|Artlip, Timothy - Tim|
|Norelli, John (jay) - Jay|
Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2013
Publication Date: 6/7/2013
Publication URL: http://handle.nal.usda.gov/10113/57022
Citation: Liu, J., Wisniewski, M.E., Artlip, T.S., Sui, Y., Jiang, A., Droby, S., Norelli, J.L., Hu, W. 2013. The potential role of PR-8 gene of apple fruit in the mode of action of yeast antagonist, Candida oleophila, in postharvest biocontrol of Botrytis cinerea. Postharvest Biology and Technology. 85:203-209. Interpretive Summary: Developing alternative approaches to disease control is a critical objective of NP-303, Plant Diseases, due to consumer demands to lower exposure to chemicals, and reducing the impact of agriculture on the environment. In the past decade, USDA-ARS has identified several species of yeasts that can be used as biocontrol agents against postharvest diseases of fruit. At least one of these yeast species was previously commercialized, and other international research programs and commercial companies have also developed postharvest biocontrol products. Despite these options, use of these products remains limited partly due to variable performance. Therefore, there is a need to better understand the biology of biocontrol systems (host-pathogen-biocontrol agent) in order to develop strategies to increase the efficacy of biocontrol agents under a wide array of environmental conditions. In the present study, we examined the expression of an apple disease resistance gene (PR-8) in response to the grey mold pathogen (Botrytis cinerea) and whether the expression of this gene and secretion of the coded protein could enhance the biocontrol activity of yeast. PR-8 codes for a chitinase, an enzyme that degrades the cell wall of fungi. We isolated the PR-8 gene from apple and put it in a yeast expression system that would allow the yeast to secrete the protein outside the cell. Results indicated that PR-8 is upregulated in response to the grey mold pathogen and is also stimulated to a high level by the yeast biocontrol agent, Candida oleophila. Futhermore, when this gene was used in a yeast-expression system, the resulting yeast also inhibited the grey mold pathogen both in a test tube system (in vitro) and in apple fruit itself (in planta). This information will be used to develop strategies to increase natural resistance in harvested apple fruit and increase the efficacy of yeasts used as biocontrol agents.
Technical Abstract: Several pathogenesis-related (PR) genes of apple have been cloned and identified in response to specific pathogens. However, different PR genes in certain organs of specific host may be involved in specific interaction with different microbes. Current research is aimed at characterizing specific PR gene(s) of apple fruit in response to the antagonistic yeast, Candida oleophila (a common postharvest biocontrol agent), and the fungal pathogen, Botrytis cinerea (a devastating pathogen of apple fruit). We examined the gene expression of PR-5 and PR-8 of apple fruit in response to C. oleophila and B. cinerea. Results showed that PR-8 expression was stimulated significantly by both microbes, on contrary, neither C. oleophila nor B. cinerea treatment markedly changed PR-5 expression. Thus, PR-8 gene was furthermore synthesized and transformed into Pichia pastoris expression system to characterize its antifungal activity against B. cinerea both in vitro and in vivo. Collectively, the results indicated that PR-8 gene of apple fruit was associated with the response to B. cinerea infection, and the possible mode of action by which C. oleophila effectively controlled B. cinerea disease in apple fruit is the induction of this specific host PR gene, PR-8.