Role of SNC1 and Nitrate reductase activity on autoimmunity in the SUMO E3 ligase mutant siz1
H. VAN DEN BURG (1), V. Hammoudi (1), G. Vlachakis (1), S. Chatterjee (1), B. Beerens (1) (1) University of Amsterdam, Netherlands

Attachment of Small Ubiquitin-like modifier (SUMO) to substrates is an essential protein modification in Arabidopsis affecting +400 proteins. Especially, the E3 ligase SIZ1 controls SUMO conjugation to many of these substrates in response to e.g. heat stress. Loss of SIZ1 (siz1-2) triggers activation of Salicylic-acid (SA) dependent autoimmunity via PAD4/EDS1 (Lee et al., 2007). SIZ1 stimulates NIA1/NIA2 nitrate reductase activity (Park et al., 2011), but the question remains if sumoylation of NIA1/NIA2 is causal to siz1 phenotype. Feeding with ammonia but not nitrate suppressed PR1/2 gene expression in siz1. The ammonium/nitrate ratio also acts an input signal for autoimmunity triggered by SNC1 (a TIR-NB-LRR type protein) up-regulation (Wang et al., 2013). We used genetics to examine whether SNC1 and/or NIA1/NIA2 are also required for siz1 autoimmunity. We find that primarily the SNC1 autoimmune phenotype depends on ammonia availability, while the siz1-phenotype does not. Moreover, SNC1 is essential for microlession formation but not for PR1/2 accumulation in siz1. We conclude that SNC1 and NO signaling act downstream of PAD4/EDS1 in siz1, affecting a subset of its defense phenotype.

Abstract Number: P16-476
Session Type: Poster