Jasmonate is involved in the induction of tyrosine aminotransferase and tocopherol biosynthesis in Arabidopsis thaliana

Abstract

Coronatine-inducible tyrosine aminotransferase (TAT), which catalyses the transamination from tyrosine to p-hydroxyphenylpyruvate, is the first enzyme of a pathway leading via homogentisic acid to plastoquinone and tocopherols, the latter of which are known to be radical scavengers in plants. TAT can be also induced by the octadecanoids methyl jasmonate (MeJA) and methyl-12-oxophytodienoic acid (MeOPDA), as well as by wounding, high light, UV light and the herbicide oxyfluorfen. In order to elucidate the role of octadecanoids in the process of TAT induction in Arabidopsis thaliana (L.) Heynh., the jasmonate-deficient mutant delayed dehiscence (dde1) was used, in which the gene for 12-oxophytodienoic acid reductase 3 is disrupted. The amount of immunodetectable TAT was low. The enzyme was still fully induced by coronatine as well as by MeJA although induction by the latter was to a lesser extent and later than in the wild type. Treatment with MeOPDA, wounding and UV light, however, had hardly any effects. Tocopherol levels that showed considerable increases in the wild type after some treatments were much less affected in the mutant. However, starting levels of tocopherol were higher in non-induced dde1 than in the wild type. We conclude that jasmonate plays an important role in the signal transduction pathway regulating TAT activity and the biosynthesis of its product tocopherol.

The Role of Homogentisate Phytyltransferase and Other Tocopherol Pathway Enzymes in the Regulation of Tocopherol Synthesis during Abiotic Stress

“…The aromatic precursor HGA is derived from prephenate or Tyr, both products of the shikimate pathway (Threlfall and Whistance, 1971;Fiedler et al, 1982;Lopukhina et al, 2001;Sandorf and Hollander-Czytko, 2002). In plants, the shikimate pathway has been shown to be regulated at the transcriptional level and globally up-regulated during biotic and abiotic stresses (Gorlach et al, 1995;Herrman and Weaver, 1999;Diaz et al, 2001).…”

“…HPPD activity limits tocopherol synthesis in non-stressed Arabidopsis plants (Tsegaye et al, 2002), and HPPD mRNA levels are up-regulated in senescing barley (Hordeum vulgare) leaves (KleblerJanke and Krupinska, 1997). Similarly, various biotic and abiotic stresses elevate Tyr aminotransferase (TAT) mRNA and protein levels and enzyme activity in Arabidopsis (Lopukhina et al, 2001;Sandorf and Hollander-Czytko, 2002). Whether other steps of the tocopherol pathway are also involved in the regulation of tocopherol biosynthesis during stress remains to be determined.…”

Functions of tocopherols in the cells of plants and other photosynthetic organisms

“…The promotion of POL leads to the formation of jasmonic acid -phytohormone that activates the expression of nuclear genes encoding enzymes of tocopherol synthesis [41,42]. However, strengthening of photo-and antioxidant protection in the cell may be insufficient for the plant could bear unfavorable conditions and does not stop its ageing.…”

“…3) [41]. Thus, if propagation of POL does not stop as a result of antioxidant action of membrane localized tocopherols, jasmonic acid level is increased.…”

Tyrosine Aminotransferase Contributes to Benzylisoquinoline Alkaloid Biosynthesis in Opium Poppy

“…The TAT3 gene (At2g24850; designated AtTyrAT-2 here) was shown to encode the enzyme catalyzing the first step in tocopherol biosynthesis and was induced by MeJA and methyl 12-oxophytodienoic acid, wounding, high light intensity, UV light, and the herbicide oxyfluorfen (Sandorf and Holländer-Czytko, 2002). The rooty/superroot1 gene (At2g20610; designated AtTyrAT-3 here) is a locus on Arabidopsis chromosome 2 encoding a protein suggested to have TyrAT activity (Gopalraj et al, 1996).…”