The potential role of PR-8 gene of apple fruit in the mode of action of the yeast antagonist, Candida oleophila, in postharvest biocontrol of Botrytis cinerea

• Apple PR-8 gene was induced in response to Botrytis cinerea and Candida oleophila.
• The PR-8 gene was synthesized and cloned into a Pichia pastoris expression system.
• The PR-8 protein had a direct inhibitory effect on B. cinerea.

Several pathogenesis-related (PR) genes of apple have been cloned and their response to different pathogens has been studied. Different PR genes, however, may have a variable response depending on the specific organ or tissue as well as microbe. The objective of the current study was to characterize the expression of specific apple PR genes in fruit tissues in response to the antagonistic yeast, Candida oleophila (a common postharvest biocontrol agent), and the fungal pathogen, Botrytis cinerea (a major postharvest pathogen). Apple PR-5 and PR-8 gene expression was characterized in fruit in response to C. oleophila and B. cinerea. Results indicated that PR-8 expression was significantly elevated in response to both fungi. In contrast, neither C. oleophila nor B. cinerea treatment markedly affected PR-5 expression. The PR-8 gene was then synthesized and cloned into a Pichia pastoris expression system to study the antifungal activity of the PR-8 protein against B. cinerea both in vitro and in vivo. Collectively, the PR-8 gene of apple is associated with the response to B. cinerea infection, and may play a role in the mechanism by which C. oleophila effectively inhibits B. cinerea disease in apple fruit, namely by the induction of this specific host PR gene.