Abstract
Poly(ADP-ribosyl)ation is a posttranslational protein modification in which ADP-ribose (ADP-Rib) units derived from NAD(+) are attached to proteins by poly(ADP-Rib) polymerase (PARP) enzymes. ADP-Rib groups are removed from these polymer chains by the enzyme poly(ADP-Rib) glycohydrolase (PARG). In animals, poly(ADP-ribosyl)ation is associated with DNA damage responses and programmed cell death. Previously, we hypothesized a role for poly(ADP-ribosyl)ation in plant defense responses when we detected defense-associated expression of the poly(ADP-ribosyl)ation-related genes PARG2 and NUDT7 and observed altered callose deposition in the presence of a chemical PARP inhibitor. The role of poly(ADP-ribosyl)ation in plant defenses was more extensively investigated in this study, using Arabidopsis (Arabidopsis thaliana). Pharmacological inhibition of PARP using 3-aminobenzamide perturbs certain innate immune responses to microbe-associated molecular patterns (flg22 and elf18), including callose deposition, lignin deposition, pigment accumulation, and phenylalanine ammonia lyase activity, but does not disrupt other responses, such as the initial oxidative burst and expression of some early defense-associated genes. Mutant parg1 seedlings exhibit exaggerated seedling growth inhibition and pigment accumulation in response to elf18 and are hypersensitive to the DNA-damaging agent mitomycin C. Both parg1 and parg2 knockout plants show accelerated onset of disease symptoms when infected with Botrytis cinerea. Cellular levels of ADP-Rib polymer increase after infection with avirulent Pseudomonas syringae pv tomato DC3000 avrRpt2(+), and pathogen-dependent changes in the poly(ADP-ribosyl)ation of discrete proteins were also observed. We conclude that poly(ADP-ribosyl)ation is a functional component in plant responses to biotic stress.
Highlights
Poly(ADP-ribosyl)ation is a posttranslational protein modification in which ADP-ribose (ADP-Rib) units derived from NAD+ are attached to proteins by poly(ADP-Rib) polymerase (PARP) enzymes
We discovered that treatment with the PARP inhibitor 3AB does not block wound-induced callose deposition, nor does it reduce the constitutively active callose observed in mekk12 mutants (Suarez-Rodriguez et al, 2007; Fig. 1A), indicating that 3AB blocks microbe-associated molecular patterns (MAMPs)-induced callose deposition
To investigate where in the pathway of basal immune signaling 3AB might be acting to disrupt callose deposition, we examined the impact of PARP inhibition on MAMP-elicited production of reactive oxygen species (ROS) and induction of two MAMP-induced genes, WRKY29 and FRK1, that are normally expressed within 30 min of MAMP treatment (Asai et al, 2002)
Summary
Poly(ADP-ribosyl)ation is a posttranslational protein modification in which ADP-ribose (ADP-Rib) units derived from NAD+ are attached to proteins by poly(ADP-Rib) polymerase (PARP) enzymes. We found that pharmacological inhibition of poly(ADP-Rib) polymerase (PARP) blocked the formation of callosecontaining cell wall depositions induced by the MAMPs flg and elf (Adams-Phillips et al, 2008). This suggested a role for poly(ADP-ribosyl)ation in the pathways that regulate pathogen-elicited callose deposition and plant innate immune responses
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