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First published online July 15, 2005; 10.1104/pp.105.063032 Plant Physiology 138:2406-2416 (2005) © 2005 American Society of Plant Biologists Rapid Phosphorylation of a Syntaxin during the Avr9/Cf-9-Race-Specific Signaling Pathway1Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, United Kingdom
The tomato (Lycopersicon esculentum) resistance (R) gene Cf-9 is required for resistance to races of the fungal pathogen Cladosporium fulvum expressing the elicitor Avr9 and also confers responsiveness to Avr9 in Cf-9-containing transgenic tobacco (Nicotiana tabacum; Cf9 tobacco). Although protein phosphorylation is required for many early Avr9/Cf-9-signaling events, so far the only phosphorylation targets known in this race-specific signaling pathway are three kinases: the two mitogen-activated protein kinases, wound-induced protein kinase and salicylic acid-induced protein kinase, and the calcium-dependent protein kinase NtCDPK2. Here, we provide evidence that a tobacco syntaxin is rapidly and transiently phosphorylated after Avr9 elicitation. The syntaxin was detected with an antibody against NtSyp121, a plasma membrane-localized syntaxin implicated in abscisic acid responses and secretion. Consistent with the gene-for-gene hypothesis, syntaxin phosphorylation required the presence of both Avr9 and Cf-9. This phosphorylation event occurred either upstream of the pathway leading to reactive oxygen species production or in a parallel pathway. Interestingly, rapid syntaxin phosphorylation was triggered by the race-specific elicitor Avr9 but not by flg22P.aer, a general elicitor capable of inducing other defense-related signaling events in Cf9 tobacco such as reactive oxygen species production, mitogen-activated protein kinase activation, and PR5 transcript up-regulation. Furthermore, NtSyp121 transcript levels were increased at 24 h after elicitation with Avr9 but not with flg22P.aer. Because most other previously described Avr9- and flg22P.aer-elicited responses are similar, syntaxin phosphorylation and NtSyp121 transcript up-regulation may serve as novel early biochemical and late molecular markers, respectively, to elucidate further differences in the signaling responses between these two elicitors.
1 This work was supported by the Gatsby Charitable Foundation (to A.H., A.A.L., and J.D.G.J.), a European Molecular Biology Organization long-term fellowship (to A.H.), and a Marie-Curie fellowship (to A.A.L.). 2 Present address: Centre for Molecular Plant Biology, Eberhard-Karls-University of Tübingen, Auf der Morgenstelle 5, 72076 Tübingen, Germany. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.063032. * Corresponding author; e-mail jonathan.jones{at}sainsbury-laboratory.ac.uk; fax 441603450011. Received March 21, 2005; returned for revision May 12, 2005; accepted May 13, 2005. This article has been cited by other articles:
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