Rhizobacterial salicylate production provokes headaches!

Abstract

Background Salicylic acid (SA) is produced in significant amounts by certain plant growth promoting rhizosphere bacteria, and some of these rhizobacteria have the ability to induce systemic resistance against diseases in plants. Exogenous application of SA to plants has long been known to lead to protection against a range of plant pathogens through the elicitation of systemic acquired resistance. Thus, it is reasonable to assume that the SA producing plant beneficial rhizobacteria elicit induced resistance through the production of SA. Scope and conclusions However, we discuss here that bacterial secretion of SA in vitro appears to be an artifact and that the bacteria will normally incorporate SA into SA-containing metabolites, mainly SA-based siderophores, under environmental conditions. Therefore, we argue that rhizobacteria do not likely excrete free SA into the rhizosphere thereby not inducing resistance in plants through this metabolite. SA detected in the rhizosphere is most likely produced by the plant and we discuss the impact of this phenolic compound on microbial interactions.

Endophytic colonization and biocontrol performance of Pseudomonas fluorescens PICF7 in olive (Olea europaea L.) are determined neither by pyoverdine production nor swimming motility

“…Besides, disease suppression mediated by siderophores has been shown to play an important role in some cases (Buysens et al, 1996;Audenaert et al, 2002), but minor (or no involvement at all) in others (Hamdan et al, 1991;Ongena et al, 1999;Djavaheri et al, 2012). Some Pseudomonas-produced siderophores have also been suggested to suppress plant diseases via induction of systemic resistance, although this issue is also controversial (Djavaheri et al, 2012;Bakker et al, 2014). Pseudomonas fluorescens PICF7 produces Pvd (Mercado-Blanco et al, 2004; this study), although production of additional, secondary siderophore(s) cannot be completely ruled out according to PICF7 genome data (Martínez et al, unpublished).…”

“…may synthesize a wide diversity of siderophores, iron (Fe 3+ )-chelating compounds frequently related with the biocontrol activity exerted by many strains of this genus (Mercado-Blanco and Bakker, 2007). Nevertheless, the true implication of Pseudomonas-produced siderophores in biological control of soil-borne pathogens is a controversial issue (Cornelis and Matthijs, 2002;Weller, 2007;Lemanceau et al, 2009;Bakker et al, 2014).…”

Molecular networks in plant–pathogen holobiont

“…Disruption of aldA and aldB , encoding IAA biosynthesis enzymes, leads to reduced bacterial virulence in the plant host in an SA‐dependent manner , suggesting that hijacking auxin signaling is a virulence mechanism that suppresses SA‐mediated immunity. Notably, some bacteria are known to produce SA although the physiological significance of this during interaction with plants remains elusive .…”

“…Bacteria produce a variety of phytohormones (mimics), such as IAA, SA, ET, ABA, cytokinin, gibberellin, and COR ; some of these phytohormones (mimics) produced by bacteria have been shown to affect plant physiology including plant immunity . On the other hand, bacteria also use phytohormones to regulate their own responses.…”

Molecular Patterns of Rhizobacteria Involved in Plant Immunity Elicitation

“…In summary, a clear role for PGPR-produced SA in ISR has not been clearly established and appeared to depend on the pathosystem considered. Moreover, SA production in the rhizosphere by these bacteria is not obvious as the compound is better channelled in the synthesis of other bioactive siderophores (Bakker, Ran, & Mercado-Blanco, 2014).…”