S-Nitrosoproteome Analysis of Rice Leaves Highlights the Possible Roles of Superoxide Dismutase in Resistance Against...

Nitric oxide (NO) is a key signaling molecule and is known to modulate diverse physiological processes, including defense responses against pathogens. However, the molecular mechanism underlying NO-induced plant immunity remains largely elusive. Here, we investigated the dynamics of NO biosynthesis and its downstream signaling through S-nitrosoproteome analysis of two rice cultivars, Dongjin (DJ, resistant) and Nipponbare (NIP, susceptible), in response to Magnaporthe oryzae, the causative agent of the rice blast disease. M. oryzae inoculation triggered relatively higher nitric oxide synthase (NOS/NOA1)-mediated NO biosynthesis in DJ than that of NIP. High-throughput, site-specific S-nitrosoproteome analysis using the iodoTMT-based mass spectrometry approach led to the identification of 511 S-nitrosated peptides corresponding to 335 proteins, representing the most comprehensive set of S-nitrosated peptides identified in rice so far. In particular, the S-nitrosated site intensity of superoxide dismutase (SOD) at Cysteine²⁶³ was significantly reduced specifically in DJ in response to pathogen inoculation. We observed that in vitro S-nitrosation of SOD enhances its activity, and its M. oryzae infection-triggered denitrosation was correlated with the S-nitrosoglutathione reductase (GSNOR) activation. This denitrosation-mediated suppression of SOD activity likely leads to the accumulation of superoxide ions during infection, which triggers immune responses. Altogether, our results suggest that NO-mediated S-nitrosation of SOD plays a crucial role in orchestrating redox-dependent defense signaling, which likely contributes to the contrasting resistance responses observed in the two cultivars. These findings provide novel insights into the functional implications of S-nitrosation in plant immunity and highlight redox-regulatory proteins as key targets of NO signaling during pathogen challenge.