An evolutionarily ancient Fatty Acid Desaturase is required for the synthesis of hexadecatrienoic acid, which is the main source of the bioactive jasmonate in Marchantia polymorpha

Jasmonates are fatty acid derived hormones that regulate multiple aspects of plant development, growth and stress responses. Bioactive jasmonates, defined as the ligands of the conserved COI1 receptor, differ between vascular plants and bryophytes (using jasmonoyl-L-isoleucine; JA-Ile and dinor-12-oxo-10,15(Z)-phytodienoic acid; dn-OPDA, respectively). Whilst the biosynthetic pathways of JA-Ile in the model vascular plant Arabidopsis thaliana have been elucidated, the details of dn-OPDA biosynthesis in bryophytes are still unclear. Here, we identify an ortholog of Arabidopsis Fatty Acid Desaturase 5 (AtFAD5) in the model liverwort Marchantia polymorpha and show that FAD5 function is ancient and conserved between species separated by more than 450 million years of independent evolution. Similar to AtFAD5, MpFAD5 is required for the synthesis of 7Z-hexadecenoic acid. Consequently, in Mpfad5 mutants the hexadecanoid pathway is blocked, dn-OPDA levels almost completely depleted and normal chloroplast development is impaired. Our results demonstrate that the main source of dn-OPDA in Marchantia is the hexadecanoid pathway and the contribution of the octadecanoid pathway, i.e. from OPDA, is minimal. Remarkably, despite extremely low levels of dn-OPDA, MpCOI1-mediated responses to wounding and insect feeding can still be activated in Mpfad5, suggesting that dn-OPDA is not the only bioactive jasmonate and COI1 ligand in Marchantia.

The Algal Polysaccharide Ulvan Induces Resistance in Wheat Against Zymoseptoria tritici Without Major Alteration of Leaf Metabolome

This study aimed to examine the ability of ulvan, a water-soluble polysaccharide from the green seaweed Ulva fasciata, to provide protection and induce resistance in wheat against the hemibiotrophic fungus Zymoseptoria tritici. Matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) analysis indicated that ulvan is mainly composed of unsaturated monosaccharides (rhamnose, rhamnose-3-sulfate, and xylose) and numerous uronic acid residues. In the greenhouse, foliar application of ulvan at 10 mg.ml–1 2 days before fungal inoculation reduced disease severity and pycnidium density by 45 and 50%, respectively. Ulvan did not exhibit any direct antifungal activity toward Z. tritici, neither in vitro nor in planta. However, ulvan treatment significantly reduced substomatal colonization and pycnidium formation within the mesophyll of treated leaves. Molecular assays revealed that ulvan spraying elicits, but does not prime, the expression of genes involved in several wheat defense pathways, including pathogenesis-related proteins (β-1,3-endoglucanase and chitinase), reactive oxygen species metabolism (oxalate oxidase), and the octadecanoid pathway (lipoxygenase and allene oxide synthase), while no upregulation was recorded for gene markers of the phenylpropanoid pathway (phenylalanine ammonia-lyase and chalcone synthase). Interestingly, the quantification of 83 metabolites from major chemical families using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS) in both non-infectious and infectious conditions showed no substantial changes in wheat metabolome upon ulvan treatment, suggesting a low metabolic cost associated with ulvan-induced resistance. Our findings provide evidence that ulvan confers protection and triggers defense mechanisms in wheat against Z. tritici without major modification of the plant physiology.

Fatty acid desaturases modulated octadecanoid pathway in Sesame

Omega 3 fatty acid desaturases are involved in the production of α-linolenic acid (LNA) an essential omega 3 fatty acid, which is present in only traces in sesame seeds. LNA is the precursor for jasmonic acid which is the end product of octadecanoid pathway. This study was undertaken to analyze the key components of octadecanoid pathway and its relationship with fatty acid content in sesame. Fatty acid desaturation and membrane fluidity are modulated differentially in various stresses. Sesame seedlings were subjected to transient stress to analyse the octadecanoid pathway and its impact on fatty acid desaturation. The mRNA levels of omega 3 desaturases and LNA content were higher in cold stressed sesame seedlings than heat, drought and salinity stresses. The LOX activity and MDA content were higher in heat stressed sesame seedlings. Jasmonic acid content was higher in salinity stressed seedlings while abscisic acid registered the highest in drought stressed seedlings. Chloroplast fatty acid desaturase genes expression was found to increase the LNA content in cold stressed seedlings. The level of membrane damage measured by lipid peroxidation in terms of LOX activity and MDA content were found to be minimal in cold stressed seedling. This suggests a possible role of LNA in membrane fluidity and cold acclimation in sesame. A synergistic role of JA and ABA is also suspected in abiotic stress tolerance in sesame.

