James Tokuhisa

Major Field of Interest

Biochemical and molecular mechanisms of chemical defense fitness in higher plants

Current Research

My lab focuses on two chemical defense systems that protect plants from attack by generalist herbivores.  Crucifer plants produce glucosinolates, nontoxic glycosides, that are bioactivated when herbivores attack the plant.  We humans recognize these bioactivated compounds as the sharp flavor components of arugula, horseradish , mustard, and wasabi.  The bioactivating agent is an enzyme that is heavily modified after it has been synthesized in the plant.  We are investigating how these unusual post-translational modifications contribute to plant fitness in plant-herbivore interactions. 

Plants of the Solanum genus produce steroidal glycoalkaloids as defense compounds against generalist herbivores.  These compounds are the bitter flavors we associate with unripe tomatoes and the jackets of red potato tubers.  The production of these compounds requires increased metabolic flux through the terpenoid biosynthetic pathway.  The enzyme squalene synthase is a critical enzyme of this pathway and in potato is encoded by an unusually large gene family.  We are looking at the individual members of the gene family to identify biochemical and molecular features that contribute to the biosynthesis of the steroidal defense compounds.