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PLANTS INTERACTING WITH OTHER ORGANISMS

Role of Swollenin, an Expansin-Like Protein from Trichoderma, in Plant Root Colonization^1,[W]

Department of Plant Pathology and Microbiology, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel (Y.B., E.B., A.V., I.C.); and Department of Plant Science, The Weizmann Institute of Science, 76100 Rehovot, Israel (Y.B.)

Swollenin, a protein first characterized in the saprophytic fungus Trichoderma reesei, contains an N-terminal carbohydrate-binding module family 1 domain (CBD) with cellulose-binding function and a C-terminal expansin-like domain. This protein was identified by liquid chromatography-mass spectrometry among many other cellulolytic proteins secreted in the coculture hydroponics medium of cucumber (Cucumis sativus) seedlings and Trichoderma asperellum, a well-known biocontrol agent and inducer of plant defense responses. The swollenin gene was isolated and its coding region was overexpressed in the same strain under the control of the constitutive pki1 promoter. Trichoderma transformants showed a remarkably increased ability to colonize cucumber roots within 6 h after inoculation. On the other hand, overexpressors of a truncated swollenin sequence bearing a 36-amino acid deletion of the CBD did not differ from the wild type, showing in vivo that this domain is necessary for full protein activity. Root colonization rates were reduced in transformants silenced in swollenin gene expression. A synthetic 36-mer swollenin CBD peptide was shown to be capable of stimulating local defense responses in cucumber roots and leaves and to afford local protection toward Botrytis cinerea and Pseudomonas syringae pv lachrymans infection. This indicates that the CBD domain might be recognized by the plant as a microbe-associated molecular pattern in the Trichoderma-plant interaction.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Ada Viterbo (viterbo{at}agri.huji.ac.il).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.116293

^* Corresponding author; e-mail viterbo{at}agri.huji.ac.il.

Received January 13, 2008; accepted April 2, 2008; published April 9, 2008.

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