Autoimmunity in plants

Abstract

Attenuation in the activity of the negative regulators or the hyperactivity of plant innate immune receptors often causes ectopic defense activation manifested in severe growth retardation and spontaneous lesion formations, referred to as autoimmunity. In this review, we have described the cellular and molecular basis of the development of autoimmune responses for their useful applications in plant defense. Plants are exposed to diverse disease-causing pathogens, which bring infections by taking over the control on host immune machineries. To counter the challenges of evolving pathogenic races, plants recruit specific types of intracellular immune receptors that mostly belong to the family of polymorphic nucleotide-binding oligomerization domain-containing leucine-rich repeat (NLR) proteins. Upon recognition of effector molecules, NLR triggers hyperimmune signaling, which culminates in the form of a typical programmed cell death, designated hypersensitive response. Besides, few plant NLRs also guard certain host proteins known as 'guardee' that are modified by effector proteins. However, this fine-tuned innate immune system can be lopsided upon knock-out of the alleles that correspond to the host guardees, which mimick the presence of pathogen. The absence of pathogens causes inappropriate activation of the respective NLRs and results in the constitutive activation of plant defense and exhibiting autoimmunity. In plants, autoimmune mutants are readily scorable due to their dwarf phenotype and development of characteristic macroscopic disease lesions. Here, we summarize recent reports on autoimmune response in plants, how it is triggered, and phenotypic consequences associated with this phenomenon.

Plant NLRs with Integrated Domains: Unity Makes Strength

“…In animals, NLRs play a role in developmental processes, such as spermatogenesis and fertility, suggesting a control of the reproductive system by NLR proteins (Meunier and Broz, 2017). In plants, inappropriate activation of NLRs caused by mutations or incompatible combinations also impacts development (Chae et al, 2014;Chen et al, 2016;Atanasov et al, 2018;Chakraborty et al, 2018). The integrated decoy model predicts an important role of IDs in pathogen detection.…”

Type one protein phosphatases (TOPPs) contribute to the plant defense response in Arabidopsis

“…Considering these observations, we propose that some R proteins contribute to defense activation in topp4‐1 . Numerous studies have demonstrated that the autoimmune response is caused by excessive and improper activation of R proteins (Chakraborty et al ). Consequently, we speculate that autoimmunity in topp4‐1 is also a result of hyper‐activation of R proteins, and that high temperature recovers the immune‐related phenotype in topp4‐1 possibly through affecting the activation of R proteins.…”

The maize heterotrimeric G-protein β subunit controls shoot meristem development and immune responses

“…Thus, mutation of a 'guardee' may mimic the presence of a pathogen, and activate the guarding R protein, resulting in an autoimmune phenotype (47). It is therefore reasonable to speculate that grass Gb proteins function as immune guardees.…”