He published 12 separate documents based on his thesis work, which merited him a job teaching at University of California, Riverside (UCR) despite not having any postdoctoral experience.

[11] Keen studied the biochemical interactions responsible for resistance to Phytophthora sojae in one cultivar of soybean but not another, publishing the first findings on the subject in 1975.

[15][16] The two had worked together in 1980 at the International Plant Research Institute in San Carlos, California in order to use recombinant DNA techniques to clone bacterial avirulence genes.

[17] In 2000, an image of Keen standing next to the parallel β-helix structure of pectate lyase C was added as part of the Gluck Gateway Mural positioned under the California State Route 60 overpass between the University campus and the city of Riverside.

[18] Keen had discovered the parallel helix to be pectate lyase C's third folding form during a collaboration with X-ray crystallographers studying Erwinia chrysanthemi.

[5] The American Phytopathological Society awards an annual cash prize in Keen's name for "research excellence in molecular plant pathology.