Julio C. Vega-Arreguín,1,2
Jorunn I. Bos,4,5 and
1Boyce Thompson Institute for Plant Research, Ithaca, NY, 14850, U.S.A.; 2Universidad Nacional Autónoma de México, ENES Unidad León. León, Gto. México; 3Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14850, U.S.A.; 4The James Hutton Institute, Errol Road, Invergowrie, Dundee DD2 5DA, Scotland, U.K.; 5University of Dundee, Division of Plant Sciences, University of Dundee, Dundee DD2 5DA, U.K.; 6Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
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Accepted 31 March 2014.
Nonhost resistance is a commonly occurring phenomenon wherein all accessions or cultivars of a plant species are resistant to all strains of a pathogen species and is likely the manifestation of multiple molecular mechanisms. Phytophthora capsici is a soil-borne oomycete that causes Phytophthora blight disease in many solanaceous and cucurbitaceous plants worldwide. Interest in P. capsici has increased considerably with the sequencing of its genome and its increasing occurrence in multiple crops. However, molecular interactions between P. capsici and both its hosts and its nonhosts are poorly defined. We show here that tobacco (Nicotiana tabacum) acts like a nonhost for P. capsici and responds to P. capsici infection with a hypersensitive response (HR). Furthermore, we have found that a P. capsici Avr3a-like gene (PcAvr3a1) encoding a putative RXLR effector protein produces a HR upon transient expression in tobacco and several other Nicotiana species. This HR response correlated with resistance in 19 of 23 Nicotiana species and accessions tested, and knock-down of PcAvr3a1 expression by host-induced gene silencing allowed infection of resistant tobacco. Our results suggest that many Nicotiana species have the capacity to recognize PcAvr3a1 via the products of endogenous disease resistance (R) genes and that this R gene–mediated response is a major component of nonhost resistance to P. capsici.
© 2014 The American Phytopathological Society