System for Simultaneous Study of Bacterial and Plant Gene Expression in Soft Rot of Potato. Z. Yang. Laboratory for Molecular Biology of Plant Stress, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0330 U.S.A. C. L. Cramer, and G. H. Lacy. Laboratory for Molecular Biology of Plant Stress, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0330 U.S.A. MPMI 2:195-201. Accepted 16 March 1989. Copyright 1989 The American Phytopathological Society.

An experimental system using potato tuber slices and Erwinia carotovora subsp. carotovora was developed to study simultaneous in planta regulation of bacterial and plant genes in soft rot interactions. This system involves inoculation of tuber slices with E. c. subsp. carotovora separated from host tissue by a biologically inert polysulfone membrane. This arrangement gives reproducible development of tissue maceration and permits rapid and quantitative isolation of bacteria free of plant cells and debris and isolation of bacteria-free plant cells. Similar tissue maceration and plant and bacterial gene induction occurred in membrane-separated versus direct-contact interactions. Northern hybridization showed increases in E. c. subsp. carotovora pectate lyase (PL) mRNA levels 4 hr after inoculation with maximum levels at 9 hr. PL activity, monitored by isoelectric-focused activity overlays, was induced within 2 hr and increased through 24 hr and was consistent with mRNA transcription and maceration patterns. Host defense responses were monitored by phenylalanine ammonia-lyase (PAL) activity and mRNA levels. Tuber mRNAs (2.4 to 2.6 kb) hybridized with bean PAL cDNA sequences. Induction of PAL enzyme activity and mRNA levels was greater and more rapid in tuber slices inoculated with E. c. subsp. carotovora compared with noninoculated slices suggesting that E. c. subsp. carotovora triggers active host defense responses superimposed upon wound responses.