Constitutive Negative Regulation of R Proteins in Arabidopsis also via Autophagy Related Pathway?

Abstract

Even though resistance (R) genes are among the most studied components of the plant immunity, there remain still a lot of aspects to be explained about the regulation of their function. Many gain-of-function mutants of R genes and loss-of-function of their regulators often demonstrate up-regulated defense responses in combination with dwarf stature and/or spontaneous leaf lesions formation. For most of these mutants, phenotypes are a consequence of an ectopic activation of R genes. Based on the compilation and comparison of published results in this field, we have concluded that the constitutively activated defense phenotypes recurrently arise by disruption of tight, constitutive and multilevel negative control of some of R proteins that might involve also their targeting to the autophagy pathway. This mode of R protein regulation is supported also by protein–protein interactions listed in available databases, as well as in silico search for autophagy machinery interacting motifs. The suggested model could resolve some explanatory discrepancies found in the studies of the immunity responses of autophagy mutants.

Growth–defense trade‐offs and yield loss in plants with engineered cell walls

“…Components of the plant immune system participate in complex responses including pathogen detection and signal transduction that evoke various defense‐related responses, and R genes play an important role as central components. Components of the plant immune response, including R genes, are tightly controlled by negative regulators at various checkpoints to maintain immune homeostasis, since failure to regulate the immune machineries would result in unnecessary constitutive expression of defense genes (Pecenkova et al ., 2016; van Wersch et al ., 2016; Chakraborty et al ., 2018). Therefore, signaling from R genes in wild‐type plants remains inactive in the absence of invading pathogens.…”

“…Therefore, signaling from R genes in wild‐type plants remains inactive in the absence of invading pathogens. However, gain‐of‐function mutants of R genes and loss‐of‐function of their negative regulators lead to ectopic expression of R genes and ectopic defense activation, resulting in appearance of autoimmunity (Pecenkova et al ., 2016; van Wersch et al ., 2016; Chakraborty et al ., 2018).…”

“…Autoimmune plant mutants show dwarfism, seedling lethality and spontaneous lesion formation as visible phenotypes, and accumulation of SA as a molecular phenotype (Pecenkova et al ., 2016; van Wersch et al ., 2016; Chakraborty et al ., 2018). Moreover, autoimmune mutants show enhanced expression of a range of downstream defense‐related genes including PR genes, suggesting a connection between appearance of the dwarf phenotype and increased expression of such genes (Table 2).…”

Tethering Complexes in the Arabidopsis Endomembrane System

“…TN2 is proposed to function as a sentinel monitoring EXO70B1 integrity (Zhao et al, 2015 ). An alternative scenario was proposed recently—that autophagy processes (involving also EXO70B1) might be in some cases involved in the down regulation of plant nucleotide binding domain and leucine-rich repeat-containing (NLR)-like disease resistance (R) proteins (Pečenková et al, 2016 ). Also, exocyst core subunits are implicated in the warfare between plants and pathogens, since the Phytophthora infestans effector avirulence factor 1 (AVR1) specifically targets exocyst subunit SEC5 in potato (Du et al, 2015 ).…”

OsExo70B1 Positively Regulates Disease Resistance to Magnaporthe oryzae in Rice

“…EXPO is uniquely labeled by components of the exocyst complex, an evolutionarily conserved octameric tethering factor, which mediates post Golgi vesicle fusion with the plasma membrane (PM) and plays a major role in exocytosis [ 7 , 8 , 9 , 10 , 11 ]. The exocyst complex consists of eight subunits: Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70 and Exo84 [ 12 ].…”