Abstract
BackgroundMicrobe-associated molecular patterns, such as those present in bacterial flagellin, are powerful inducers of the innate immune response in plants. Successful pathogens deliver virulence proteins, termed effectors, into the plant cell where they can interfere with the immune response and promote disease. Engineering the plant immune system to enhance disease resistance requires a thorough understanding of its components.ResultsWe describe a high-throughput screen, using RNA sequencing and virus-induced gene silencing, to identify tomato genes whose expression is enhanced by the flagellin microbe-associated molecular pattern flgII-28, but reduced by activities of the Pseudomonas syringae pv. tomato (Pst) type III effectors AvrPto and AvrPtoB. Gene ontology terms for this category of Flagellin-induced repressed by effectors (FIRE) genes showed enrichment for genes encoding certain subfamilies of protein kinases and transcription factors. At least 25 of the FIRE genes have been implicated previously in plant immunity. Of the 92 protein kinase-encoding FIRE genes, 33 were subjected to virus-induced gene silencing and their involvement in pattern-triggered immunity was tested with a leaf-based assay. Silencing of one FIRE gene, which encodes the cell wall-associated kinase SlWAK1, compromised the plant immune response resulting in increased growth of Pst and enhanced disease symptoms.ConclusionsOur transcriptomic approach identifies FIRE genes that represent a pathogen-defined core set of immune-related genes. The analysis of this set of candidate genes led to the discovery of a cell wall-associated kinase that participates in plant defense. The FIRE genes will be useful for further elucidation of the plant immune system.
Highlights
Microbe-associated molecular patterns, such as those present in bacterial flagellin, are powerful inducers of the innate immune response in plants
We focused on flgII-28 because it has recently emerged as a second Microbe-associated molecular pattern (MAMP) derived from flagellin, in addition to flg22, which is perceived by solanaceous species [12,13]
Using Pseudomonas fluorescens, Pseudomonas putida and flgII28 we investigated pattern-triggered immunity (PTI)-associated transcriptional changes, while Agrobacterium tumefaciens and Pseudomonas syringae pv. tomato (Pst) strain DC3000ΔhrcQ-UΔfliC were chosen to examine the effects due to MAMPs other than flagellin
Summary
Microbe-associated molecular patterns, such as those present in bacterial flagellin, are powerful inducers of the innate immune response in plants. The activation of pattern-triggered immunity (PTI) by MAMPs and DAMPs leads to changes in the intracellular calcium concentration, production of reactive oxygen species, activation of mitogen-activated protein kinase (MAPK) cascades and transcriptional reprogramming [4]. These events lead, in a largely unknown manner, to inhibition of pathogen growth and suppression of disease. Successful pathogens deliver virulence proteins (effectors) into the plant cell and a majority of these proteins appear to function by interfering with host immunity-associated events triggered by MAMP recognition [5]. A second plant defense response, effector-triggered immunity (ETI), can be activated in cases where a specific pathogen effector or its activity is recognized by a host nucleotide-binding leucinerich repeat-containing (NB-LRR) resistance protein [1]
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