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JXB Advance Access published online on April 4, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern044
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© The Author [2008]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Silencing of acidic pathogenesis-related PR-1 genes increases extracellular β-(1->3)-glucanase activity at the onset of tobacco defence reactions

Marie-Pierre Rivière1 *, Antoine Marais1, Michel Ponchet1, William Willats2 and Eric Galiana1,{dagger}

1UMR 1301 Interactions Biotiques et Santé Végétale, INRA-Université Nice-SophiaAntipolis-CNRS, F-06903 Sophia Antipolis Cedex, France
2Department of Plant Physiology, Institute of Molecular Biology and Physiology, The University of Copenhagen, DK-1353 Copenhagen, Denmark

{dagger} To whom correspondence should be addressed. E-mail: galiana{at}sophia.inra.fr

The class 1 pathogenesis-related (PR) proteins are thought to be involved in plant defence responses, but their molecular functions are unknown. The function of PR-1 was investigated in tobacco by generating stable PR-1a-silenced lines in which other acidic PR-1 genes (PR-1b and PR-1c) were silenced. Plants lacking extracellular PR-1s were more susceptible than wild-type plants to the oomycete Phytophthora parasitica but displayed unaffected systemic acquired resistance and developmental resistance to this pathogen. Treatment with salicylic acid up-regulates the PR-1g gene, encoding a basic protein of the PR-1 family, in PR-1-deficient tobacco, indicating that PR-1 expression may repress that of PR-1g. This shows that acidic PR-1s are dispensable for expression of salicylic acid-dependent acquired resistances against P. parasitica and may reveal a functional overlap in tobacco defence or a functional redundancy in the PR-1 gene family. The data also show that there is a specific increase in apoplastic β-(1->3)-glucanase activity and a decrease in β-(1->3)-glucan deposition in PR-1-silenced lines following activation of defence reactions. Complementation of the silencing by apoplastic treatment with a recombinant PR-1a protein largely restores the wild-type β-(1->3)-glucanase activity and callose phenotype. Taken together with the immunolocalization of PR-1a to sites of β-(1->3)-glucan deposition in wild-type plants, these results are indicative of a function for PR-1a in regulation of enzymatic activity of extracellular β-(1->3)-glucanases.

Key words: ARR, callose, β-(1->3)-glucanase, PR-1a, RNAi, SAR

* Present address: Departamento de Biotecnología-UPM, E.T.S. Ingenieros Agrónomos, Avda. Complutense, E-28040 Madrid, Spain.

Received 12 November 2007; Revised 8 January 2008 Accepted 21 January 2008


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