Reinventing the wheel with a synthetic plant inflammasome

Abstract

Both animal and plant cells rely on innate immune systems to recognize and appropriately respond to pathogens. These systems have many similar themes and surprising commonalities, both in the protein domains used and in the mechanisms of larger immune complexes (1). In PNAS, Duxbury et al. (2) explore these commonalities by generating functional plant–animal hybrid immune receptors to ask questions about how plant immune receptors function. In animals, the innate immune system is supported by adaptive immunity. Recombination of animal adaptive immune receptors greatly expands the ability of animals to recognize and respond to any pathogen (3). In contrast, plants lack adaptive immune cells: the innate immune system is on its own (1). The plant immune system must somehow be able to respond to all pathogens with an elaborated, but limited, set of genomically encoded receptors. So how do plants do it? Many details are still vague, but downstream of pathogen recognition, plant immune receptors activate both cell death and transcriptional outputs to promote defense. Despite their agronomic significance, and over 25 y of study, how plant immune receptors are able to activate defense responses remains a mystery (4, 5). Propelled by the introduction of plant molecular biology in the 1980–90s and the sequencing of the first plant genome in 2001, researchers realized that plants share just a few common types of immune receptors to monitor the outside and inside of cells (6). One major class, the nucleotide-binding site, leucine-rich repeat (“NBS-LRR,” or simply “NLR”) proteins, detects intracellular signals of pathogens. This class of receptors was named for its stereotypical domains: a N-terminal coiled-coil (CC/CCR) or Toll–interleukin-1 receptor (TIR) domain, a central nucleotide binding site domain (NBS), and a C-terminal leucine-rich repeat (LRR) (6). Plant genomes typically have hundreds of these proteins, and they can detect pathogens … [↵][1]1To whom correspondence may be addressed. Email: marcusn{at}colostate.edu. [1]: #xref-corresp-1-1