The biocontrol agent Pseudomonas chlororaphis PA23 primes Brassica napus defenses through distinct gene networks

Abstract

BackgroundThe biological control agent Pseudomonas chlororaphis PA23 is capable of protecting Brassica napus (canola) from the necrotrophic fungus Sclerotinia sclerotiorum via direct antagonism. While we have elucidated bacterial genes and gene products responsible biocontrol, little is known about how the host plant responds to bacterial priming on the leaf surface, including global changes in gene activity in the presence and absence of S. sclerotiorum.ResultsApplication of PA23 to the aerial surfaces of canola plants reduced the number of S. sclerotiorum lesion-forming petals by 91.1%. RNA sequencing of the host pathogen interface showed that pretreatment with PA23 reduced the number of genes upregulated in response to S. sclerotiorum by 16-fold. By itself, PA23 activated unique defense networks indicative of defense priming. Genes encoding MAMP-triggered immunity receptors detecting flagellin and peptidoglycan were downregulated in PA23 only-treated plants, consistent with post-stimulus desensitization. Downstream, we observed reactive oxygen species (ROS) production involving low levels of H2O2 and overexpression of genes associated with glycerol-3-phosphate (G3P)-mediated systemic acquired resistance (SAR). Leaf chloroplasts exhibited increased thylakoid membrane structures and chlorophyll content, while lipid metabolic processes were upregulated.ConclusionIn addition to directly antagonizing S. sclerotiorum, PA23 primes the plant defense response through induction of unique local and systemic defense networks. This study provides novel insight into the effects of biocontrol agents applied to the plant phyllosphere. Understanding these interactions will aid in the development of biocontrol systems as an alternative to chemical pesticides for protection of important crop systems.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3848-6) contains supplementary material, which is available to authorized users.

Insights into plant-beneficial traits of probiotic Pseudomonas chlororaphis isolates

“…In addition to direct growth antagonism of microbes, the phenazines also induce systemic resistance in plants such that protection against shoot pathogens is triggered by root colonization with P. chlororaphis isolates. Both PCN-and PCA/2-OH PHZ-producing microbes possess this ability [23][24][25]. Duke et al [23] observed that aerial application of isolates induces both localized and systemic responses associated with resistance.…”

“…Both PCN-and PCA/2-OH PHZ-producing microbes possess this ability [23][24][25]. Duke et al [23] observed that aerial application of isolates induces both localized and systemic responses associated with resistance. Thus, the direct microbial antagonism caused by phenazine production is reinforced by the phenazinemediated upregulation of plant defence mechanisms.…”

Global RNA sequencing reveals enhanced photosynthetic activity and auxin response inBrassica napustreated withPseudomonas chlororaphisPA23

“…chlororaphis, can function as biocontrol agents to directly inhibit the growth of fungal, bacterial, and eukaryotic pathogens through the action of secreted compounds [12][13][14][15][16]. P. chlororaphis strain PA23, a microbe originally isolated from the soybean rhizosphere, is a potent biocontrol agent against fungal pathogens and parasitic nematodes [17,18].…”

Characterization of Rhodopseudomonas palustris population dynamics on tobacco phyllosphere and induction of plant resistance to Tobacco mosaic virus

“…Phyllosphere, also known as aerial part of plant, is the first-line plants used to fight against pathogen infections (Berg, 2009;Natacha et al, 2014). Phyllosphere also provides an ideal habitat for bacterial species that are beneficial to plant growth and stress tolerance (Vorholt, 2012;Kembel et al, 2014;Duke et al, 2017). Successful applications of microbes with biocontrol activities to plant phyllosphere are crucial for effective crop disease managements (Kim et al, 2011;Lambais et al, 2014).…”