title: Heat shock protein 70 is required for tabtoxinine-β-lactam-induced cell death in Nicotiana benthamiana.
abstract: Tabtoxinine-β-lactam (TβL), a non-specific bacterial toxin, is produced by Pseudomonas syringae pv. tabaci, the causal agent of tobacco wildfire disease. TβL causes death of plant cells through the inhibition of glutamine synthetase, which leads to an abnormal accumulation of ammonium ions and the characteristic necrotic wildfire lesions. To better understand the mechanisms involved in TβL-induced cell death, we studied its regulation in Nicotiana benthamiana. TβL-induced lesions, similar to those in controls, could be observed in SGT1-, RAR1- and Hsp90-silenced plants. In contrast, Hsp70-silenced plants showed suppression of lesion formation. Expression of hin1, a marker gene for the hypersensitive response (HR), which is a characteristic of programmed cell death in plants, was strongly induced in controls by TβL treatment but only slightly in Hsp70-silenced plants. However, in these TβL-treated Hsp70-silenced plants, the amount of ammonium ions was considerably increased. Furthermore, the silencing of Hsp70 also suppressed l-methionine sulfoximine-induced cell death and hin1 expression and caused the over-accumulation of ammonium ions. When inoculated directly with P. syringae pv. tabaci, Hsp70-silenced plants showed only reduced symptoms. Our results suggest that the TβL-induced pathway to cell death in N. benthamiana is at least partially similar to HR response, and that Hsp70 might play an essential role in these events.
authors: Laboratory of Plant Pathology and Biotechnology, Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan.
authors: Makoto
authors: M
authors: Ito
authors: Laboratory of Bioactive Substance Chemistry, Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan.
authors: Yu
authors: Y
authors: Yamamoto
authors: Laboratory of Bioactive Substance Chemistry, Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan.
authors: Chul-Sa
authors: CS
authors: Kim
authors: Research Institute of Molecular Genetics, Kochi University, Nankoku 783-8502, Japan.
authors: Kouhei
authors: K
authors: Ohnishi
authors: Laboratory of Plant Pathology and Biotechnology, Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan.
authors: Yasufumi
authors: Y
authors: Hikichi
authors: Laboratory of Plant Pathology and Biotechnology, Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan. Electronic address: akiba@kochi-u.ac.jp.
authors: Akinori
authors: A
authors: Kiba
mesh_terms: D001384:Azetidines / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000494:pharmacology*; D016923:Cell Death; D020868:Gene Silencing; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology*; D008717:Methionine Sulfoximine; D010935:Plant Diseases; D014026:Nicotiana / Q000382:microbiology*
chemical_list: D001384:Azetidines; D001427:Bacterial Toxins; D018840:HSP70 Heat-Shock Proteins; D008717:Methionine Sulfoximine; C051368:tabtoxinine beta-lactam; D005974:Glutamate-Ammonia Ligase
keywords: Cell death; HR; Heat shock protein 70; Hsp; MSX; Nicotiana benthamiana; PCD; PCR; RT-PCR; Tabtoxinine-β-lactam; TβL; VIGS; Virus-induced gene silencing; heat shock protein; hypersensitive response; l-methionine sulfoximine; polymerase chain reaction; programmed cell death; qRT-PCR; quantitative real time polymerase chain reaction; reverse transcription-polymerase chain reaction; tabtoxinine-β-lactam; virus-induced gene silencing