Processing, targeting, and antifungal activity of stinging nettle agglutinin in transgenic tobacco

The gene encoding the precursor to stinging nettle (Urtica dioica L.) isole ctin I was introduced into tobacco (Nicotiana tabacum). In transgenic plant s this precursor was processed to mature-sized lectin. The mature isolectin is deposited intracellularly, most likely in the vacuoles. A gene construc t lacking the C-terminal 25 amino acids was also introduced in tobacco to s tudy the role of the C terminus in subcellular trafficking. In tobacco plan ts that expressed this construct the mutant precursor was correctly process ed and the mature isolectin was targeted to the intercellular space. These results indicate the presence of a C-terminal signal for intracellular rete ntion of stinging nettle lectin and most likely for sorting of the lectin t o the vacuoles. In addition, correct processing of this lectin did not depe nd on vacuolar deposition. Isolectin I purified from tobacco displayed iden tical biological activities as isolectin I isolated from stinging nettle. I n vitro antifungal assays on germinated spores of the fungi Botrytis cinere a, Trichoderma viride, and Colletotrichum lindemuthianum revealed that grow th inhibition by stinging nettle isolectin I occurs at a specific phase of fungal growth and is temporal, suggesting that the fungi had an adaptation mechanism.