Journal Article

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

Marie-Pierre Rivière, Antoine Marais, Michel Ponchet, William Willats and Eric Galiana

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 6, pages 1225-1239
Published in print April 2008 | ISSN: 0022-0957
Published online April 2008 | e-ISSN: 1460-2431 | DOI:
Silencing of acidic pathogenesis-related PR-1 genes increases extracellular β-(1→3)-glucanase activity at the onset of tobacco defence reactions

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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.

Keywords: ARR; callose; β-(1→3)-glucanase; PR-1a; RNAi; SAR

Journal Article.  9657 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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