The role of homogentisate phytyltransferase and other tocopherol pathway enzymes in the regulation of tocopherol synthesis during abiotic stress
The role of homogentisate phytyltransferase and other tocopherol pathway enzymes in the regulation of tocopherol synthesis during abiotic stress
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DOI：
10.1104/pp.103.026138
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发表时间：
2003-10-01
期刊：
影响因子：
7.4
通讯作者：
DellaPenna, D
中科院分区：
文献类型：
--
作者：
Collakova, E;DellaPenna, D
生育酚是专由光合生物合成的两亲性抗氧化剂。生育酚水平在植物生长和发育过程中以及对胁迫的响应中发生显著变化，这可能是途径相关基因表达改变的结果。在拟南芥（E. Collakova，D. DellaPenna [2003] Plant Physiol 131：632-642）。野生型和转基因拟南芥植物组成型过表达HPT（35 S：：HPT 1）进行了长达15天的非生物胁迫的组合和生育酚水平，组成，和几个生育酚途径相关基因的表达进行了测定。非生物胁迫导致野生型和35 S：：HPT 1叶中的总生育酚含量分别增加18倍和8倍，在所有实验时间点，35 S：：HPT 1中的生育酚水平比野生型高2至4倍。在35 S：：HPT 1和野生型叶片中，总生育酚水平的增加与HPT mRNA水平和HPT比活性的升高相关，表明HPT活性限制了非生物胁迫期间总生育酚的合成。此外，底物的可用性和HPT前途径酶的表达也有助于增加生育酚合成过程中的压力。高水平的β-、γ-和δ-生育酚在应激组织中的积累表明植醌和生育酚中间体的甲基化限制了α-生育酚的合成。γ-生育酚甲基转移酶在35 S：：HPT 1背景下的过表达导致γ-和δ-生育酚分别几乎完全转化为α-和β-生育酚，表明γ-生育酚甲基转移酶活性限制了胁迫叶片中的α-生育酚合成。
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 a-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.