Autophagic Components Contribute to Hypersensitive Cell Death in Arabidopsis

Abstract

SUMMARYAutophagy has been implicated as a prosurvival mechanism to restrict programmed cell death (PCD) associated with the pathogen-triggered hypersensitive response (HR) during plant innate immunity. This model is based on the observation that HR lesions spread in plants with reduced autophagy gene expression. Here, we examined receptor-mediated HR PCD responses in autophagy-deficient Arabidopsis knockout mutants (atg), and show that infectioninduced lesions are contained in atg mutants. We also provide evidence that HR cell death initiated via Toll/Interleukin-1 (TIR)-type immune receptors through the defense regulator EDS1 is suppressed in atg mutants. Furthermore, we demonstrate that PCD triggered by coiled-coil (CC)-type immune receptors via NDR1 is either autophagy-independent or engages autophagic components with cathepsins and other unidentified cell death mediators. Thus, autophagic cell death contributes to HR PCD and can function in parallel with other prodeath pathways.

Do plastids inDendrobiumcv. Lucky Duan petals function similar to autophagosomes and autolysosomes?

“…A pathogen-induced PCD was delayed by knocking out ATG genes. 44 The present data suggest evidence for processes similar to macroautophagy, carried out by plastids. Plastids with intraplastidial spaces were observed in cells that were physiologically still young (having a small vacuolar volume), in older cells, and in cells that were close to death.…”

Role of plant autophagy in stress response

“…However, Hofius et al discovered that autophagy may contribute to HRprogrammed cell death (PCD) in a pro-death way. The Arabidopsis knockout atg mutants atg7 and atg9 show delayed PCD induced by the avirulent bacterial strain Pto AvrRPS4 or the avirulent isolate Noco2 of the phytopathogenic oomycete Hyaloperonospora arabidopsidis (Hofius et al, 2009). Furthermore, the contribution of autophagy to cell death execution in plant R gene-mediated resistance is dependent on the type of resistance receptors.…”

“…Furthermore, the contribution of autophagy to cell death execution in plant R gene-mediated resistance is dependent on the type of resistance receptors. CC-NBS-LRR receptors trigger cell death that is partially (RPM1) dependent on or independent (RPS2) of autophagy, whereas TIR-NBS-LRR receptors (RPS4 and RPP1) are strictly dependent on autophagy (Hofius et al, 2009). Yoshimoto et al proposed an explanation for such apparent controversial observations based on their independent experiment .…”

“…Thus, they proposed that autophagy negatively regulates cell death by NPR1-dependent SA signaling during senescence and innate immune response . Interestingly, despite that autophagy-defective plants accumulate higher level of SA, these plants support increased growth of the incompatible pathogens including virus and bacteria (Liu et al, 2005;Hofius et al, 2009). More bacteria may secrete more effectors that may suppress HR, a form of PCD.…”

“…Arabidopsis ATG7 knockout mutants and ATG6 RNAi plants reportedly support the increased growth of the virulent hemibiotrophic pathogen Pst DC3000 (Patel and Dinesh-Kumar, 2008;Hofius et al, 2009). However, these observations obviously contradict the recent report that three Arabidopsis mutant lines, Atatg5, atg10, and atg18a, showed an enhanced resistance towards the same virulent pathogen Pst DC3000 (Lenz et al, 2011).…”