PROTEOLYTIC PROCESSING OF CLASS-IV CHITINASE IN THE COMPATIBLE INTERACTION OF BEAN ROOTS WITH FUSARIUM-SOLANI

Three chitinase isoenzymes, PvChiE, PvChiF, and PvChiG (molecular mass es 29, 28, and 27 kD, respectively), were purified from bean (Phaseolu s vulgaris L. cv Saxa) roots infected with the fungal pathogen Fusariu m solani f. sp. phaseoli, and their amino acid sequence was partially determined. All sequences from all three isoenzymes exactly matched de duced amino acid sequences of the bean class IV chitinase PvChi4, form erly called PR4. The N terminus of PvChiF mapped to the hinge region, and the N terminus of PvChiG mapped to the catalytic domain of PvChi4. The N terminus of PvChiE was blocked. The appearance of PvChiE, PvChi F, and PvChiG correlated with an increase in protease activity in infe cted roots, and they could be generated in vitro by mixing extracts wi th high protease activity with extracts containing high amounts of PvC hi4. Extracts from infected roots prepared in the presence of protease inhibitors also contained the processed forms of PvChi4, indicating t hat processing occurred in planta and not as an artifact of extraction . Processing of PvChi4 was not detected in incompatible interactions w ith a nonhost strain of F. solani and in symbiotic interactions with G lomus mosseae, and thus may be important only in compatible interactio ns with F. solani.