POTATO ASPARTIC PROTEASES: INDUCTION, ANTIMICROBIAL ACTIVITY AND SUBSTRATE SPECIFICITY

Abstract

SUMMARY Plant aspartic proteinases (EC 3. 4. 23) have been associated with abiotic stress responses, but little is known about their possible involvement in biotic stress responses. Here we report the induction of an aspartic proteinase, StAP3 (Solanum tuberosum aspartic protease), in potato leaves upon infection with Phytophthora infestans and we compare its antimicrobial activity and substrate specificity whith StAP1, an aspartic protease from potato tubers previously characterized. Both the aspartic proteinase content and activity were significantly increased in leaves from a resistant cultivar (cv Pampeana) as compared to a susceptible one (cv Bintje). In vitro analysis shows that StAP3 has antimicrobial activity towards P. infestans and Fusarium solani, like StAP1 from tubers. Substrate specificity of StAP1 and StAP3 was studied, using oxidized insuline b-chain as substrate. Both enzymes have a common cleavage position, like other plant aspartic proteases. Additionally, StAP1 has other two cleavage positions and StAP3 was able to cleave the peptide bond Phe 24 -Phe 25 , a cleavage position found in other plant APs. The induction of both StAPs (StAP1 and StAP3) in potato tubers and leaves after wounding and infection in potato resistant cultivars and their antimicrobial activity would suggest that these StAPs are involved in plant defense response. In a previous paper, StAPs antimicrobial activity was ascribed to StAPs proteolytic activity. Differences in the antimicrobial activity of StAP1 and StAP3 may be associated with the differences found in the substrate specificity between these enzymes.