Effect of Harpin from Four Pathovars of Pseudomonas syringae on Pea Defense Responses

Abstract

To investigate the role of the proteinaceous elicitor, harpin, on host and nonhost plants, we isolated the harpin-coding gene, hrpZ, from Pseudomonas syringae pvs. pisi, glycinea, tabaci and tomato. Effects of the recombinant harpin proteins on pea plants were analyzed and compared with the effects of the corresponding bacterial treatment. After inoculation of pea with pea pathogen P. syringae pv, p h i , the bacterial population increased and the accumulation of PAL-mRNA and pisatin was inhibited. The nonpathogenic pathovars, glycinea, tabaci and tomato induced both defense responses in pea. However, none of the harpins induced the hypersensitive reaction or accumulation of PAL-mRNA and pisatin in pea. Harpins from P. syringae pvs. glycinea, tomato and p h i did induce these defense responses in tobacco, however, suggesting that externally applied harpins either are not recognized or are nonfunctional in pea plants.The hypersensitive reaction (HR) is one of the most important plant defense responses against avirulent pathogens and/or nonpathogens and is characterized by rapid, localized cell death at the site of pathogen invasion. Many Gram-negative phytopathogenic bacteria elicit the HR in nonhost or resistant plants. Molecular and genetic investigations revealed that hrp genes regulate the hypersensitive zeaction and pathogenicity in several pathovars of Pseudomonas syringae 2 8 5 8 I Q 3 11-13) and other phytopathogenic bacteria, such as X a n t~~~~ campes~ris pathovars, X . oryzae pv. oryzae, Ralstonia solanacearum, Erwinia amybvora, E. chrysanthemi and E. carotovor#". Hrp is known as a gene cluster about 12-25kb long comprising six to eight transcriptional units that encode for 19-26 unique protein products. Sequencing and functional analyses have suggested that Hrp proteins have various functions as components of the type I11 secretion system and regulatory proteins, as well as the proteinaceous HR elicitor, harp~3,~1*-i0,13,14). Harpins are glycine-rich, cysteine-lacking, heat-stable extracellular proteins of ca. 35-kDa having HR-elicitor activity'O).To elucidate the role of harpins in host-parasite interactions, we have recently isolated a hrp cluster from P. syringae pv. pisi 299A (race 1) and the hrpZ gene that encodes the harpin from other races of P. syringae pvs. pki12' , glycinea (race 4), tabaci 6605 and toma~o DC3000 (race 0) using PCR with two primers corresponding to the hrpA and hrpB genes15). Sequencing analysis of the hrpZ gene from race 1 and race 3 of P. syr~ngae pv. pisi revealed that they share a completely identical amino acid sequence, suggesting that harpin is not involved in race-cultivar specificity1z). In this study, we investigated the role of harpins from P. syringae in basic compatibility (species specificity) and the effects of recombinant harpin proteins on the pea defense response.To evaluate host responses after inoculation with four pathovars of P. syringae, we first measured the propagation of each bacterium in inoculated pea leaves (Pisum sativum cv. Midoriusui), Inoculat...

Induced defense responses in tomato against bacterial spot by proteins synthesized by endophytic bacteria

“…Defense responses in plants elicited by macromolecules of proteic nature are usually related to systemic acquired resistance (SAR) (Wei et al, 1992a(Wei et al, , 1995Tanaka et al, 2001). However, Romeiro et al (2005Romeiro et al ( , 2010 showed that there is induced systemic resistance (ISR) in tomato by a protein synthesized by the rhizobacterium Bacillus cereus.…”

“…These studies may encourage research lines that eventually lead to bioproduct development. This was the case with the harpin protein synthesized by bacteria of the genera Erwinia, Ralstonia and Pseudomonas (Wei et al, 1992a(Wei et al, , 1992b(Wei et al, , 1993(Wei et al, , 1995(Wei et al, , 2000Tanaka et al, 2001;Dayan et al, 2009) that generated the commercial products Messenger ® and ProAct ® with broad-spectrum activity against phytopathogens of various crops (Dayan et al, 2009).…”

Degeneration of hrpZ gene in Pseudomonas syringae pv. tabaci to evade tobacco defence: an arms race between tobacco and its bacterial pathogen

“…Similarly, harpin Pss , harpin Pgl and harpin Pto (harpins from Pss , Pgl and Pto , respectively) elicit HR in tomato but not in soybean (Preston et al ., 1995). We also observed that the recombinant harpin Pto , harpin Pgl and harpin Ppi (harpin from Ppi ) did not elicit pea defence responses at a concentration of 6.8 µ m (Tanaka et al ., 2001). Thus, the effects of harpin vary among plant species, and leguminous plants seem to be insensitive or slightly sensitive to harpins from P. syringae .…”