Abstract
Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice bacterial blight, which is a major rice disease in tropical Asian countries. An attempt has been made to investigate gene expression patterns of three Xoo strains on the minimal medium XOM2, PXO99 (P6) and PXO86 (P2) from the Philippines, and GD1358 (C5) from China, which exhibited different virulence in 30 rice varieties, with putative virulence factors using deep sequencing. In total, 4,781 transcripts were identified in this study, and 1,151 and 3,076 genes were differentially expressed when P6 was compared with P2 and with C5, respectively. Our results indicated that Xoo strains from different regions exhibited distinctly different expression patterns of putative virulence-relevant genes. Interestingly, 40 and 44 genes involved in chemotaxis and motility exhibited higher transcript alterations in C5 compared with P6 and P2, respectively. Most other genes associated with virulence, including exopolysaccharide (EPS) synthesis, Hrp genes and type III effectors, including Xanthomonas outer protein (Xop) effectors and transcription activator-like (TAL) effectors, were down-regulated in C5 compared with P6 and P2. The data were confirmed by real-time quantitative RT-PCR, tests of bacterial motility, and enzyme activity analysis of EPS and xylanase. These results highlight the complexity of Xoo and offer new avenues for improving our understanding of Xoo-rice interactions and the evolution of Xoo virulence.
Highlights
The gram-negative plant pathogenic Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of bacterial blight disease on rice [1]
Bacterial blight occurs in most rice-growing areas of the world, and Xoo isolates from within and across Asia, Africa, and Australia show a great diversity of genotypes based on the polymorphisms of transposable elements, predominantly insertion sequences (IS), avirulence genes, rep/box elements, and other markers [57]
A large set of genes associated with the expression of Hrp genes and T3 effectors were significantly up-regulated in P6 and P2
Summary
The gram-negative plant pathogenic Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of bacterial blight disease on rice [1]. The complete genome sequences have been published for Japanese race 1 [3], Korean race 1 [4], and PXO99A, a 5-azacytidine-resistant derivative of the Philippines’ race 6 [5] These genomes have helped to elucidate the molecular interactions between a pathogen and a monocotyledonous plant and have greatly advanced the understanding of the molecular interactions between rice and Xoo. Several virulencerelated factors have been identified, such as the hypersensitive response and pathogenicity (hrp) genes [6], type III (T3) effectors [7,8], genes associated with the production of exopolysaccharides (EPS), and genes associated with motility and extracellular enzymes [9,10]. The T3S system is transcriptionally induced in certain minimal media and in plants [12], and the ompR-type response regulator HrpG, which is activated by unknown plant signals, controls the genome-wide regulon, including hrps, T3 effectors and putative virulence genes [13]
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