Cysteine thiol sulfinic acid in plant stress signaling.

Cysteine thiols are susceptible to various oxidative posttranslational modifications (PTMs) due to their high chemical reactivity. Thiol-based PTMs play a crucial role in regulating protein functions and are key contributors to cellular redox signaling. Although reversible thiol-based PTMs, such as disulfide bond formation, S-nitrosylation, and S-glutathionylation, have been extensively studied for their roles in redox regulation, thiol sulfinic acid (-SO 2 H) modification is often perceived as irreversible and of marginal significance in redox signaling. Here, we revisit this narrow perspective and shed light on the redox regulatory roles of -SO 2 H in plant stress signaling. We provide an overview of protein sulfinylation in plants, delving into the roles of hydrogen peroxide-mediated and plant cysteine oxidase-catalyzed formation of -SO 2 H, highlighting the involvement of -SO 2 H in specific regulatory signaling pathways. Additionally, we compile the existing knowledge of the -SO 2 H reducing enzyme, sulfiredoxin, offering insights into its molecular mechanisms and biological relevance. We further summarize current proteomic techniques for detecting -SO 2 H and furnish a list of experimentally validated cysteine -SO 2 H sites across various species, discussing their functional consequences. This review aims to spark new insights and discussions that lead to further investigations into the functional significance of protein -SO 2 H-based redox signaling in plants.