The Deubiquitinating Enzyme AMSH1 Contributes to Plant Immunity Through Regulating the Stability of BDA1

Plants utilize plasma membrane localized receptors like kinases (RLKs) or receptor-like proteins (RLPs) to recognize pathogens and activate pattern-triggered immunity (PTI) responses. A gain-of-function mutation in the <i>Arabidopsis</i> RLP <i>SNC2 (SUPPRESSOR OF NPR1-1, CONSTITUTIVE 2)</i> leads to constitutive activation of defense responses in <i>snc2-1D</i> mutant plants. Transcription factors, SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) and CALMODULIN-BINDING PROTEIN 60g (CBP60g), define two parallel pathways downstream of SNC2. The autoimmunity of <i>snc2-1D</i> was partially affected by single mutations in <i>SARD1</i> or <i>CBP60g</i> but completely suppressed by the <i>sard1 cbp60g</i> double mutant. From a suppressor screen using <i>sard1-1 snc2-1D</i>, we identified a deubiquitinating enzyme ASSOCIATED MOLECULE WITH THE SH3 DOMAIN OF STAM 1 (AMSH1) as a key component in SNC2-mediated plant immunity. A loss-of-function mutation in <i>AMSH1</i> can suppress the autoimmune responses of <i>sard1-1 snc2-1D</i>. In eukaryotes, selective protein degradation often occurs through the ubiquitination/deubiquitination system. The deubiquitinating enzymes that remove ubiquitin from target proteins play essential roles in controlling the level of target protein ubiquitination and degradation. As loss of <i>AMSH1</i> results in decreased BDA1 abundance and BDA1 is a transmembrane protein required for SNC2-mediated immunity, AMSH1 likely contributes to immunity regulation through controlling BDA1 stability.