An activated form of NB-ARC protein RLS1 functions with cysteine-rich receptor-like protein RMC to trigger cell death in rice

A key event that follows pathogen recognition by a resistance (R) protein containing an NB-ARC (nucleo-tide-binding adaptor shared by Apaf-1, R proteins, and Ced-4) domain is hypersensitive response (HR) -type cell death accompanied by accumulation of reactive oxygen species and nitric oxide. However, the integral mechanisms that underlie this process remain relatively opaque. Here, we show that a gain-of -function mutation in the NB-ARC protein RLS1 (Rapid Leaf Senescence 1) triggers high-light-dependent HR-like cell death in rice. The RLS1-mediated defense response is largely independent of salicylic acid accumulation, NPR1 (Nonexpressor of Pathogenesis-Related Gene 1) activity, and RAR1 (Required for Mla12 Resistance 1) function. A screen for suppressors of RLS1 activation identified RMC (Root Meander Curling) as essential for the RLS1-activated defense response. RMC encodes a cysteine-rich receptor-like secreted protein (CRRSP) and functions as an RLS1-binding partner. Intriguingly, their co-expression resulted in a change in the pattern of subcellular localization and was sufficient to trigger cell death accom-panied by a decrease in the activity of the antioxidant enzyme APX1. Collectively, our findings reveal an NB-ARC-CRRSP signaling module that modulates oxidative state, the cell death process, and associated im-munity responses in rice.

Automated summary

A mutation in the NB-ARC protein RLS1 triggers HR-like cell death in rice, which is independent of salicylic acid accumulation, NPR1 activity, and RAR1 function. RMC, encoding a CRRSP protein and functioning as an RLS1-binding partner, is essential for the RLS1-activated defense response. Co-expression of RMC and RLS1 leads to changes in subcellular localization and cell death accompanied by a decrease in APX1 activity.