A Role for Tocopherol Biosynthesis in Arabidopsis Basal Immunity to Bacterial Infection

Abstract

ORCID IDs: 0000-0003-4828-958X (M.H.); 0000-0002-9532-8687 (N.S.); 0000-0002-8703-5403 (J.Z.).Tocopherols are lipid-soluble antioxidants synthesized in plastids of plants and other photosynthetic organisms. The four known tocopherols, a-, b-, g-, and d-tocopherol, differ in number and position of methyl groups on their chromanol head group. In unstressed Arabidopsis (Arabidopsis thaliana) leaves, a-tocopherol constitutes the main tocopherol form, whereas seeds predominantly contain g-tocopherol. Here, we show that inoculation of Arabidopsis leaves with the bacterial pathogen Pseudomonas syringae induces the expression of genes involved in early steps of tocopherol biosynthesis and triggers strong accumulation of g-tocopherol, moderate production of d-tocopherol, and generation of the benzoquinol precursors of tocopherols. The pathogen-inducible biosynthesis of tocopherols is promoted by the immune regulators ENHANCED DISEASE SUSCEPTIBILITY1 and PHYTOALEXIN-DEFICIENT4. In addition, tocopherols accumulate in response to bacterial flagellin and reactive oxygen species. By quantifying tocopherol forms in inoculated wild-type plants and biosynthetic pathway mutants, we provide biochemical insights into the pathogen-inducible tocopherol pathway. Notably, vitamin E deficient2 (vte2) mutant plants, which are compromised in both tocopherol and benzoquinol precursor accumulation, exhibit increased susceptibility toward compatible P. syringae and possess heightened levels of markers of lipid peroxidation after bacterial infection. The deficiency of triunsaturated fatty acids in vte2-1 fatty acid desaturase3-2 (fad3-2) fad7-2 fad8 quadruple mutants prevents increased lipid peroxidation in the vte2 background and restores pathogen resistance to wild-type levels. Therefore, the tocopherol biosynthetic pathway positively influences salicylic acid accumulation and guarantees effective basal resistance of Arabidopsis against compatible P. syringae, possibly by protecting leaves from the pathogen-induced oxidation of trienoic fatty acid-containing lipids.

Inducible biosynthesis and immune function of the systemic acquired resistance inducer N-hydroxypipecolic acid in monocotyledonous and dicotyledonous plants

“…To determine the levels of Pip, NHP, SA, SAG, NHP-hexose, and lysine in the leaves of the different species, the gas chromatography-mass spectrometry-based analytical procedure previously established for Arabidopsis was used (detailed in Hartmann et al , 2018 ; Stahl et al , 2019 ). For metabolic analyses of cucumber phloem sap, the above-described filter paper extracts were supplemented with 900 µl of MeOH/H 2 O (80:20, v/v) and analysed.…”

Shifting paradigms and novel players in Cys-based redox regulation and ROS signaling in plants - and where to go next

“…If not removed immediately, PL-OOH can undergo fragmentation to form highly toxic lipid radicals and other reactive lipid breakdown products (Schneider et al 2008). Non-enzymatic systems preventing uncontrolled accumulation of PL-OOH include chelators of iron and lipophilic radical-trapping antioxidants, especially ɑ-and ɣ-tocopherol (Kanwischer et al 2005;Stahl et al 2019;. In contrast to the primary function of tocopherols at the plasma membrane in mammalian cells, their protective function in plants, however, is primarily exerted at the chloroplast membrane (Maeda and DellaPenna 2007).…”

Validated MAGIC and GWAS population mapping reveals the link between vitamin E content and natural variation in chorismate metabolism in tomato

“…The production of these molecules is a metabolic innovation allowing plants to live under high-oxygen conditions (Das and Roychoudhury, 2014), as their roles protecting photosystem II against oxygen singlets and limiting lipid peroxidation are well documented (Krieger-Liszkay and Trebst, 2006;Miret and Munné-Bosch, 2015). More recently, it was demonstrated that the tocopherol biosynthetic pathway modulates salicylic acid accumulation, affecting basal resistance against Pseudomonas syringae in Arabidopsis plants (Stahl et al, 2019). Furthermore, tocopherols were found to be required for a retrograde chloroplast-to-nucleus signaling mechanism favoring micro RNA biogenesis under abiotic stress (Fang et al, 2019).…”