Flagellin Glycosylation Island in Pseudomonas syringae pv. glycinea and Its Role in Host Specificity

Abstract

The deduced amino acid sequences of the flagellins of Pseudomonas syringae pv. tabaci and P. syringae pv. glycinea are identical; however, their abilities to induce a hypersensitive reaction are clearly different. The reason for the difference seems to depend on the posttranslational modification of the flagellins. To investigate the role of this posttranslational modification in the interactions between plants and bacterial pathogens, we isolated genes that are potentially involved in the posttranslational modification of flagellin in P. syringae pv. glycinea (glycosylation island); then defective mutants with mutations in these genes were generated. There are three open reading frames in the glycosylation island, designated orf1, orf2, and orf3. orf1 and orf2 encode putative glycosyltransferases, and mutants with defects in these open reading frames, ⌬orf1 and ⌬orf2, secreted nonglycosylated and slightly glycosylated flagellins, respectively. Inoculation tests performed with these mutants and original nonhost tobacco leaves revealed that ⌬orf1 and ⌬orf2 could grow on tobacco leaves and caused symptom-like changes. In contrast, these mutants failed to cause symptoms on original host soybean leaves. These data indicate that putative glycosyltransferases encoded in the flagellin glycosylation island are strongly involved in recognition by plants and could be the specific determinants of compatibility between phytopathogenic bacteria and plant species.Flagellin is an essential component of the flagellum filament of bacteria. In recent years, there has been increasing evidence that flagellin is posttranslationally glycosylated (4, 20). However, workers have just started to elucidate the molecular basis of this modification. Thus, little is known about its biological significance.The isolates of the phytopathogenic bacterium Pseudomonas syringae can be classified into more than 50 pathovars on the basis of virulence for host plant species. In a previous study, P. syringae flagellin was found to elicit hypersensitive reactions (HR) in nonhost plants (27). Several studies to characterize elicitor flagellins have been performed with Pseudomonas avenae (Acidovorax avenae) (5) and P. syringae pv. tabaci (7). These flagellins have been reported to induce plant defense responses in cultured cells of rice (5), tomato, and Arabidopsis thaliana (7). A 22-amino-acid peptide (flg22) of a conserved domain near the N terminus based on the sequence of Pseudomonas aeruginosa flagellin has been reported to induce plant defense responses but not hypersensitive cell death (7). Thus, flg22 is known as a general elicitor of an innate immune response in plants (10). However, flagellins from P. avenae (5) and flagellins from P. syringae pv. glycinea and P. syringae pv. tomato (27) are known to induce plant cell death in nonhost rice and tobacco plants, respectively. These results indicate that the flagellin proteins have roles both as nonspecific elicitors of general defense responses and as specific elicitors of HR cell death in defined ...

Comparative phylogenomics of the food-borne pathogen Campylobacter jejuni reveals genetic markers predictive of infection source

“…Variant flagellin glycoforms have been shown to be expressed in different hosts or environments in the opportunistic pathogen P. aeruginosa that may provide the pathogen with a specific survival advantage (25). Recently, flagellin glycosylation in the plant pathogen Pseudomonas syringae has been shown to be involved in determining plant host specificity (26). We hypothesize that those genes cj1321-cj1326 encode a distinct flagellin glycoform specifically maintained in livestock isolates, which could involve improved adhesion to the host cells, improved survival within livestock gut, and͞or stimulation (or evasion) of the immune system.…”

A Homologue of the 3-Oxoacyl-(Acyl Carrier Protein) Synthase III Gene Located in the Glycosylation Island of Pseudomonas syringae pv. tabaci Regulates Virulence Factors via N -Acyl Homoserine Lactone and Fatty Acid Synthesis

“…Because the proteins encoded by orf1 and orf2 showed homology to a putative glycosyltransferase and the molecular mass of the flagellin of each orf1 and orf2 deletion mutant (⌬orf1 and ⌬orf2 mutants) was decreased, these genes are thought to encode the glycosyltransferases. Inoculation of these mutants into each host plant confirmed that glycosylation of flagellin proteins plays an important role in their virulence (33,36). While the ⌬orf3 mutants of P. syringae pv.…”

“…glycinea does induce HR on tobacco plants, suggesting that posttranslational modification of flagellin determines the specificity to induce HR (34). We recently reported that genes existing upstream of fliC, which encodes flagellin protein, are involved in the glycosylation of flagellin in these two pathovars (33,36). There are three open reading frames, namely, orf1, orf2, and orf3, in the glycosylation islands of P. syringae pv.…”

“…A homology search revealed that orf3 is highly homologous to the putative 3-oxoacyl-(acyl carrier protein [ACP]) synthase III (␤-ketoacyl-ACP synthase III) genes of Escherichia coli, Salmonella enterica serovar Typhimurium, and Pseudomonas putida strain KT2440 (24,36). It has been reported that a 3-oxoacyl-ACP synthase III called FabH is one of the enzymes in the type II fatty acid synthesis system (20).…”

The syntaxin SYP132 contributes to plant resistance against bacteria and secretion of pathogenesis-related protein 1

“…As in mammals, recognition of pathogen-associated molecular patterns (PAMPs) such as bacterial flagellin forms the basis of basal resistance and is thought to provide protection from the majority of potential bacterial invaders (1)(2)(3)(4)(5)(6). By contrast, ''race-specific'' responses may be a second line of defense triggered by the recognition of avirulence (Avr) gene products, or effector proteins, injected into the host by the bacterium via a type III secretion system (7)(8)(9).…”