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“Background Pseudomonas chlororaphis strain PA23 is a Alpelisib concentration biocontrol agent able to protect canola from stem rot disease caused by the fungus

Sclerotinia sclerotiorum (Lib.) de Bary [1, 2]. This bacterium produces a number of compounds including phenazine 1-carboxylic acid (PCA), 2-hydroxyphenazine (2-OH-PHZ), pyrrolnitrin, protease, lipase, chitinase and siderophores, some of which have been shown to contribute Cediranib (AZD2171) to fungal antagonism [3–5]. Public concern

over the use of chemical pesticides together with the potential for acquiring resistance to these compounds has led to renewed interest in bacterial antagonists, such as PA23, for biocontrol. Despite demonstrating excellent disease control in the greenhouse, many biocontrol agents suffer from inconsistent performance in the field [6–8]. Poor field performance is likely due, at least in part, to variable expression of genes and gene products required for disease suppression. It is essential, therefore, to elucidate the molecular mechanisms mediating PA23 biocontrol so that production of the pathogen-suppressing factor(s) can be optimized in the environment. In Pseudomonas spp. that act as biocontrol agents, expression of disease-suppressive metabolites is controlled by a multi-tiered network of regulation. One of the key regulatory elements is the GacS/GacA two-component signal transduction system, comprised of the sensor kinase GacS and its cognate response regulator GacA [9]. In many pseudomonads, including PA23, a mutation in gacS or gacA leads to a loss of fungal antagonism [4, 9]. Working in concert with GacS/GacA is the Rsm system which consists of RsmA-like repressor proteins and untranslated regulatory RNAs. The repressor proteins act post-transcriptionally by binding to the ribosome-binding site (RBS) in target mRNA [10].