We identified genes based on screening of an Arabidopsis cDNA library for functional suppressors of mouse Bax-induced cell death of yeast cells. Interestingly, the cDNA encoding AtEBP, known as Arabidopsis thaliana ethyleneresponsive element binding protein, was isolated numerous times in the functional screen (82% of all suppressors). Full-length AtEBP and its localization to the nucleus were essential for the suppression of Bax-induced cell death. Morphological abnormality of intracellular network that is a hallmark of Bax-induced cell death was attenuated by expression of AtEBP. ß

Overexpression of the mammalian proapoptotic protein Bax induces cell death in plant and yeast cells. The Bax inihibitor-1 (BI-1) gene rescues yeast and plant from Bax-mediated lethality. Using the Arabidopsis BI-1 (AtBI-1) gene controlled by the GAL1 promoter as a cell death suppressor in yeast, Cdf1 (cell growth defect factor-1) was isolated from Arabidopsis cDNA library. Overexpression of Cdf1 caused cell death in yeast, whereas such an effect was suppressed by co-expression of AtBI-1. The Cdf1 protein fused with a green fluorescent protein was localized in the mitochondria and resulted in the loss of mitochondrial membrane potential in yeast. The Bax-resistant mutant BRM1 demonstrated tolerance against Cdf1-mediated lethality, whereas the ⌬atp4 strain was sensitive to Cdf1. Our results suggest that Cdf1 and Bax cause mitochondria-mediated yeast lethality through partially overlapped pathways.Proteins encoded by Bcl-2 family interact with each other and either promote or inhibit metazoan apoptosis. A basic local alignment search tool (BLAST) data base search of the Arabidopsis thaliana genome showed no obvious homologues of any crucial regulator of metazoan apoptosis (members of the Bcl-2 family, p53, etc.) (1, 2). However, it has been demonstrated that mammalian proapoptotic proteins can kill plant (3, 4) as well as yeast (5-9). Furthermore, the antiapoptotic proteins Bcl-XL, Bcl-2, and Ced9 protect tobacco plants against cell death induced by ultraviolet light irradiation, paraquat treatment, hypersensitive response upon tobacco mosaic virus infection, and fungal pathogens (10, 11). The Pseudomonas AvrPtoB effecter protein, conserved among diverse genera of plant pathogens, acts to inhibit Bax-induced cell death (12). This evidence clearly suggests that some mechanisms of cell death are evolutionarily conserved throughout the metazoa and plants.In yeast, cell death with apoptosis-like features has also been reported after treatment with acetic acid, UV light irradiation, and H 2 O 2 (reviewed in Ref. 13). Madeo et al. (14) reported that a caspase-like gene (Yor197w) identified in Saccharomyces cerevisiae was implicated in cell death induced by H 2 O 2 , acetic acid, and aging. Yeast cells undergoing Bax-induced death exhibit ultrastructural changes that include massive cytosolic vacuolation and apparent disruption of mitochondria (6,8).Classical yeast genetic approaches have been successfully applied for identification of genes related to the regulation of mammalian apoptosis. Even though the yeast genome lacks some of the molecular machinery responsible for apoptosis in metazoans, it can be powerful tool in the isolation of apoptosis-related genes.The Bax inhibitor-1 (BI-1) 2 gene of Arabidopsis (AtBI-1) and the Oryza sativa Bax inhibitor-1 gene (OsBI-1), which are plant homologues of mammalian antiapoptotic gene BI-1, were isolated as suppressors of Bax-mediated lethality in yeast (15)(16)(17)(18)(19). Mammalian BI-1 suppresses apoptosis induced by Bax, etoposide, staurosporine, and growth factor depriva...

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