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Title: Phytophthora infestans effectors IPI-O1 and IPI-O4 each contribute to pathogen virulence

Author
item CHEN, YU - University Of Wisconsin
item Halterman, Dennis

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2016
Publication Date: 5/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5669936
Citation: Chen, Y., Halterman, D.A. 2017. Phytophthora infestans effectors IPI-O1 and IPI-O4 each contribute to pathogen virulence. Phytopathology. 107(5):600-606. doi: 10.1094/PHYTO-06-16-0240-R.

Interpretive Summary: The potato late blight resistance (R) gene RB is distinct from most plant R genes in that it confers resistance to a broad spectrum of pathogen isolates. RB recognizes the presence of members of the Phytophthora infestans effector family IPI-O to elicit resistance. In this manuscript, we investigate the contribution that IPI-O effectors make to pathogen growth in infected tissue. We found that both IPI-O1 and IPI-O4 effectors contribute to increased disease symptoms in the absence of the RB gene. Also, increased expression of IPI-O correlates with an increase in pathogen disease symptoms.

Technical Abstract: 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.