AtBI-1, a plant homologue of Bax Inhibitor-1, suppresses Bax-induced cell death in yeast and is rapidly upregulated during wounding and pathogen challenge

Extensive searches have so far failed to identify functional plant homologu es of the mammalian apoptotic machinery. Here we report the isolation and c haracterisation of an Arabidopsis thaliana homologue of human Bax Inhibitor -1, AtBI-1, isolated during a differential screen of plants challenged with the phytopathogen Pseudomonas syringae. AtBI is a member of a small gene f amily in Arabidopsis, members of which display extensive amino acid identit y to human BI-1. AtBI-1 is also functionally similar to BI-1 in its ability to suppress the lethal phenotype in yeast conferred by expression of the m ammalian proapoptotic protein, Bax. Expression of AtBI-1 is rapidly upregul ated in plants during wounding or pathogen challenge, suggesting a role in responses to biotic and abiotic stress. AtBI-1 upregulation appears R gene independent and is not markedly affected by mutations required for specific classes of R genes. However, the accumulation of AtBI-1 message is signifi cantly reduced in coi1, in which defence responses to insects, pathogens an d wounding are compromised.