Peroxynitrite-mediated tyrosine nitration modulates β-1,3-glucanase activity and potato defense against Phytophthora infestans

Protein tyrosine nitration is a well-documented peroxynitrite (ONOO – )- mediated post-translational modification (PTM) in biological systems; however, its relevance in plant immune response remains poorly understood. In this study, a potato–avr/vr Phytophthora infestans system was used as a model to investigate the functional consequences of protein tyrosine nitration. This work shows that only the potato-avr P. infestans interaction is accompanied by an early and transient accumulation of nitrated proteins, observed within the first 6 hpi. In turn, the vr P. infestans pathosystem exhibited a delayed and prolonged accumulation of nitrated protein with maximum levels coinciding with tissue colonization. Two-dimensional gel electrophoresis coupled with immunodetection identified β-1,3-glucanase (PR-2), a key enzyme in plant resistance, as one of the main targets of tyrosine nitration. Functional studies using recombinant β-1,3-glucanase demonstrated that peroxynitrite-mediated nitration directly inhibits enzymatic activity. In silico structural analysis indicated that Tyr59 in the catalytic pocket emerges as a key regulatory site. Collectively, these results suggest that protein tyrosine nitration represents a dynamic and selective regulatory mechanism in potato immunity.