Functional Characterization of Protease Inhibitor SlPinII5 in Tomato Resistance to Late Blight

Tomato yield and quality are severely threatened by late blight caused by Phytophthora infestans. Enhancing natural disease resistance offers a sustainable alternative to chemical control. Proteinase inhibitor II (PinII) has emerged as a promising candidate for improving plant resistance. However, the functional basis of their role in tomato defense remains largely unclear. In this study, 12 SlPinII genes were identified, and SlPinII5 was selected for its strong response to P. infestans. Functional analyses showed that SlPinII5 enhances tomato resistance by activating defense-related genes, modulating enzyme activities, and regulating reactive oxygen species. Enrichment analysis of differentially expressed genes indicated that SlPinII5 is involved in regulating several disease resistance-related pathways. Moreover, purified SlPinII5 directly inhibited P. infestans growth and reduced infection in tomato leaves and fruits. These findings indicate that SlPinII5 positively regulates tomato defense, providing insights for resistance breeding and sustainable disease management.