Differentially-expressed genes in rice infected by Xanthomonas oryzae pv. oryzae relative to a flagellin-deficient mutant reveal potential functions of flagellin in host–pathogen interactions

Chao Yu,Chenyang He,Fang Tian,Jan E Leach,Huamin Chen

doi:10.1186/s12284-014-0020-7

Abstract

BackgroundPlants have evolved a sensitive defense response system that detects and recognizes various pathogen-associated molecular patterns (PAMPs) (e.g. flagellin) and induces immune responses to protect against invasion. Transcriptional responses in rice to PAMPs produced by Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen, have not yet been defined.ResultsWe characterized transcriptomic responses in rice inoculated with the wildtype (WT) Xoo and flagellin-deficient mutant ∆fliC through RNA-seq analysis. Digital gene expression (DGE) analysis based on Solexa/Illumina sequencing was used to investigate transcriptomic responses in 30 day-old seedlings of rice (Oryza sativa L. cv. Nipponbare). 1,680 genes were differentially-expressed (DEGs) in rice inoculated with WT relative to ∆fliC; among which 1,159 genes were up-regulated and 521 were down-regulated. Expression patterns of 12 randomly-selected DEGs assayed by quantitative real time PCR (qRT-PCR) were similar to those detected by DGE analyses, confirming reliability of the DGE data. Functional annotations revealed the up-regulated DEGs are involved in the cell wall, lipid and secondary metabolism, defense response and hormone signaling, whereas the down-regulated ones are associated with photosynthesis. Moreover, 57 and 21 specifically expressed genes were found after WT and ∆fliC treatments, respectively.ConclusionsDEGs were identified in rice inoculated with WT Xoo relative to ∆fliC. These genes were predicted to function in multiple biological processes, including the defense response and photosynthesis in rice. This study provided additional insights into molecular basis of rice response to bacterial infection and revealed potential functions of bacterial flagellin in the rice-Xoo interactions.

Highlights

Plants have evolved a sensitive defense response system that detects and recognizes various pathogen-associated molecular patterns (PAMPs) and induces immune responses to protect against invasion
Digital gene expression (DGE) sequencing in rice leaves inoculated with WT Xanthomonas oryzae pv. oryzae (Xoo) or ΔfliC For DGE sequencing, RNAs from rice leaves inoculated with the WT or ΔfliC mutant were extracted to prepare two cDNA libraries for RNA-seq analysis
Acidovorax avenae induced hypersensitive cell death in cultured rice cells (Che et al 2000); the specificity of this induction of immune responses was attributed to flagellin glycosylation (Taguchi et al 2010; Hirai et al 2011), and suggested that the function of bacterial flagellin in Pattern-triggered immunity (PTI) in rice relied on its origin and post-translational modification

Summary

Introduction

Plants have evolved a sensitive defense response system that detects and recognizes various pathogen-associated molecular patterns (PAMPs) (e.g. flagellin) and induces immune responses to protect against invasion. Plants developed resistance (R) proteins to recognize effectors, leading to activation of effectortriggered immunity (ETI) (Jones and Dangl 2006). FLAGELLIN SENSITIVE2 (FLS2), the receptor that recognizes flagellin in A. thaliana, shares structural and functional homologies with known plant resistance proteins (Gomez-Gomez and Boller 2000). Flagellin and flg are recognized and bound to the extracelluar domain of FLS2 This induces FLS2 heteromerization with BRASSINOSTEROID INSENSITIVE 1-associate kinase 1 (BAK1) and activates signaling cascades that culminate in the induction of defense responses (Heese et al 2007; Ali and Reddy 2008; Sun et al 2013). OsFLS2, the ortholog of FLS2 in rice, mediates immune responses induced by flagellin (Takai et al 2008)

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