The Peptaibol Alamethicin Induces an rRNA‐Cleavage‐Associated Death in Arabidopsis thaliana

Abstract

The plant-metabolic response to amphipathic peptides produced by the soil fungi of the genus Trichoderma remains largely unknown. The present investigation was undertaken to examine the death process in alamethicin-treated Arabidopsis thaliana plantlets. The rapid death triggered by alamethicin (at 50 microM) was shown to be associated with protein-synthesis arrest and with specific cleavage of 18S and 25S ribosomal RNA. The use of an inhibitor of nitric oxide (NO) synthases and of an NO scavenger suggested that rRNA cleavage was suppressed by NO. Experiments conducted with a synthetic alamethicin analogue, in which all alpha-aminoisobutyric acid (Aib) residues have been replaced by leucine moieties, showed that the non-coded residues are essential for the ability of the peptaibol to induce rRNA cleavage in Arabidopsis. Our data indicate that further investigations on the mode of action of alamethicin in planta could be of great interest to study the death-signaling pathway associated with rRNA degradation in plants.

Hypersensitive‐Like Response to the Pore‐Former Peptaibol Alamethicin in Arabidopsis Thaliana

“…It has previously been shown that specific cleavage of rRNA occurs among the events that are associated with plantlet death under these conditions. [34] rRNA cleavage was not observed in plants challenged by Alm at lower concentrations. Thus, the death processes that are involved in the A. thaliana defense-like response to Alm at low doses and in the rRNA cleavage-associated death at higher concentrations were associated with different active cellular events.…”

“…Moreover, Mel has been shown to be more sensitive than Alm to the proteolytic activity of an Arabidopsis cell extract. [34] The HR-like elicitation and systemic response observed with Alm could be related to a more significant enzymatic stability of the peptaibol in planta due to its high content (37 %) in Aib residues. [42][43][44][45][46][47] The other peptides investigated in this work included the natural peptaibol AmpA, (Leu12-OMe)cervinin, and a set of synthetic lipopeptaibols comprising seven to 19 amino acid residues and bearing a methyl ester at the C terminus and an 1-octanoyl group at the N terminus.…”

“…thaliana ecotype Col-0 plants were grown as previously described. [34] Briefly, plants were grown at 24 8C under long-day conditions (16 h light cycle at 100 mE m À2 s À1 illumination). For aseptic growth, seeds were surface sterilized and germinated under sterile conditions on half-strength MS salt plates.…”

“…Plantlets were challenged by using "moderate" concentrations of Alm, as this peptide is toxic when supplied at high concentrations under similar experimental conditions. [34] Plantlets were observed seven days after their transfer to a growth medium supplemented with 5 mm peptide. Alm induced macroscopic lesions on leaves ( [32] were of similar intensities.…”

Recent Results in Alamethicin Research

“…Based on their results, the authors suggested that a specific stimulus activates RNases which leads to the cleavage of cytosolic and chloroplastic rRNA molecules at specific sites. Experiments conducted with ALM-dUL, a synthetic ALM analogue in which all Aib residues are replaced by leucine moieties, showed that the Aib residues are essential for the induction of rRNA cleavage and triggering plant death [73]. In a subsequent study [74], thaliana increased with the peptaibol's membrane permeabilization ability and was strongly associated with α-aminoisobutyric acid content.…”