Comparative analysis of defence responses induced by the endophytic plant growth-promoting rhizobacterium Burkholderia phytofirmans strain PsJN and the non-host bacterium Pseudomonas syringae pv. pisi in grapevine cell suspensions

Abstract

Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms that colonize the rhizosphere of many plant species and confer beneficial effects, such as an increase in plant growth. PGPR are also well known as inducers of systemic resistance to pathogens in plants. However, the molecular mechanisms involved locally after direct perception of these bacteria by plant cells still remain largely unknown. Burkholderia phytofirmans strain PsJN is an endophytic PGPR that colonizes grapevine and protects the plant against the grey mould disease caused by Botrytis cinerea. This report focuses on local defence events induced by B. phytofirmans PsJN after perception by the grapevine cells. It is demonstrated that, after addition to cell suspension cultures, the bacteria were tightly attaching to plant cells in a way similar to the grapevine non-host bacteria Pseudomonas syringae pv. pisi. B. phytofirmans PsJN perception led to a transient and monophasic extracellular alkalinization but no accumulation of reactive oxygen species or cell death were detected. By contrast, challenge with P. syringae pv. pisi induced a sustained and biphasic extracellular alkalinization, a two phases oxidative burst, and a HR-like response. Perception of the PGPR also led to the production of salicylic acid (SA) and the expression of a battery of defence genes that was, however, weaker in intensity compared with defence gene expression triggered by the non-host bacteria. Some defence genes up-regulated after B. phytofirmans PsJN challenge are specifically induced by exogenous treatment with SA or jasmonic acid, suggesting that both signalling pathways are activated by the PGPR in grapevine.

Grapevine colonization by endophytic bacteria shifts secondary metabolism and suggests activation of defense pathways

“…Experimental evidence suggests that plant colonization by particular bacterial endophytes is marked by a change in the expression of key genes of plant central metabolic pathways (Bordiec et al 2011). This is supported by observations showing that endophytic bacteria of the genus Paenibacillus generate a metabolic signature (a recurrent change in the metabolic profile of plants after inoculation with the same strain in repeated experiments) when artifically inoculated in poplar plants (Scherling et al 2009).…”

Roots Shaping Their Microbiome: Global Hotspots for Microbial Activity

“…Contradictory studies showed that in the rice-Azoarcus system, flagella are required for efficient colonization rather than act as MAMPs (21). The so-far limited studies suggest that endophytes induce only low levels of defense responses in compatible interactions (71), mostly from the JA pathway (1, 71), and they might even trigger specialized signaling cascades, but the mechanisms are still obscure (17,26,85). Future work should integrate approaches using plant mutants in addition to functional genomic analyses of the bacterial factors in reductionist systems; however, microbial community studies may give insights as well (see below).…”

Paraburkholderia phytofirmans PsJN-Plants Interaction: From Perception to the Induced Mechanisms

“…Plant perception of endophytic strain PsJN begins after an exposure to bacterial signals such as flagellin leading to the plant response characterized by early and long-term responses in plant immunity and plant growth regulation and morphogenesis (Bordiec et al, 2011; Trdá et al, 2013). It has been shown that P. phytofirmans PsJN is perceived by grapevine cell suspensions and led to the production of a monophasic and transient burst of alkalinization during the first minute of the interaction (Bordiec et al, 2011).…”