Determination of Virulence Contributions from Phytophthora infestans Effectors IPI-O1 and IPI-O4
Y. CHEN (1), D. Halterman (2) (1) Department of Horticulture, University of Wisconsin-Madison, U.S.A.; (2) U.S. Department of Agriculture-Agricultural Research Service, U.S.A.

Potato late blight, caused by the oomycete pathogen Phytophthora infestans, is one of the most destructive plant diseases. Despite decades of intensive breeding efforts, it remains a threat to potato production worldwide, in part because newly evolved pathogen isolates quickly overcome major resistance genes. The RB gene, cloned from the diploid wild potato species Solanum bulbocastanum, confers partial resistance to most P. infestans isolates through its recognition of the corresponding pathogen effector family IPI-O. While some family members are recognized by RB to elicit host resistance (e.g. IPI-O1, IPI-O2), some family members are able to elude detection (e.g. IPI-O4). IPI-O1 is ubiquitous in global P. infestans strains; in contrast, IPI-O4 is more rare, suggesting that IPI-O4 may have evolved later than IPI-O1. So far, no direct experimental evidence has been shown to demonstrate the virulence effect of IPI-O in the P. infestans-potato pathosystem. Here, our work has demonstrated that in planta expression of both IPI-O1 and IPI-O4 assist P. infestans to make enlarged lesions in potato leaves. We have previously found that IPI-O4 has gained the ability to suppress the HR induced by IPI-O1 in the presence of RB. In this study, our work has shown that this gain-of-function of IPI-O4 does not compromise its virulence effect. In addition, IPI-O4 assists some P. infestans stains to make larger lesions than IPI-O1. We have also found in this study that higher expression of IPI-O effectors correlates with enlarged lesions, indicating that IPI-O can contribute to virulence quantitatively.

Abstract Number: P9-257
Session Type: Poster