The AvrSen1 Triggers a Hypersensitive Response in Potatoes While Natural Variants Evade Detection.

is an obligate biotrophic fungus of division Chytridiomycota. It causes potato wart disease, has a worldwide quarantine status and is included on the Health and Human Services and United States Department of Agriculture Select Agent list. isolates are grouped in pathotypes based on their ability to evade host resistance in a set of differential potato varieties. Thus far, 39 pathotypes are reported. A single dominant gene () governs pathotype 1 (D1) resistance and we anticipated that the underlying molecular model would involve a pathogen effector (AvrSen1) that is recognized by the host. The -specific secretome of 14 isolates representing six different pathotypes was screened for effectors specifically present in pathotype 1 (D1) isolates but absent in others. We identified a single candidate. Expression of this candidate in potato plants showed a specific hypersensitive response (HR), which cosegregated with the resistance in potato populations. No HR was obtained with truncated genes found in pathotypes that evaded recognition by . These findings established that our candidate gene was indeed The is a single-copy gene and encodes a 376-amino-acid protein without predicted function or functional domains, and is the first effector gene identified in Chytridiomycota, an extremely diverse yet underrepresented basal lineage of fungi.