Antagonistic action of harpin proteins: HrpWea from Erwinia amylovora suppresses HrpNea-induced cell death in Arabidopsis thaliana

Abstract

Harpins are proteins secreted by the type-three secretion system of phytopathogenic bacteria. They are known to induce a hypersensitive response (HR) in non-host plant leaf tissue. Erwinia amylovora, the fire blight pathogen of pear and apple trees, secretes two different harpins, HrpNea and HrpWea. In the present study, we showed that an Erwinia amylovora hrpWea mutant induces stronger electrolyte leakages in Arabidopsis thaliana foliar disks than the wild-type strain, thus suggesting that HrpWea could function as a HR negative modulator. We confirmed this result by using purified HrpWea and HrpNea. HrpWea has dual effects depending on its concentration. At 200 nM, HrpWea, like HrpNea, provoked the classical defense response – active oxygen species (AOS) production and cell death. However, at 0.2 nM, HrpWea inhibited cell death and AOS production provoked by HrpNea. HrpWea probably inhibits HrpNea-induced cell death by preventing anion channel inhibition, confirming that anion channel regulation is a determinant feature of the plant response to harpins. Collectively our data show that the HrpWea harpin can act antagonistically to the classical HrpNea harpin by suppressing plant defense mechanisms.

Two different signaling pathways for thaxtomin A-induced cell death in Arabidopsis and tobacco BY2

“…10 We recently reported new insights regarding the effect of TXT 11 by using A. thaliana suspension cells, a convenient material for studying early physiological events induced by pathogens. 10,[12][13][14][15] We showed that the transient increase in [Ca 2+ ] cyt was a key step of a further signaling pathway leading to the death of the cells in response to a TXT accordingly to previous studies which showed that Ca 2+ activity changes are involved in PCD in plant, as in animal. 16,17 Fast rises in [Ca 2+ ] cyt are effectively also frequently described as one of the earliest responses to various microbial phytotoxins and elicitors 18,19 and numerous studies led to the conclusion that activation of defence responses depends on Ca 2+ influxes from the apoplast into the cytosol of plant cells.…”

Early events induced by the toxin deoxynivalenol lead to programmed cell death in Nicotiana tabacum cells

“…Cell viability was assessed using the fluorescein diacetate (FDA) spectrofluorimetric method [18]. After the appropriate DONtreatment, 1 ml of cell suspension (0.05 g FW) was gently stirred with a magnetic stirrer before FDA was added at a final concentration of 12 M. The fluorescence increase was monitored over 120 s using an F-2000 spectrofluorimeter (Hitachi, Japan).…”

Prevention of Copper-Induced Calcium Influx and Cell Death by Prion-Derived Peptide in Suspension-Cultured Tobacco Cells

“…Harpins are typical for such proteins which are heat-stable, glycine-rich type III secreted proteins produced by Gram-negative plant pathogenic bacteria such as Erwinia amylovora (secretion mechanisms are widely preserved), that cause a hypersensitive response when applied to the cells of tobacco (Wei et al, 1992;Galan and Collmer, 1999), and Arabidopsis thaliana (Reboutier et al, 2005(Reboutier et al, , 2007, possibly through regulation of ion channels (El-Maarouf et al, 2001). Recent studies have pointed out that harpin proteins (particularly the motif 2 region) that interact with host plant cells have great similarity with PrP in their capability of fi bril formation (Oh et al, 2007;Resende et al, 2003) and in the structure (highly homologous to the prionforming domain within the yeast prion protein Rnq1p).…”