Biosynthesis of Abscisic Acid in the Fungus Cercospora cruenta: Stimulation of Biosynthesis by Water Stress and Isolation of a Transgenic Mutant with Reduced Biosynthetic Capacity

The rate of synthesis of abscisic acid (ABA) by the phytopathogenicfungus Cercospora cruenta was found to be increased 2.6-foldby water stress (0.5 M mannitol, 48 h). To characterize theoxidative steps in the synthesis of ABA by C. cruenta, a mutantstrain deficient in the synthesis of ABA was isolated aftertransformation with a foreign gene. This strain was furthercharacterized by an immunoassay using a monoclonal antibodyspecific for 1',4'-dihydroxy--ionylidene-acetate. One transformantthat seemed likly to be deficient in the synthesis of ABA wasisolated. Integration of the foreign gene into the chromosomalDNA of the transformant was confirmed by Southern hybridization. ³Present address: Nitto Chemical Industries Co. Ltd.Chiyodaku,Tokyo, 100 Japan