One shot-two pathogens blocked: exposure of Arabidopsis to hexadecane, a long chain volatile organic compound, confers induced resistance against both Pectobacterium carotovorum and Pseudomonas syringae

Abstract

Bacteria and plant derived volatile organic compounds have been reported as the chemical triggers that elicit induced resistance in plants. Previously, volatile organic compounds (VOCs), including acetoin and 2,3-butanediol, were found to be emitted from plant growth-promoting rhizobacteria (PGPR) Bacillus subtilis GB03, which had been shown to elicit ISR and plant growth promotion. More recently, we reported data that stronger induced resistance could be elicited against Pseudomonas syringae pv maculicola ES4326 in plants exposed to C13 VOC from another PGPR Paenibacillus polymyxa E681 compared with that of strain GB03. Here, we assessed whether another long hydrocarbon C16 hexadecane (HD) conferred protection to Arabidopsis from infection of a biotrophic pathogen, P. syringae pv maculicola and a necrotrophic pathogen, Pectobacterium carotovorum subsp carotovorum. Collectively, long-chain VOCs can be linked to a plant resistance activator for protecting plants against both biotrophic and necrotrophic pathogens at the same time.

Keywords: PGPR; Paenibacillus polymyxa; Pseudomonas syringae; induced systemic resistance; volatile organic compound.

Figure 1. Induced systemic resistance against Pseudomonas syringae pv maculicola ES4326 and Penctobacterium carotovorum subsp carotovorum and plant growth promotion by Paenibacillus polymyxa E681 and bacterial volatile hexadecane. (A) Chemical structure of hexadecane. (B) Induced systemic resistance against P. syringae pv maculicola ES4326 elicited by P. polymyxa E681, 10 mM, 100 μM and 1 μM hexadecane and 0.33 mM BTH using the I-plate system. Disease severity (0 = no symptom, 5 = severe chlorosis) was recorded seven days after pathogen challenge at 10⁸ cfu/ml on the leaves at 7 d after application of strain E681 and chemicals in roots. (C) Induced systemic resistance against P. carotovorum subsp carotovorum SCC1 elicited by P. polymyxa E681, 10 mM, 100 μM and 1 μM hexadecane and 0.33 mM BTH using the I-plate system. Disease severity (0 = no symptom, 5 = complete soft-rot) was recorded 24 h after drop-inoculation of pathogen at 10⁷ cfu/ml. (D) Plant growth responses by by P. polymyxa E681, 10 mM, 100 μM and 1 μM hexadecane and 0.33 mM BTH using the I-plate system. Sterile distilled water used as “control.” Different letters indicate significant differences between treatments, according to least significant difference at p = 0.05.