Volatile C6-aldehydes and Allo-ocimene Activate Defense Genes and Induce Resistance against Botrytis cinerea in Arabidopsis thaliana

Abstract

Green leafy volatiles or isoprenoids are produced after mechanical wounding or pathogen/herbivore attacks in higher plants. We monitored expression profiles of the genes involved in defense responses upon exposing Arabidopsis thaliana to the volatiles. Among the genes investigated, those known to be induced by mechanical wounding and/or jasmonate application, such as chalcone synthase (CHS), caffeic acid-O-methyltransferase (COMT), diacylglycerol kinase1 (DGK1), glutathione-S-transferase1 (GST1) and lipoxygenase2 (LOX2), were shown to be induced with (E)-2-hexenal, (Z)-3-hexenal, (Z)-3-hexenol or allo-ocimene (2,6-dimethyl-2,4,6-octatriene). A salicylic acid-responsive gene, pathogenesis-related protein2 (PR2), was not induced by the volatiles. Detailed analyses of the expression profiles showed that the manner of induction varied depending on either the gene monitored or the volatile used. A chemically inert compound, (Z)-3-hexenol, was also potent, which suggested that chemical reactivity was not the sole requisite for the inducing activity. With a jasmonate-insensitive mutant (jar1), the induction by the volatiles was mostly suppressed, however, that of LOX2 was unaltered. An ethylene-insensitive mutant (etr1) showed responses almost identical to the wild type, with minor exceptions. From these observations, it was suggested that both the jasmonate-dependent and -independent pathways were operative upon perception of the volatiles, while the ETR1-dependent pathway was not directly involved. When Botrytis cinerea was inoculated after the volatile treatment, retardation of disease development could be seen. It appears that volatile treatment could make the plants more resistant against the fungal disease.

Airborne Induction and Priming of Plant Defenses against a Bacterial Pathogen

“…Which VOCs, then, were responsible for the responses that we observed? Green-leaf volatiles have repeatedly been reported to be active in airborne induction of herbivore resistance (Engelberth et al, 2004;Farag et al, 2005;Ruther and Kleier, 2005;Mirabella et al, 2008), and they can also enhance a plant's direct resistance to certain pathogens, particularly necrotrophic fungi (Kishimoto et al, 2005;Matsui, 2006;Shiojiri et al, 2006). Certain volatiles even might be involved in the resistance of plants to abiotic stress (Behnke et al, 2007), and BTH treatment has been reported to enhance the attractiveness of herbivore-damaged corn seedlings to parasitic wasps (Rostás and Turlings, 2008).…”

“…Furthermore, exposure to VOCs such as trans-2-hexenal, cis-3-hexenal, or cis-3-hexenol enhanced resistance of Arabidopsis against the fungal pathogen Botrytis cinerea (Kishimoto et al, 2005), which indicates that VOCs may also induce disease resistance. However, the wound response, the induction of VOCs, the effects of plant growth-promoting rhizobacteria, and even the resistance to necrotrophic pathogens such as B. cinerea and Alternaria brassiccicola are mediated via JA signaling (Wasternack and Parthier, 1997;Pieterse et al, 1998;Schilmiller and Howe, 2005;Francia et al, 2007;Heil, 2008;Heil and Ton, 2008).…”

A Catalase-related Hemoprotein in Coral Is Specialized for Synthesis of Short-chain Aldehydes

“…The (3Z)-hexenal and 12-oxo-cis-dodecenoic acid formed by 13-HPL have the capability to isomerize non-enzymatically (43) or by the isomerases (44,45) to biologically active forms, 2E-hexenal and 12-oxo-trans-dodecenoic acid (also known as traumatin), respectively. Traumatin plays an important role in plant wound healing (46), and 2(E)-hexenal induces the expression of HPL, AOS, LOX (47,48), and other stress genes in plants (49). Moreover, the electrophilic ␣,␤-unsaturated carbonyl group of aldehydes might interact with nucleophiles in biological systems (50,51), and in plants, antimicrobial properties of oxylipins including 2(E)-hexenal have been presented by Prost et al (52).…”

“…There are few possible interpretations of this apparent lack of enhancement of the cHPL-LOX activity; (i) in contrast to its plant counterpart, the cHPL may not be involved in a response to mechanical injury, and (ii) given that plant oxylipin synthesis is activated within seconds or a few minutes of wounding (54,55), a short-lived increase in the cHPL-LOX products may occur immediately after wounding, which has not been analyzed (16,53). Activation of the plant HPL pathway is associated with changes in the expression of other defense genes (47,49,56), and equivalent experiments to explore effects of the coral lyase products are required to elucidate the role of cHPL-LOX pathway.…”

Floral sesquiterpenes and their synthesis in dioecious kiwifruit

“…1 Terpenoids are a class of volatile secondary compounds that fulfill many ecological roles in plants interacting with their biotic environment, including pollinator attraction, direct and indirect defense against insects, bacteria, fungi and even mammals, 2 as well as in intraand inter-plant signaling. 3,4 Terpenes are produced from a small number of simple prenyl diphosphate substrates, but terpene synthase (TPS) enzymes are capable of producing many terpene skeletons. 2 Complexity is further increased by the action of several modifying enzymes leading to the production of even larger numbers of volatile secondary metabolites.…”