Submitted to: Yeast
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2003
Publication Date: 9/1/2003
Citation: YEHUDA, H., DROBY, S., BAR-SIMON, M., WISNIEWSKI, M.E., GOLDWAY, M. THE EFFECT OF UNDER- AND OVER-EXPRESSED COEXG1-ENCODED EXOGLUCANASE SECRETED BY CANDIDA OLEOPHILA ON THE BICONTROL OF PENICILLIUM DIGITATUM. YEAST. SEPTEMBER 2003, Vol. 20, pgs. 771-780. Interpretive Summary: Developing biological methods of controlling postharvest diseases of fruits and vegetables is a critical area of research that addresses the public demand for decreased use of synthetic chemicals in agriculture. Previous research has identified several yeast that displace pathogens from wounds and can be used to control postharvest rots. Some of these yeasts have been developed into commercial products by industry. Developing a better understanding of which genes in yeast play a role in biocontrol activity can lead to the selection of superior biocontrol agents. In the current study, we investigated the role of a cell-wall-degrading enzyme, exoglucanase on biocontrol activity of the yeast, Candida oleophila. The yeast was genetically engineered to overexpress or underexpress a native gene coding for an exoglucanase. This enzyme can digest cell walls of other fungi thus incapacitating them. The resulting transgenic yeast either produced higher or lower levels of the exoglucanase enzyme. The over or under expression of this enzyme had not effect on the ability of this yeast to control the postharvest pathogen Penicillium digitatum. However, these findings do not rule out the possibility that the participation of exoglucanase in biocontrol is dependent on the activity of other gene products or that the effect of this enzyme on biocontrol activity could be observed under different environmental conditions. Further research will examine the role of other genes on biocontrol activity.
Technical Abstract: The yeast, Candida oleophila, is acknowledged for its biocontrol activity against postharvest moulds. However, the mechanism of this activity is not fully understood. One of the conjectured modes of action is associated with extracellular lytic enzymes, such as b-exoglucanase. The relationship of b-exoglucanase in the biocontrol activity of C. oleophila was investigated by generating C. oleophila CoEXG1-knockouts and double-CoEXG1 transformants. The knockout transformants secreted 0-13% of the exoglucanase activity detected in the medium of the untransformed yeast (depending on the medium), indicating that CoEXG1 is the main gene responsible for the production of the secreted exoglucanase. Correspondingly, the double-CoEXG1 transformants secreted approximately twice as much 1,3-b-exoglucanase as the untransformed C. oleophila. The biocontrol activity of the CoEXG1-knockout and the double-CoEXG1 transformants against Penicillium digitatum did not differ from that of the untransformed C. oleophila on kumquats. These results imply that the 1,3-b -exoglucanase encoded by the gene CoEXG1 is not involved in the biocontrol activity of C. oleophila against P. digitatum under these experimental terms. However, these findings do not rule out the possibilities, that the participation of CoEXG1 in biocontrol is dependent on the activity of other gene products, or that its effect may be manifested under altered environmental conditions.