Plant TRAF Proteins Regulate NLR Immune Receptor Turnover

• Genes encoding TRAF domain-containing proteins are highly expanded in higher plants
• Loss of MUSE13 and MUSE14 leads to higher NLR levels and pathogen resistance
• MUSE13 homo-oligomerizes and associates with NLRs and SCFCPR1 in planta
• A likely plant TRAFasome with MUSE13/14, SCFCPR1 and NLRs modulates NLR homeostasis

SummaryIn animals, Tumor necrosis factor receptor-associated factor (TRAF) proteins are molecular adaptors that regulate innate and adaptive immunity, development, and abiotic stress responses. Although gene families encoding TRAF domain-containing proteins exhibit enriched diversity in higher plants, their biological roles are poorly defined. Here, we report the identification of two redundant TRAF proteins, Mutant, snc1-enhancing 13 (MUSE13) and MUSE14, that contribute to the turnover of nucleotide-binding domain and leucine-rich repeat-containing (NLR) immune receptors SNC1 and RPS2. Loss of both MUSE13 and MUSE14 leads to enhanced pathogen resistance, NLR accumulation, and autoimmunity, while MUSE13 overexpression results in reduced NLR levels and activity. In planta, MUSE13 associates with SNC1, RPS2, and the E3 ubiquitin ligase SCFCPR1. Taken together, we speculate that MUSE13 and MUSE14 associate with the SCF E3 ligase complex to form a plant-type TRAFasome, which modulates ubiquitination and subsequent degradation of NLR immune sensors to maintain their homeostasis.

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