidopsis leaves (E. Collakova, D. DellaPenna [2003] Plant Physiol 131: 632-642). Wild-type and transgenic Arabidopsis plants constitutively overexpressing HPT (35S::HPT1) were subjected to a combination of abiotic stresses for up to 15 d and tocopherol levels, composition, and expression of several tocopherol pathway-related genes were determined. Abiotic stress resulted in an 18- and 8-fold increase in total tocopherol content in wild-type and 35S::HPT1 leaves, respectively, with tocopherol levels in 35S::HPT1 being 2- to 4-fold higher than wild type at all experimental time points. Increased total tocopherol levels correlated with elevated HPT mRNA levels and HPT specific activity in 35S::HPT1 and wild-type leaves, suggesting that HPT activity limits total tocopherol synthesis during abiotic stress. In addition, substrate availability and expression of pathway enzymes before HPT also contribute to increased tocopherol synthesis during stress. The accumulation of high levels of beta-, gamma-, and delta-tocopherols in stressed tissues suggested that the methylation of phytylquinol and tocopherol intermediates limit alpha-tocopherol synthesis. Overexpression of gamma-tocopherol methyltransferase in the 35S::HPT1 background resulted in nearly complete conversion of gamma- and delta-tocopherols to alpha- and beta-tocopherols, respectively, indicating that gamma-tocopherol methyltransferase activity limits alpha-tocopherol synthesis in stressed leaves.