Purification and Characterization of Beta₂-Tomatinase, an Enzyme Involved in the Degradation of alpha-Tomatine and Isolation of the Gene Encoding Beta₂-Tomatinase from Septoria lycopersici. Robert W. Sandrock . Department of Plant Pathology, University of Arizona, Tucson 85721, U.S.A. Dean DellaPenna (2), and Hans D. VanEtten (1). (1) Department of Plant Pathology and University of Arizona, Tucson 85721, U.S.A. (2) Department of Plant Sciences, University of Arizona, Tucson 85721, U.S.A. MPMI 8:960-970. Accepted 15 August 1995. Copyright 1996 The American Phytopathological Society.

Lycopersicon species often contain the toxic glycoalkaloid alpha-tomatine, which is proposed to protect these plants from general microbial infection. However, fungal pathogens of tomato often are tolerant to alpha-tomatine and detoxification of alpha-tomatine may be how these pathogens avoid this potential barrier. As an initial step to evaluate this possibility, we have purified to homogeneity a Beta-1,2-D glucosidase from the tomato pathogen Septoria lycopersici that hydro-lyzes the Beta-1,2-D glucosyl bond on the tetrasaccharide moiety of ( -tomatine to produce Beta ₂tomatine. The enzyme is a 110-kDa protein with a pI of 4.5 and a Km for alpha-tomaline of 62 (M. Little or no activity was detected on a variety of other glycosides. The gene encoding this protein was isolated and contains an open reading frame of 803 amino acids that shares sequence homology with several other Beta-D-glucosidases. When S. lycopersici was incubated with (-tomatine, Beta ₂tomatinase mRNA accumulated, suggesting that the enzyme is substrate inducible. Aspergillus nidulans expressed "Beta ₂tomtinase" activity when transformed with this gene but transformants were still sensitive to (-tomatine.