A chemical screen for suppressors of the avrRpm1-RPM1-dependent hypersensitive cell death response in Arabidopsis thaliana.
Arabidopsis thaliana RPM1 encodes an intracellular immune sensor that conditions disease resistance to Pseudomonas syringae expressing the type III effector protein AvrRpm1. Conditional expression of this type III effector in a transgenic line carrying avrRpm1 under the control of a steroid-inducible promoter results in RPM1-dependent cell death that resembles the cell death response of the incompatible RPM1-avrRpm1 plant-bacterium interaction. This line was previously used in a genetic screen, which revealed two genes that likely function in the folding of pre-activation RPM1. We established a chemical screen for small molecules that suppress steroid-inducible and RPM1-avrRpm1-dependent cell death in Arabidopsis seedlings. Screening of a library comprising 6,800 compounds of natural origin identified two trichothecene-type mycotoxins, 4,15-diacetoxyscirpenol (DAS) and neosolaniol (NEO), which are synthesized by Fusarium and other fungal species. However, protein blot analysis revealed that DAS and NEO inhibit AvrRpm1 synthesis rather than suppress RPM1-mediated responses. This inhibition of translational activity likely explains the survival of the seedlings under screening conditions. Likewise, flg22-induced defense responses are also impaired at the translational, but not the transcriptional, level by DAS or NEO. Unexpectedly, both compounds not only prevented AvrRpm1 synthesis, but rather caused an apparent hyper-accumulation of RPM1 and HSP70. The hyper-accumulation phenotype is likely unrelated to the ribotoxic function of DAS and NEO and could be due to an inhibitory activity on the proteolytic machinery of Arabidopsis or elicitor-like activities of type A trichothecenes.
Department of Plant-Microbe Interactions, Max Planck Institute for Plant Breeding Research, Cologne, Germany.
Mario
M
Serrano
David A
DA
Hubert
Jeffery L
JL
Dangl
Paul
P
Schulze-Lefert
Erich
E
Kombrink
D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000276:immunology / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D005670:Fusarium / Q000737:chemistry; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006576:Heterocyclic Compounds, 4 or More Rings / Q000737:chemistry / Q000494:pharmacology; D009183:Mycotoxins / Q000737:chemistry / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000032:analysis / Q000737:chemistry / Q000494:pharmacology; D054852:Small Molecule Libraries / Q000032:analysis* / Q000494:pharmacology*; D014255:Trichothecenes / Q000737:chemistry / Q000494:pharmacology
C506431:4,15-diacetoxyscirpenol; D029681:Arabidopsis Proteins; C502082:AvrRpm1 protein, Pseudomonas syringae; D001426:Bacterial Proteins; D006576:Heterocyclic Compounds, 4 or More Rings; D009183:Mycotoxins; D011500:Protein Synthesis Inhibitors; C095014:RPM1 protein, Arabidopsis; D054852:Small Molecule Libraries; D014255:Trichothecenes; C016009:neosolaniol