A Plant Nutrient- and Microbial Protein-Based Resistance Inducer Elicits Wheat Cultivar-Dependent Resistance Against Zymoseptoria tritici

The induction of plant defense mechanisms by resistance inducers is an attractive and innovative alternative to reduce the use of fungicides on wheat against Zymoseptoria tritici, the responsible agent of Septoria tritici blotch (STB). Under controlled conditions, we investigated the resistance induction in three wheat cultivars with different susceptible levels to STB as a response to a treatment with a sulfur, manganese sulfate, and protein-based resistance inducer (NECTAR Céréales). While no direct antigermination effect of the product was observed in planta, more than 50% reduction of both symptoms and sporulation were recorded on the three tested cultivars. However, an impact of the wheat genotype on resistance induction was highlighted, which affects host penetration, cell colonization, and the production of cell-wall degrading enzymes by the fungus. Moreover, in the most susceptible cultivar Alixan, the product upregulated POX2, PAL, PR1, and GLUC gene expression in both noninoculated and inoculated plants and CHIT2 in noninoculated plants only. In contrast, defense responses induced in Altigo, the most resistant cultivar, seem to be more specifically mediated by the phenylpropanoid pathway in noninoculated as well as inoculated plants, since PAL and CHS were most specifically upregulated in this cultivar. In Premio, the moderate resistant cultivar, NECTAR Céréales elicits mainly the octadecanoid pathway, via LOX and AOS induction in noninoculated plants. We concluded that this complex resistance-inducing product protects wheat against Z. tritici by stimulating the cultivar-dependent plant defense mechanisms.

Artemisinic Acid Serves as a Novel ORCA3 Inducer to Enhance Biosynthesis of Terpenoid Indole Alkaloids in Catharanthus roseus Cambial Meristematic Cells

To investigate the effect of artemisinic acid (AA) on improving the production of terpenoid indole alkaloids (TIAs) of Catharanthus roseus cambial meristematic cells (CMCs), feeding AA to C. roseus CMCs caused 2.35-fold and 2.51-fold increases in the production of vindoline and catharanthine, respectively, compared with those of the untreated CMCs. qRT-PCR experiments showed that AA resulted in a 1.36-8.52 fold increase in the transcript levels of several related genes, including octadecanoid-derivative responsive Catharanthus AP2-domain protein 3 (ORCA3), tryptophan decarboxylase (TDC), strictosidine synthase (STR) and desacetoxyvindoline 4-hydroxylase (D4H). However, no effect was observed on the concentration of either jasmonic acid (JA), or the octadecanoid-pathway inhibitors block TIA accumulation caused by AA. The results indicated that AA might serve as a novel ORCA3 inducer to manipulate biosynthesis of TIAs in C. roseus CMCs via an unknown mechanism.

Phosphatidic acid synthesis, octadecanoic pathway and fatty acids content as lipid markers of exogeneous salicylic acid-induced elicitation in wheat

Activators of plant defence responses against pathogens are a potential alternative to fungicides, and the well-known resistance inducer salicylic acid (SA) protects wheat (Triticum aestivum L.) against powdery mildew. The aim of our work was to investigate through biochemical and molecular approaches whether lipid metabolism alteration could be considered as a characteristic feature of induced resistance in wheat upon SA infiltration. Expression levels of lox, PI-PLC2 and ltp genes encoding for a lipoxygenase (LOX), a phospholipase C2 and a lipid-transfer protein, respectively, were investigated. Increase of phosphatidic acid (PA) content 48 h after SA infiltration in wheat leaves, upregulation of PI-PLC2 gene expression and increased diacylglycerol content were recorded, indicating the involvement of the PLC pathway in the PA synthesis. The wheat octadecanoid pathway was shown to be highly responsive to SA infiltration through simultaneous increases in lox gene expression and LOX activity, as well as a reduction in the content of linolenic acid. Changes in several FA contents and increases of the ltp gene expression were also recorded during the latest hours after SA infiltration. The status of lipid metabolism, as well as the connections between its components as markers of SA-induced resistance in wheat, are discussed.

Methyl jasmonate-induced cell death in grapevine requires both lipoxygenase activity and functional octadecanoid biosynthetic pathway

Grapevine (Vitis vinifera L., cv. Limberger) leaf tissues and suspension-cultured cells were induced to undergo programmed cell death (PCD) by exogenously added methyl jasmonate (MeJA). The elicitor signaling pathway involved in MeJA-induced PCD was further investigated using pharmacological, biochemical and histological approaches. Pharmacological dissection of the early events preceding the execution of MeJA-triggered PCD indicated that this process strongly depends on both, de novo protein and mRNA synthesis. Treatment of leaf discs and cell suspensions with lipase inhibitor Ebelactone B and specific lipoxygenase inhibitor Phenidone blocked MeJA-induced PCD. These results suggest that some chloroplast membrane-derived compound(s) is required for MeJA-induced PCD in grapevine. The progression of MeJAtriggered PCD may be further inhibited by the use of metabolic inhibitors of key enzymes of octadecanoid biosynthesis including AOS, AOC, and OPR indicating that the functional jasmonate biosynthetic pathway is an integral part of the MeJA-induced signal transduction cascade that results in the coordinate expression of events leading to PCD. Finally, the activation of the octadecanoid pathway, as a critical point in MeJA-induced PCD, was independently demonstrated with cellulysin, a macromolecular elicitor acting via octadecanoid signaling. The cellulysin was shown to be a very potent enhancer of MeJA-triggered PCD in grapevine cells.