Abstract
BackgroundXanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight, a devastating rice disease. The Xoo-rice interaction, wherein wide ranging host- and pathogen-derived proteins and genes wage molecular arms race, is a research hotspot. Hence, the identification of novel rice-induced Xoo virulence factors and characterization of their roles affecting rice global gene expression profiles will provide an integrated and better understanding of Xoo-rice interactions from the molecular perspective.ResultsUsing comparative proteomics and an in vitro interaction system, we revealed that 5 protein spots from Xoo exhibited significantly different expression patterns (|fold change| > 1.5) at 3, 6, 12 h after susceptible rice leaf extract (RLX) treatment. MALDI-TOF MS analysis and pathogenicity tests showed that 4 host-induced proteins, including phosphohexose mutase, inositol monophosphatase, arginase and septum site-determining protein, affected Xoo virulence. Among them, mutants of two host-induced carbohydrate metabolism enzyme-encoding genes, ΔxanA and Δimp, elicited enhanced defense responses and nearly abolished Xoo virulence in rice. To decipher rice differentially expressed genes (DEGs) associated with xanA and imp, transcriptomic responses of ΔxanA-treated and Δimp-treated susceptible rice were compared to those in rice treated with PXO99A at 1 and 3 dpi. A total of 1521 and 227 DEGs were identified for PXO99A vs Δimp at 1 and 3 dpi, while for PXO99A vs ΔxanA, there were 131 and 106 DEGs, respectively. GO, KEGG and MapMan analyses revealed that the DEGs for PXO99A vs Δimp were mainly involved in photosynthesis, signal transduction, transcription, oxidation-reduction, hydrogen peroxide catabolism, ion transport, phenylpropanoid biosynthesis and metabolism of carbohydrates, lipids, amino acids, secondary metabolites, hormones, and nucleotides, while the DEGs from PXO99A vs ΔxanA were predominantly associated with photosynthesis, signal transduction, oxidation-reduction, phenylpropanoid biosynthesis, cytochrome P450 and metabolism of carbohydrates, lipids, amino acids, secondary metabolites and hormones. Although most pathways were associated with both the Δimp and ΔxanA treatments, the underlying genes were not the same.ConclusionOur study identified two novel host-induced virulence factors XanA and Imp in Xoo, and revealed their roles in global gene expression in susceptible rice. These results provide valuable insights into the molecular mechanisms of pathogen infection strategies and plant immunity.
Highlights
Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight, a devastating rice disease
Identification of Host-Induced Proteins of X. oryzae pv. oryzae PXO99A in the In Vitro Assay System Using IR24 rice leaf extract (RLX) To identify proteins of X. oryzae pv. oryzae PXO99A that were up- or downregulated during its interaction with host rice IR24, an in vitro assay system combined with two-dimensional gel analysis was used to compare the total protein expression profiles from RLX-treated and untreated Xoo cells
In this study, comparative proteomics analysis and pathogenicity tests revealed that 4 pathogenic-related proteins (XanA, inositol monophosphatase (Imp), RocF and MinD) of Xoo were continuously induced by host rice at 3, 6, and 12 h in an in vitro interaction system
Summary
Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight, a devastating rice disease. The response of pathogens to plant defenses is complex and sophisticated, involving a battery of biological and physiological processes, represented by secretion of effectors, activation of virulence factors, modification of host gene expression and evolution of pathogenic strategies to evade host immune attacks (Ryan et al 2011, Morris et al 2017). Oryzae (Xoo), the causative agent of bacterial blight of rice, is one of the model organisms for studying the molecular mechanisms of plantbacterium interactions and causes serious reductions in rice yields worldwide. Several host-induced genes/proteins involved in plant-bacterium interactions have been revealed by a variety of comparative transcriptomic and proteomic studies in vivo and in vitro. It was observed in Xoo that the expression of genes related to ion transport, chemotaxis and pathogenicity could be induced upon initial interactions with rice leaf extract (RLX) (Kim et al 2016). The functions of host-induced proteins or genes in the Xoo-rice interaction have rarely been studied
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