Evidence for HrpXo-Dependent Expression of Type II Secretory Proteins in Xanthomonas oryzae pv. oryzae

Abstract

Xanthomonas oryzae pv. oryzae is a causal agent of bacterial leaf blight of rice. Recently, an efficient hrp-inducing medium, XOM2, was established for this bacterium. In this medium, more than 10 proteins were secreted from the wild-type strain of X. oryzae pv. oryzae. Many of these proteins disappeared or decreased in amount in culture on XOM2 when incubated with the strain that has a mutation in the hrp regulatory gene. Interestingly, the secretory protein profile of a mutant lacking a type III secretion system (TTSS), components of which are encoded by hrp genes, was similar to that of the wild-type strain except that a few proteins had disappeared. This finding suggests that many HrpXo-dependent secretory proteins are secreted via systems other than the TTSS. By isolating mutant strains lacking a type II secretion system, we examined this hypothesis. As expected, many of the HrpXo-dependent secretory proteins disappeared or decreased when the mutant was cultured in XOM2. By determining the N-terminal amino acid sequence, we identified one of the type II secretory proteins as a cysteine protease homolog, CysP2. Nucleotide sequence analysis revealed that cysP2 has an imperfect plant-inducible-promoter box, a consensus sequence which HrpXo regulons possess in the promoter region, and a deduced signal peptide sequence at the N terminus. By reverse transcription-PCR analysis and examination of the expression of CysP2 by using a plasmid harboring a cysP2::gus fusion gene, HrpXo-dependent expression of CysP2 was confirmed. Here, we reveal that the hrp regulatory gene hrpXo is also involved in the expression of not only hrp genes and type III secretory proteins but also some type II secretory proteins.In general, plant-pathogenic bacteria possess hypersensitive response and pathogenicity (hrp) genes, which are clustered in their chromosomes. hrp genes encode a type III secretion system (TTSS) that delivers virulence and avirulence factors from the bacteria to plant cells and are required for pathogenesis in host plants and for triggering a hypersensitive response in nonhost plants (1,38). Transcriptional regulation of hrp genes depends on environmental conditions. The expression of hrp genes is generally suppressed in complex media and induced in planta and under certain in vitro conditions (6,24,35,39).In xanthomonads, the hrp cluster comprises six hrp loci, hrpA to hrpF, which are all required for full pathogenicity, and their expression is regulated by two genes, hrpX and hrpG, which are located outside the hrp gene cluster region (7, 36). The HrpG protein belongs to the OmpR family of two-component regulatory systems and activates the expression of hrpA and hrpX (37). HrpX, an AraC-type transcriptional activator, has been reported to control the expression of the operons hrpB to hrpF, which contain the hrp genes encoding a component of TTSS (36). It has also been suggested that HrpX controls some effector proteins (5). Several genes that are regulated in a HrpX-dependent manner possess the consensus nucleotide ...

Candida albicansCell Wall Proteins

“…Multiple export pathways in various bacteria have been established, including a type III (114,285,310), a type IV (82), and the twin-arginine translocation (Tat) (81) pathways. However, there are still proteins, including those mentioned above, that are secreted by an unidentified route(s) and lack anchorage structures in the bacterial cell wall (21, 57).…”

Expressional Regulation of the Virulence Gene eglXoA Encoding Endoglucanase, Dependent on HrpXo and Cyclic AMP Receptor-Like Protein (Clp) in Xanthomonas oryzae pv. oryza

“…citri [29] and extracellular proteases in Xcc [21]. In Xoo, only a gene encoding the extracellular T2SS enzyme Cysp2, which is related to pathogenicity, has so far been demonstrated to be regulated by HrpX [19]. These reports support that HrpX is also involved in regulating the expression of some T2SS-related extracellular enzymes.…”

Recombinant expression and characterization of a cysteine peptidase from Xanthomonas citri subsp citri

“…Yamazaki et al (2008) have suggested the presence of an imperfect PIP box for the CPXAC gene. By contrast, pathogenicity genes hrpX and hrpG are responsible for the secretion of proteins in type III and some type II systems (Sandkvist, 2001;Furutani et al, 2004). Furthermore, a functional interplay between both secretion systems has been suggested (Büttner and Bonas, 2010).…”

“…This high degree of similarity was expected, as both organisms belong to the family Xanthomonadaceae. The sequence of cysteine peptidase from Xac is also similar to that of Pseudomonas syringae (76% similarity), which causes leaf spot disease on tomato plants (Hirano and Upper, 2000); a cysteine peptidase from the bacterium Xylella fastidiosa (72% similarity), which is responsible for citrus variegated chlorosis ; and to a cysteine peptidase from X. oryzae (70% similarity), which is the causal agent of bacterial leaf blight in rice (Furutani et al, 2004). With the exception of the sequence from X. fastidiosa, which has been studied by Nogaroto et al (2006), the translation initiation sites of all sequences used in the alignment of Figure 1 were verified only with genome annotation.…”