Abstract:
Plants possess an arsenal of immune receptors to allow for numerous tiers of
defense against pathogen attack. These immune receptors can be located either
in the nucleocytoplasm or on the plant cell surface. NLR gene clusters have
recently gained momentum owing to their robustness and malleability in
adapting to recognize pathogens. The modular domain architecture of an NLR
provides valuable clues about its arms race with pathogens. Additionally, plant
NLRs have undergone functional specialization to have either one of the
following roles: to sense pathogen effectors (sensor NLRs) or co-ordinate
immune signaling (helper or executer NLRs). Sensor NLRs directly recognize
effectors whilst helper NLRs act as signaling hubs for more than one sensor NLR
to transduce the effector recognition into a successful plant immune response.
Furthermore, sensor NLRs can use guard, decoy, or integrated decoy models to
recognize effectors directly or indirectly. Thus, by studying a plant host’s NLR
repertoire, inferences can be made about a host’s evolutionary history and
defense potential which allows scientists to understand and exploit the
molecular basis of resistance in a plant host. This review provides a snapshot
of the structural and biochemical properties of the different classes of NLRs
which allow them to perceive pathogen effectors and contextualize these
findings by discussing the activation mechanisms of these NLR resistosomes
during plant defense. We also summarize future directives on applications of this
NLR structural biology. To our knowledge, this review is the first to collate all vast
defense properties of NLRs which make them valuable candidates for study in
applied plant biotechnology.
