A Harpin Binding Site in Tobacco Plasma Membranes Mediates Activation of the Pathogenesis-Related Gene HIN1 Independent of Extracellular Calcium but Dependent on Mitogen-Activated Protein Kinase Activity

Abstract

Harpin from the bean halo-blight pathogen Pseudomonas syringae pv phaseolicola (harpin Psph ) elicits the hypersensitive response and the accumulation of pathogenesis-related gene transcripts in the nonhost plant tobacco. Here, we report the characterization of a nonproteinaceous binding site for harpin Psph in tobacco plasma membranes, which is assumed to mediate the activation of plant defense responses in a receptor-like manner. Binding of 125 I-harpin Psph to tobacco microsomal membranes (dissociation constant ‫؍‬ 425 nM) and protoplasts (dissociation constant ‫؍‬ 380 nM) was specific, reversible, and saturable. A close correlation was found between the abilities of harpin Psph fragments to elicit the transcript accumulation of the pathogenesis-related tobacco gene HIN1 and to compete for binding of 125 Iharpin Psph to its binding site. Another elicitor of the hypersensitive response and HIN1 induction in tobacco, the Phytophthora megasperma -derived ␤ -elicitin ␤ -megaspermin, failed to bind to the putative harpin Psph receptor. In contrast to activation by ␤ -megaspermin, harpin Psph -induced activation of the 48-kD salicylic acid-responsive mitogen-activated protein kinase (MAPK) and HIN1 transcript accumulation were independent of extracellular calcium. Moreover, use of the MAPK kinase inhibitor U0126 revealed that MAPK activity was essential for pathogenesis-related gene expression in harpin Psph -treated tobacco cells. Thus, a receptor-mediated MAPK-dependent signaling pathway may mediate the activation of plant defense responses induced by harpin Psph .

Dynamic Changes in the Localization of MAPK Cascade Components Controlling Pathogenesis-related (PR) Gene Expression during Innate Immunity in Parsley

“…Perhaps the most intriguing analogous system for our observations is the growth factor-induced nuclear translocation of the ERK1/2 MAPKs from mammals. Sequence analysis alone demonstrates that the plant MAPKs described in this work bear strong similarity to mammalian ERK1/2, so much so that anti-active ERK1/2 antibodies can be commonly employed to study the activity of plant MAPKs (16,53,54). This must suggest a common ancestry for the plant MAPKs typified by PcMPK6, 3a, and 3b in this study and mammalian MAPKs typified by ERK1/2.…”

“…The Pseudomonas syringae HrpZ protein is a bacterial elicitor of plant defense reactions (53) and has previously been shown to activate the parsley orthologues of MPK6 and MPK3 (16), via a mechanism that is independent of the Pep-13 receptor. 2 The immunoprecipitates from control or elicited cells were subjected to in vitro kinase phosphorylation assays using either PcMPK6-kr (for PcMKK5) or MBP (for PcMPK6) as substrate.…”

Pleiotropic effect of the insertion of the Agrobacterium rhizogenes rolD gene in tomato (Lycopersicon esculentum Mill.)

“…SIPK is also induced by pathogens and elicitors, and is involved in the activation of defense-related genes (Zhang and Klessig 1997;Zhang et al 1998). A relationship between protein kinasemediated signal transduction in the defense response and the activation of pathogenesis-related gene expression has been clearly established in several instances (Lee et al 2001;Murillo et al 2001); therefore it is tempting to speculate that in the transgenic plants the increase in proline content due to the presence of rolD could induce SIPK, starting a signal transduction cascade whose final outcome was PR-1 gene expression.…”

Mitogen-activated Protein Kinases Play an Essential Role in Oxidative Burst-independent Expression of Pathogenesis-related Genes in Parsley

“…In all systems whereby MAPK activity has been studied with respect to elicitor responses, activation of members of the AtMPK6 subgroup has been described (1,27). This includes the responses of tobacco SIPK to general elicitors, such as Harpin and elicitins, TMV infection, and race-specific elicitation (32)(33)(34)(35)(36); alfalfa SIMK to chitin, ergosterol, and ␤-glucans (37); A. thaliana AtMPK6 to bacterial elicitors including the flg22 peptide from flagellin (38) and Harpin (39). It was recently demonstrated for A. thaliana that MAPKs can also act as negative regulators of defense responses, as shown for AtMPK4 mutants (40); however, this would appear to be contradictory to the activation of this kinase described in response to Harpin (39).…”