Abstract
Cell death suppressor Bax inhibitor-1 (BI-1), an endoplasmic reticulum membrane protein, exists in a wide range of organisms. The split-ubiquitin system, overlay assay, and bimolecular fluorescence complementation analysis demonstrated that Arabidopsis (Arabidopsis thaliana) BI-1 (AtBI-1) interacted with calmodulin in yeast (Saccharomyces cerevisiae) and in plant cells. Furthermore, AtBI-1 failed to rescue yeast mutants lacking Ca2+ ATPase (Pmr1 or Spf1) from Bax-induced cell death. Pmr1 and Spf1, p-type ATPases localized at the inner membrane, are believed to be involved in transmembrane movement of calcium ions in yeast. Thus, the presence of intact Ca2+ ATPases was essential for AtBI-1-mediated cell death suppression in yeast. To investigate the effect of AtBI-1 on calcium homeostasis, we evaluated sensitivity against cyclopiazonic acid (CPA), an inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase in AtBI-1-overexpressing or knock-down transgenic Arabidopsis plants. These plants demonstrated altered CPA or ion stress sensitivity. Furthermore, AtBI-1-overexpressing cells demonstrated an attenuated rise in cytosolic calcium following CPA or H2O2 treatment, suggesting that AtBI-1 affects ion homeostasis in plant cell death regulation.
Highlights
Cell death suppressor Bax inhibitor-1 (BI-1), an endoplasmic reticulum membrane protein, exists in a wide range of organisms
To understand the relationship between intracellular calcium homeostasis and BI-1 in plant cells, we evaluated the effect of cyclopiazonic acid (CPA), a specific inhibitor of sarcoplasmic/ endoplasmic reticulum Ca21 ATPase (SERCA), using transgenic Arabidopsis plants with AtBI-1 overexpression (OX) or knock-down (KD) lines (Fig. 5A)
Evidence from previous studies suggests that such Ca21 fluxes trigger various cellular responses, such as microtubule depolymerization, defense gene activation, and cell death (Lecourieux et al, 2002)
Summary
Cell death suppressor Bax inhibitor-1 (BI-1), an endoplasmic reticulum membrane protein, exists in a wide range of organisms. To investigate the effect of AtBI-1 on calcium homeostasis, we evaluated sensitivity against cyclopiazonic acid (CPA), an inhibitor of sarcoplasmic/endoplasmic reticulum Ca21 ATPase in AtBI-1-overexpressing or knock-down transgenic Arabidopsis plants. These plants demonstrated altered CPA or ion stress sensitivity. Overexpression of Arabidopsis (Arabidopsis thaliana) BI-1 (AtBI-1) suppresses Bax-induced cell death in Arabidopsis and yeast (Kawai et al, 1999; Sanchez et al, 2000; Kawai-Yamada et al, 2001, 2004). H2O2-, salicylic acid (SA)-, elicitor-, heat-, and cold-induced cell death were suppressed in plant cells overexpressing AtBI-1 (Chae et al, 2003; Matsumura et al, 2003; Kawai-Yamada et al, 2004). The mechanism of BI-1-mediated suppression of cell death is still unclear
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