COLONIZATION OF TRANSGENIC NICOTIANA-SYLVESTRIS PLANTS, EXPRESSING DIFFERENT FORMS OF NICOTIANA-TABACUM CHITINASE, BY THE ROOT PATHOGEN RHIZOCTONIA-SOLANI AND BY THE MYCORRHIZAL SYMBIONT GLOMUS-MOSSEAE

Transgenic plants constitutively expressing bean chitinase have been shown to display enhanced resistance to the root pathogen Rhizoctonia solani (K. Broglie, I. Chet, M. Holliday, R. Cressman, P. Biddle, S. Knowlton, C. J. Mauvis, and R. Broglie, Science 254:1194-1197, 1991). We used transgenic Nicotiana sylvestris plants, expressing different forms of tobacco chitinase under the control of the expression signals of the 35S transcript of cauliflower mosaic virus, to compare the colonization of the root system by R. solani and by the mycorrhizal symbiont Glomus mosseae. Plants of N. sylvestris expressing the vacuolar tobacco chitinase A or the same chitinase without the N-terminal chitin binding domain were less colonized by R. solani than control plants and showed less reduction of the root fresh weight when exposed to an attack of this fungus. Plants of N. sylvestris expressing chitinase A without the C-terminal signal for vacuolar targeting showed no enhanced resistance since they were colonized by R. solani like control plants. All transgenic N. sylvestris investigated were equally well colonized by G. mosseae, indicating that the enhanced resistance conferred by constitutive expression of chitinase in transgenic plants does not interfere with the vesicular-arbuscular mycorrhizal symbiosis.