Suppression of Pisatin, Phenylalanine Ammonia-Lyase mRNA, and Chalcone Synthase mRNA Accumulation by a Putative Pathogenicity Factor from the Fungus Mycosphaerella pinodes. Testsuji Yamada. Laboratory of Plant Pathology, College of Agriculture, Okayama University, Tsushima, Okayama, 700, Japan.. Hisako Hashimoto, Tomonori Shiraishi, and Hachiro Oku. Laboratory of Plant Pathology, College of Agriculture, Okayama University, Tsushima, Okayama, 700, Japan. . MPMI 2:256-261. Accepted 1 May 1989. Copyright 1989 The American Phytopathological Society.

Effects of the fungal suppressor isolated from a pea pathogen, Mycosphaerella pinodes, were examined on pea defense reactions with respect to pisatin accumulation, phenylalanine ammonialyase (PAL) activity, and the corresponding PAL or chalcone synthase (CHS) mRNA level. Treatment of etiolated pea epicotyl tissues with elicitor activates the accumulation of PAL and CHS mRNAs within 1 hr, followed by an increase in PAL enzyme activity and in pisatin biosynthesis. Concomitant presence of suppressor with elicitor results in delays of these host defense reactions, and include a 3-hr delay in the accumulation of PAL and CHS mRNAs, a 6-hr delay in the increase of PAL enzyme activity, and a 6- to 9-hr suppression of pisatin accumulation. These results demonstrate that the fungal suppressor could play an important role in the host-parasite interaction by delaying the defense response of a plant.