Plant genomes encode numerous nucleotide-binding leucine-rich repeat receptors (NLRs) that recognise specific effectors secreted from pathogens and activate pathways leading to defence responses, including localized cell death. Plant NLRs consist of three key domains. The N-terminal signalling domain can be Toll/interleukin-1 receptor (TIR) domain, coiled-coil (CC) domain, or Resistance to Powdery Mildew 8 (RPW8) domain. A central nucleotide-binding (NB-ARC) domain is responsible for ADP/ATP binding and ATP-dependent oligomerisation. A C-terminal leucine-rich repeat (LRR) domain is required for effector recognition and auto-inhibition. Several TIR-NLRs form tetrameric oligomers upon effector binding, and function as nicotinamide adenine dinucleotide (NAD+)-cleaving enzymes mediated by TIR domains, which induces cell death in plants. It is unknown whether NADase activity is a common feature among diverse TIR-NLRs and how NAD+-cleavage initiates downstream signalling. We expressed and purified a flax TIR-NLR protein named M. Analysis by size exclusion chromatography and transmission electron microscopy suggested that the M protein was present as both oligomeric and monomeric forms, regardless of the presence or absence of its cognate effector. Future research will focus on determining cryo-EM structures of M with and without its effector. To test for NADase activity, the TIR domain of M was expressed and purified. Low levels of the NADase activity by MTIR was detected by a fluorescence assay using a fluorescent NAD+ analogue. In accordance, transient expression of MTIR in Nicotiana benthamiana did not trigger cell death, while its closely related L6TIR protein with relatively high NADase activity showed cell death. Further work is required to establish functional importance of NAD+-cleavage activity of M on cell death pathways/plant innate immunity.