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

Abstract

Extensive searches have so far failed to identify functional plant homologues of the mammalian apoptotic machinery. Here we report the isolation and characterisation of an Arabidopsis thaliana homologue of human Bax Inhibitor-1, AtBl-1, isolated during a differential screen of plants challenged with the phytopathogen Pseudomonas syringae. AtBl is a member of a small gene family in Arabidopsis, members of which display extensive amino acid identity to human Bl-1. AtBl-1 is also functionally similar to Bl-1 in its ability to suppress the lethal phenotype in yeast conferred by expression of the mammalian proapoptotic protein, Bax. Expression of AtBl-1 is rapidly upregulated 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 AtBl-1 message is significantly reduced in coi1, in which defence responses to insects, pathogens and wounding are compromised.