The Plant Growth–Promoting Rhizobacterium Bacillus cereus AR156 Induces Systemic Resistance in Arabidopsis thaliana by Simultaneously Activating Salicylate- and Jasmonate/Ethylene-Dependent Signaling Pathways

Abstract

Bacillus cereus AR156 is a plant growth-promoting rhizobacterium that induces resistance against a broad spectrum of pathogens including Pseudomonas syringae pv. tomato DC3000. This study analyzed AR156-induced systemic resistance (ISR) to DC3000 in Arabidopsis ecotype Col-0 plants. Compared with mock-treated plants, AR156-treated ones showed an increase in biomass and reductions in disease severity and pathogen density in the leaves. The defense-related genes PR1, PR2, PR5, and PDF1.2 were concurrently expressed in the leaves of AR156-treated plants, suggesting simultaneous activation of the salicylic acid (SA)- and the jasmonic acid (JA)- and ethylene (ET)-dependent signaling pathways by AR156. The above gene expression was faster and stronger in plants treated with AR156 and inoculated with DC3000 than that in plants only inoculated with DC3000. Moreover, the cellular defense responses hydrogen peroxide accumulation and callose deposition were induced upon challenge inoculation in the leaves of Col-0 plants primed by AR156. Also, pretreatment with AR156 led to a higher level of induced protection against DC3000 in Col-0 than that in the transgenic NahG, the mutant jar1 or etr1, but the protection was absent in the mutant npr1. Therefore, AR156 triggers ISR in Arabidopsis by simultaneously activating the SA- and JA/ET-signaling pathways in an NPR1-dependent manner that leads to an additive effect on the level of induced protection.

Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis

“…It is also known that FB17 specifically induces the expression of PR1 and PDF1.2 in Arabidopsis leaves but not in the roots (Rudrappa et al, 2010). Similarly, B. subtilis strain AR156, when applied to Arabidopsis roots, resulted in the expression of four defense-related genes (PR1, PR2, PR5, and PDF1.2) in the leaves but not in the roots (Niu et al, 2011).…”

“…Because association of Bacillus spp. induces defense response in plants against pathogens, it could be speculated that B. subtilis-derived extracellular components may not elicit defense responses in the root, but may trigger a long-distance signal from the roots to leaves, mediating ISR in the leaves by simultaneously activating the SA-and JA/ET-signaling pathways in an NPR-1-dependent manner (Rudrappa et al, 2010;Niu et al, 2011). Conversely, B. subtilis-derived extracellular components may not play any role in ISR-mediated signaling against foliar pathogens and only involve host suppression for efficient colonization.…”

“…Lipopolysaccharides (LPS), siderophores, or SA from rhizobacteria also are indispensable for successful disease protection (De Meyer et al, 1999; for review, see Ramamoorthy et al, 2001). In connection with ISR and PGPR, Niu et al (2011), reported that Bacillus cereus AR156 induces ISR in Arabidopsis by simultaneously activating SA-and JA/ET-dependent signaling pathways.…”

“…In the same study, it was shown that MAMPs elicit callose deposition on roots and exudation of the antimicrobial compound camalexin. A microarray analysis of the initial phase of colonization by B. subtilis, showed a suppression of root defense-related gene expression (Niu et al, 2011).…”

Characterization of Bacteria Isolated from the Saffron (Crocus sativus L.) Rhizosphere

“…BA6, from the 1-year-old saffron plantation, belongs to B. cereus and is resistant to high salt concentration (Table 1). Some strains of B. cereus are known as PGPRs and can activate pathways of salicylic and jasmonic acids in plants, leading to an improved plant growth and resistance against plant pathogens (Niu et al 2011). BA4, BA3, BA10 and BA18, which were isolated from 2, 10, and 7-years-old plantations respectively, belong to B. megaterium species.…”