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Characterization of the Exoglucanase-Encoding Gene PaEXG2 and Study of Its Role in the Biocontrol Activity of Pichia anomala Strain K

September 2003 , Volume 93 , Number  9
Pages  1,145 - 1,152

Cathy Grevesse , Philippe Lepoivre , and Mohamed Haïssam Jijakli

Unité de Phytopathologie, Faculté Universitaire des Sciences Agronomiques, 2, Passage des Déportés, B-5030 Gembloux, Belgium

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Accepted for publication 8 April 2003.

The PaEXG2 gene, encoding an exo-β-1,3-glucanase, was isolated from the biocontrol agent Pichia anomala strain K. PaEXG2 has the capacity for coding an acidic protein of 427 amino acids with a predicted molecular weight of 45.7 kDa, a calculated pI of 4.7, and one potential N-glycosylation site. PaEXG2 was disrupted by the insertion of the URA3 marker gene, encoding orotidine monophosphate decarboxylase in strain KU1, a uracil auxotroph derived from strain K. Strain KU1 showed inferior biocontrol activity and colonization of wounds on apples, compared to the prototrophic strain. Antagonism and colonization were recovered after the restoration of prototrophy by transformation with the URA3 gene. Integrative transformation was shown to be mostly ectopic in strain K descendants (only 4% of integration by homologous recombination). PaEXG2 disruption abolished all detectable extracellular exo-β-1,3-glucanase activity in vitro and in situ but did not affect biocontrol of Botrytis cinerea on wounded apples.

Additional keywords: biocontrol mechanisms, biological control, gray mold, hydrolytic enzyme, mycoparasitism, postharvest apples.

© 2003 The American Phytopathological Society