Interplay between JA, SA and ABA signalling during basal and induced resistance against Pseudomonas syringae and Alternaria brassicicola

Abstract

SummaryWe have examined the role of the callose synthase PMR4 in basal resistance and b-aminobutyric acid-induced resistance (BABA-IR) of Arabidopsis thaliana against the hemi-biotrophic pathogen Pseudomonas syringae and the necrotrophic pathogen Alternaria brassicicola. Compared to wild-type plants, the pmr4-1 mutant displayed enhanced basal resistance against P. syringae, which correlated with constitutive expression of the PR-1 gene. Treating the pmr4-1 mutant with BABA boosted the already elevated levels of PR-1 gene expression, and further increased the level of resistance. Hence, BABA-IR against P. syringae does not require PMR4-derived callose. Conversely, pmr4-1 plants showed enhanced susceptibility to A. brassicicola, and failed to show BABA-IR. Wild-type plants showing BABA-IR against A. brassicicola produced increased levels of JA. The pmr4-1 mutant produced less JA upon A. brassicicola infection than the wild-type. Blocking SA accumulation in pmr4-1 restored basal resistance, but not BABA-IR against A. brassicicola. This suggests that the mutant's enhanced susceptibility to A. brassicicola is caused by SA-mediated suppression of JA, whereas the lack of BABA-IR is caused by its inability to produce callose. A. brassicicola infection suppressed ABA accumulation. Pre-treatment with BABA antagonized this ABA accumulation, and concurrently potentiated expression of the ABA-responsive ABI1 gene. Hence, BABA prevents pathogen-induced suppression of ABA accumulation, and sensitizes the tissue to ABA, causing augmented deposition of PMR4-derived callose.

Elevated Early Callose Deposition Results in Complete Penetration Resistance to Powdery Mildew in Arabidopsis

“…The expected induction of the salicylic acid pathway in a compatible interaction and of the jasmonate pathway in an incompatible interaction (Zimmerli et al, 2004) was only confirmed for the wild-type plant. Deregulation of the jasmonate pathway in the pmr4 mutant was previously shown in the interaction with the necrotrophic pathogen A. brassicicola (Flors et al, 2008), which indicates that the callose synthase PMR4 might have not only an enzymatic function but also a regulatory role. Indeed, our data for the noncellulosic monocarbohydrate composition of the cell wall support the latter idea.…”

The multifaceted role of ABA in disease resistance

“…Earlier findings demonstrated that P. syringae-induced callose deposition is suppressed by ABA [14]. However, multiple studies from different groups have demonstrated that ABA exerts a positive influence on callose deposition after infection by fungi [23,28,49,50]. Moreover, it was recently demonstrated [50] that the fungal PAMP chitosan promotes ABA synthesis and that chitosan-induced callose is inhibited by pre-treatment with an ABA inhibitor.…”

Arabidopsis PECTIN METHYLESTERASEs Contribute to Immunity against Pseudomonas syringae

“…The spores were washed from the surface of the plate with inoculation medium (1 3 Gamborg B5 [Sigma], 10 mM Suc, 10 mM KH 2 PO 4 ; Flors et al, 2008), and fungal hyphae were removed from the suspension by filtering through four layers of cheesecloth. The concentration of spores was determined using a hemacytometer and adjusted to 1 3 10 5 spores mL 21 for A. brassicicola growth assays and 1 3 10 6 spores mL 21 for PME activity and qRT-PCR assays.…”

“…Prior to each experiment Alternaria brassicicola strain ATCC96836 was grown on a modified potato dextrose agar medium (Flors et al, 2008) for 10 d at room temperature. The spores were washed from the surface of the plate with inoculation medium (1 3 Gamborg B5 [Sigma], 10 mM Suc, 10 mM KH 2 PO 4 ; Flors et al, 2008), and fungal hyphae were removed from the suspension by filtering through four layers of cheesecloth.…”