A key role for <i>S-</i> nitrosylation in immune regulation and development in the liverwort <i>Marchantia polymorpha</i>

Nitric oxide (NO) is an important signaling molecule in flowering plant immunity. It rapidly accumulates in response to pathogen perception. In addition to it's direct response to microbes, NO controls a range of defence responses primarily through S-nitrosylation. This process is a redox-dependent modification where a NO group attaches to the thiol of a cysteine residue, creating an S-nitrosothiol (SNO). To explore the role of S-nitrosylation more broadly, we characterised the single-copy S-nitrosoglutathione reductase 1 (MpGSNOR1) gene in the liverwort Marchantia polymorpha (Marchantia), a representative of a lineage widely diverged from flowering plants. We generated loss-of-function alleles using CRISPR/Cas9 genome editing. Disrupting MpGSNOR1 resulted in pronounced morphological alterations, highlighting the role of GSNOR1 in the structural development of Marchantia. Additionally, we show that MpGSNOR1 is essential for SNO homeostasis and immune function. Our results suggest that GSNOR was part of the tool kit of the ancestral land plant and functioned in immunity and development.