Concomitant Activation of Jasmonate and Ethylene Response Pathways Is Required for Induction of a Plant Defensin Gene in Arabidopsis

Abstract

Activation of the plant defensin gene PDF1.2 in Arabidopsis by pathogens has been shown previously to be blocked in the ethylene response mutant ein2-1 and the jasmonate response mutant coi1-1. In this work, we have further investigated the interactions between the ethylene and jasmonate signal pathways for the induction of this defense response. Inoculation of wild-type Arabidopsis plants with the fungus Alternaria brassicicola led to a marked increase in production of jasmonic acid, and this response was not blocked in the ein2-1 mutant. Likewise, A. brassicicola infection caused stimulated emission of ethylene both in wild-type plants and in coi1-1 mutants. However, treatment of either ein2-1 or coi1-1 mutants with methyl jasmonate or ethylene did not induce PDF1.2 , as it did in wild-type plants. We conclude from these experiments that both the ethylene and jasmonate signaling pathways need to be triggered concomitantly, and not sequentially, to activate PDF1.2 upon pathogen infection. In support of this idea, we observed a marked synergy between ethylene and methyl jasmonate for the induction of PDF1.2 in plants grown under sterile conditions. In contrast to the clear interdependence of the ethylene and jasmonate pathways for pathogen-induced activation of PDF1.2 , functional ethylene and jasmonate signaling pathways are not required for growth responses induced by jasmonate and ethylene, respectively. INTRODUCTIONHigher plants induce various defense responses when they are attacked by microbial pathogens, such as fungi, bacteria, or viruses. These defense responses include suicide of the attacked host cell (the so-called hypersensitive response); the production of antimicrobial secondary metabolites (called phytoalexins); the production of pathogenesisrelated (PR) proteins, of which many exert antimicrobial properties; and the production and oxidative cross-linking of cell wall polymers. The efficacy of these defense responses often determines whether plants are susceptible to infection by a pathogen.Elicitors secreted by or released from microbial invaders are the primary signal for induction of plant defense responses (Ebel and Cosio, 1994). Each pathogen produces a particular mixture of elicitors, which are sometimes accompanied by suppressors, and these molecules interact with receptors on the host cells that further translate the primary signal into particular events in the plasma membrane, the cytosol, and/or the nucleus (Shirasu et al., 1996). Induction of some defense genes requires the generation of secondary endogenous signal molecules (stress hormones) by the challenged cells in the infection site. The secondary signal molecules in turn set in motion signal transduction cascades in receiving cells, eventually leading to activation of pathogen-responsive genes. Secondary signal molecules thus serve to amplify and spread the response of the host after initial recognition of the pathogen. Several secondary signal molecules whose synthesis is increased in response to elicitor recognition and that ar...

Comparison of nicotinamide adenine dinucleotide phosphate-induced immune responses against biotrophic and necrotrophic pathogens in Arabidopsis thaliana

“…Expression levels of the SA pathway marker genes PR1, PR2, and PR5 and the JA/ET signaling marker genes PLANT DEFENSIN1.2 (PDF1.2), PR4, and BASIC CHITINASE (ChiB) in the samples were examined by real-time quantitative PCR. [5][6][7][8] Confirming the previous results, 1 NADP addition significantly induced the SA pathway marker genes (Fig. 1A).…”

“…1B). A time course experiment confirmed that PDF1.2 was not induced at several times (8,16, and 24 hr) when the PR1 gene was significanty activated (Fig. 1C).…”

Structural and expressional divergence of genes encoding O-methyltransferase in wheat

“…The methoxyflavone tricin acts as an antifeedant in Poaceae (Simmonds 2003), and phenolic compounds, such as quercetin or caffeic acid, are highly effective antioxidants in response to UV irradiation. Jasmonate (JA) and ethylene are considered to be critical signal molecules in wounding signal transduction that simultaneously or individually trigger an increase in the expression of defense-related genes (Penninckx et al 1998). Therefore, the wound-inducible TaOMT1 gene might be coordinately regulated by JA and ethylene.…”

Evaluation of a <i>Brassica napus</i> Auxin-Repressed Gene Induced by Flea Beetle Damage and <i>Sclerotinia sclerotiorum</i> Infection

“…JA and ethylene can be either synergistic or antagonistic hormones in terms of the expression of defensive genes in response to insect attack [5] [6] [7] [8], while both of these hormones mediate against pathogen attack (partly by defense gene induction) [9]. Curiously, plants deficient in ethylene signaling show either increased susceptibility or increased resistance, depending on the plant and pathogen [10].…”