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Transgenic Expression of Pear PGIP in Tomato Limits Fungal Colonization

¹Department of Vegetable Crops University of California, Davis 95616-8631, U.S.A.; ²Laboratory of Phytopathology, Wageningen University, Wageningen, The Netherlands; ³Section Molecular Genetics of Industrial Microorganisms, Wageningen University, Wageningen, The Netherlands; ⁴Department of Pomology, University of California, Davis 95616-8631, U.S.A.

Transgenic tomato plants expressing the pear fruit polygalacturonase inhibitor protein (pPGIP) were used to demonstrate that this inhibitor of fungal pathogen endopolygalacturonases (endo-PGs) influences disease development. Transgenic expression of pPGIP resulted in abundant accumulation of the heterologous protein in all tissues and did not alter the expression of an endogenous tomato fruit PGIP (tPGIP). The pPGIP protein was detected, as expected, in the cell wall protein fraction in all transgenic tissues. Despite differential glycosylation in vegetative and fruit tissues, the expressed pPGIP was active in both tissues as an inhibitor of endo-PGs from Botrytis cinerea. The growth of B. cinerea on ripe tomato fruit expressing pPGIP was reduced, and tissue breakdown was diminished by as much as 15%, compared with nontransgenic fruit. In transgenic leaves, the expression of pPGIP reduced lesions of macerated tissue approximately 25%, a reduction of symptoms of fungal growth similar to that observed with a B. cinerea strain in which a single endo-PG gene, Bcpg1, had been deleted (A. ten Have, W. Mulder, J. Visser, and J. A. L. van Kan, Mol. Plant-Microbe Interact. 11:1009--1016, 1998). Heterologous expression of pPGIP has demonstrated that PGIP inhibition of fungal PGs slows the expansion of disease lesions and the associated tissue maceration.

Additional keywords: Lycopersicon esculentum, plant defenses, reducing sugar assay.