Article

Tocopherols Modulate Extraplastidic Polyunsaturated Fatty Acid Metabolism in Arabidopsis at Low Temperature

Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA.
The Plant Cell (Impact Factor: 9.34). 03/2008; 20(2):452-70. DOI: 10.1105/tpc.107.054718
Source: PubMed

ABSTRACT

Tocopherols (vitamin E) are synthesized in plastids and have long been assumed to have essential functions restricted to these organelles. We previously reported that the vitamin e-deficient2 (vte2) mutant of Arabidopsis thaliana is defective in transfer cell wall development and photoassimilate transport at low temperature (LT). Here, we demonstrate that LT-treated vte2 has a distinct composition of polyunsaturated fatty acids (PUFAs): lower levels of linolenic acid (18:3) and higher levels of linoleic acid (18:2) compared with the wild type. Enhanced 18:3 oxidation was not involved, as indicated by the limited differences in oxidized lipid species between LT-treated vte2 and the wild type and by a lack of impact on the LT-induced vte2 phenotype in a vte2 fad3 fad7 fad8 quadruple mutant deficient in 18:3. PUFA changes in LT-treated vte2 occur primarily in phospholipids due to reduced conversion of dienoic to trienoic fatty acids in the endoplasmic reticulum (ER) pathway. Introduction of the ER fatty acid desaturase mutation, fad2, and to a lesser extent the plastidic fad6 mutation into the vte2 background suppressed the LT-induced vte2 phenotypes, including abnormal transfer cell wall development. These results provide biochemical and genetic evidence that plastid-synthesized tocopherols modulate ER PUFA metabolism early in the LT adaptation response of Arabidopsis.

