Involvement of mitochondria and metacaspase elevation in harpin_Pss‐induced cell death of Saccharomyces cerevisiae

Abstract

Expression of a proteinaceous elicitor harpin Pss, encoded by hrpZ of Pseudomonas syringae pv. syringae 61, under GAL1 promoter in Saccharomyces cerevisiae Y187 resulted in galactose-inducible yeast cell death (YCD). Extracellular treatment of harpin did not affect the growth of yeast. The observed YCD was independent of the stage of cell cycle. ''Petite'' mutant of S. cerevisiae Y187 pYEUT-hrpZ was insensitive to cell death indicating the involvement of mitochondria in this YCD. Loss in mitochondrial potential, but no leakage of Cytochrome c from mitochondria into the cytosol, were notable features in harpin Pss -induced YCD. Cyclosporin A had no effect on hrpZ expressing yeast cells, further confirmed that there was no release of Cytochrome c. Elevation of caspase activity has been reported for the first time in this form of cell death induced by harpin expression. Release of reactive oxygen species and clear loss of membrane integrity were evident with the absence of nuclear fragmentation and chromosomal condensation, while annexin V and propidium iodide staining showed features typical of necrosis.

Molecular Characterization of Propolis-Induced Cell Death in Saccharomyces cerevisiae

“…However, it is not very clear, as it is in mammals, if cytochrome c release can lead to the formation of an apoptosome-like structure and activation of caspases. In contrast, Sripriya et al (77) have observed loss of mitochondrial membrane potential and absence of cytochrome c release during necrotic cell death of S. cerevisiae induced by expression of a proteinaceous elicitor hairpin (Pss) from Pseudomonas syringae. However, the deficiency of functional mitochondrial DNA, and consequent inability to respire from petite mutants, conferred resistance to death.…”

Necrosis in yeast

“…Death was avoided in ''petite'' mutants, which lack functional mitochondrial DNA and thus are unable to respire. In addition, a clear loss of membrane integrity with the absence of nuclear fragmentation or chromosomal condensation was evident [59].…”

“…Necrotic cell death of S. cerevisiae induced by expression of a proteinaceous elicitor harpin (Pss) from Pseudomonas syringae [59] occurred with loss of mitochondrial membrane potential but a lack of cytochrome c release. Death was avoided in ''petite'' mutants, which lack functional mitochondrial DNA and thus are unable to respire.…”

Metacaspases

“…17 Furthermore, metacaspase involvement in the yeast cell death models was investigated after in vivo staining for caspase activity by flow cytometry with FITC-labeled VAD-fmk (FITC-VAD-fmk). 17,[41][42][43][44] Likewise, in the fungus C. albicans, it was suggested that the antifungal compound Plagiochin E activated metacaspases based on the appearance of FITC-VAD-fmk labeled cells. 45 In the phytoplankton Chlamydomonas reinhardtii and other marine species, such as the diatom Thalassiosira pseudonana and the unicellular coccolithore Emiliania huxlei, increased caspase-like activity was correlated with increased accumulation of metacaspase mRNA and protein, thereby providing indirect evidence that metacaspases had caspase-like activity.…”