Gentisic Acid As a Pathogen-Inducible Signal, Additional to Salicylic Acid for Activation of Plant Defenses in Tomato

Abstract

Citrus exocortis viroid (CEVd) and tomato mosaic virus (ToMV), which produce a systemic non-necrotizing infection in tomato (Lycopersicon esculentum cv. Rutgers), strongly induced the accumulation of a phenolic compound that we have characterized as 2,5-dihydroxybenzoic acid (gentisic acid, GA) by nuclear magnetic resonance, following purification by high-performance liquid chromatography. Levels of free and total GA increased more than 150-fold in response to CEVd and ToMV infections. Unlike these non-necrotizing infections, the necrotizing reaction elicited by Pseudomonas syringae pv. syringae in this host did not produce any accumulation of GA. It is also shown that, in healthy leaf tissues, benzoic acid (BA) and salicylic acid (SA) were rapidly converted to GA, SA being the immediate precursor of GA, according to radiolabeling studies. Interestingly, exogenous GA elicited accumulation of the previously described CEVd-induced antifungal pathogenesis-related (PR) proteins P23, P32, and P34. These proteins were not induced by exogenous SA, which is able to elicit other CEVd-induced PR proteins in tomato. These results suggest that GA acts as a pathogeninduced signal, additional to SA, for activation of plant defense genes in tomato.

Accumulation of Isochorismate-derived 2,3-Dihydroxybenzoic 3-O-β-d-Xyloside in Arabidopsis Resistance to Pathogens and Ageing of Leaves

“…2,3-DHBA levels increased in Catharanthus roseus cell suspension and shoot cultures in response to elicitors (40). Also 2,5-DHBA accumulation was reported in tomato plants upon viral infection (41). In plants, both 2,3-DHBA and 2,5-DHBA are thought to be derived from the shikimate pathway via isochorismate, as established in bacteria (14,42,43).…”

Exploiting Natural Variation of Secondary Metabolism Identifies a Gene Controlling the Glycosylation Diversity of Dihydroxybenzoic Acids in Arabidopsis thaliana

“…DHBA glycoside biosynthesis has been implicated in defense responses and leaf senescence regulation (Belles et al 1999;Fayos et al 2006;Bartsch et al 2010;Zhang et al 2013), but it is yet unclear whether these are due to modulation of SA activity or new activities conferred by DHBAs and/or their glycosides. Glycosylation is a common modification that contributes to the diversity of secondary metabolism.…”

“…DHBA glycosides may serve as an inactive storage form, parallel to the role of SA b-glucoside for SA (Chen et al 1995). Alternatively, the sugar moiety of DHBA glycosides may be important for their suggested signaling activity in plant defense (Belles et al 1999;Bartsch et al 2010). There are known cases where the sugar moiety of a glycoside has been shown to be important for the biological activity of the molecule.…”

Identification of defence metabolites in tomato plants infected by the bacterial pathogen Pseudomonas syringae

“…Two observations, based both on previously reported results (Reinhardt et al, 1991) and other presented here, prompted us to search for the possible role of endogenous ethylene on HCAA induction observed here: a) Rutgers tomato leaves produced a rapid (ca. 4 h after inoculation) and sharp elevation of ethylene synthesis upon infection with P. syringae 620 (Bellés et al, 1999), which preceded accumulation of metabolites that occurred at 24-48 h postinoculation, and b) although with lower increments than in P. syringae-infected leaves, HCAA were also found to be substantially elicited 24 h after application of 50 μl l -1 exogenous ethylene (Fig. 3A), while CGA and rutin strongly and rapidly (4 h after treatment) augmented in response to the same ethylene treatment (Fig.…”