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    • "Tocopherols, as part of the photoprotective machinery , are particularly involved in controlling the level of 1 O 2 in photosystem II (PSII), and the extent of lipid peroxidation in thylakoid membranes especially under stress conditions (Triantaphylidès and Havaux, 2009; Rastogi et al., 2014; Miret and Munné-Bosch, 2015). Beyond photoprotective roles, tocopherol is also involved in seed longevity, seedling germination (Sattler et al., 2004; Mène-Saffrané et al., 2010), and photoassimilate export (Maeda et al., 2006, 2008; Asensi- Fabado et al., 2014); although, for the latter, the precise underlying mechanism remains elusive (Maeda et al., 2014). "
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    ABSTRACT: Tocopherol, a compound with vitamin E (VTE) activity, is a conserved constituent of the plastidial antioxidant network in photosynthetic organisms. The synthesis of tocopherol involves the condensation of an aromatic head group with an isoprenoid prenyl side chain. The latter, phytyl diphosphate, can be derived from chlorophyll phytol tail recycling, which depends on phytol kinase (VTE5) activity. How plants co-ordinate isoprenoid precursor distribution for supplying biosynthesis of tocopherol and other prenyllipids in different organs is poorly understood. Here, Solanum lycopersicum plants impaired in the expression of two VTE5-like genes identified by phylogenetic analyses, named SlVTE5 and SlFOLK, were characterized. Our data show that while SlFOLK does not affect tocopherol content, the production of this metabolite is >80% dependent on SlVTE5 in tomato, in both leaves and fruits. VTE5 deficiency greatly impacted lipid metabolism, including prenylquinones, carotenoids, and fatty acid phytyl esters. However, the prenyllipid profile greatly differed between source and sink organs, revealing organ-specific metabolic adjustments in tomato. Additionally, VTE5-deficient plants displayed starch accumulation and lower CO2 assimilation in leaves associated with mild yield penalty. Taken together, our results provide valuable insights into the distinct regulation of isoprenoid metabolism in leaves and fruits and also expose the interaction between lipid and carbon metabolism, which results in carbohydrate export blockage in the VTE5-deficient plants, affecting tomato fruit quality.
    Full-text · Article · Nov 2015 · Journal of Experimental Botany
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    • "Transgenic plants lacking tocopherols are impaired in photoassimilate export and present altered expression of photosynthetic and defence-related genes (Hofius et al., 2004). Besides, tocopherols affect gene expression by modulating the extraplastidic PUFA metabolism, which is essential for seedlings germination and growth (Sattler et al., 2004Sattler et al., , 2006), and low temperature acclimation (Maeda et al., 2006Maeda et al., , 2008Song et al., 2010). Recently, a role for -tocopherol in the regulation of jasmonic acid and ethylene signalling pathways under salt stress has been shown (Cela et al., 2011). "
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    ABSTRACT: Homogentisate phytyltransferase (HPT) (EC 2.5.1.-) catalyzes the first committed step of tocopherol biosynthesis in all photosynthetic organisms. This paper presents the molecular characterization and expression analysis of HPT1 gene, and a study on the accumulation of tocopherols under different environmental conditions in the unicellular green alga Chlamydomonas reinhardtii. The Chlamydomonas HPT1 protein conserves all the prenylphosphate- and divalent cation-binding sites that are found in polyprenyltransferases and all the amino acids that are essential for its catalytic activity. Its hydrophobicity profile confirms that HPT is a membrane-bound protein. Chlamydomonas genomic DNA analysis suggests that HPT is encoded by a single gene, HPT1, whose promoter region contains multiple motifs related to regulation by jasmonate, abscisic acid, low temperature and light, and an ATCTA motif presents in genes involved in tocopherol biosynthesis and some photosynthesis-related genes. Expression analysis revealed that HPT1 is strongly regulated by dark and low-temperature. Under the same treatments, α-tocopherol increased in cultures exposed to darkness or heat, whereas γ-tocopherol did it in low temperature. The regulatory expression pattern of HPT1 and the changes of tocopherol abundance support the idea that different tocopherols play specific functions, and suggest a role for γ-tocopherol in the adaptation to growth under low-temperature.
    Full-text · Article · Sep 2015 · Journal of plant physiology
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    • ". These alterations are suppressed by the mutation of the ER FATTY ACID DESATURASE 2 gene (fad2), which also suppresses all of the LT-induced vte2 phenotypes (Maeda et al., 2008; Song et al., 2010). Subsequent vasculature-specific callose deposition is primarily mediated by the GSL5 enzyme and tocopherol-deficiency affects its activity post-transcriptionally. "
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    ABSTRACT: Tocopherols (vitamin E) are lipid-soluble antioxidants produced by all plants and algae, and many cyanobacteria, yet their functions in these photosynthetic organisms are still not fully understood. We have previously reported that the vitamin E deficient 2 (vte2) mutant of Arabidopsis thaliana is sensitive to low temperature (LT) due to impaired transfer cell wall (TCW) development and photoassimilate export associated with massive callose deposition in transfer cells of the phloem. To further understand the roles of tocopherols in LT induced TCW development we compared the global transcript profiles of vte2 and wild-type leaves during LT treatment. Tocopherol deficiency had no significant impact on global gene expression in permissive conditions, but significantly affected expression of 77 genes after 48 h of LT treatment. In vte2 relative to wild type, genes associated with solute transport were repressed, while those involved in various pathogen responses and cell wall modifications, including two members of callose synthase gene family, GLUCAN SYNTHASE LIKE 4 (GSL4) and GSL11, were induced. However, introduction of gsl4 or gsl11 mutations individually into the vte2 background did not suppress callose deposition or the overall LT-induced phenotypes of vte2. Intriguingly, introduction of a mutation disrupting GSL5, the major GSL responsible for pathogen-induced callose deposition, into vte2 substantially reduced vascular callose deposition at LT, but again had no effect on the photoassimilate export phenotype of LT-treated vte2. These results suggest that GSL5 plays a major role in TCW callose deposition in LT-treated vte2 but that this GSL5-dependent callose deposition is not the primary cause of the impaired photoassimilate export phenotype.
    Full-text · Article · Feb 2014 · Frontiers in Plant Science
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