The C2 domain protein BAP1 negatively regulates defense responses in Arabidopsis.

The Arabidopsis BAP1 gene encodes a small protein with a C2-like domain. Here we show that the BAP1 protein is capable of binding to phospholipids in a calcium-dependent manner and is associated with membranes in vivo. We identify multiple roles of BAP1 in negatively regulating defense responses and cell death in Arabidopsis thaliana. The loss of BAP1 function confers an enhanced disease resistance to virulent bacterial and oomycete pathogens. The enhanced resistance is mediated by salicylic acid, PAD4 and a disease resistance gene SNC1. BAP1 is also involved in the control of cell death, which is suggested by an altered hypersensitive response to an avirulent bacterial pathogen in the bap1 loss-of-function mutant. BAP1 overexpression leads to an enhanced susceptibility to a virulent oomycete, suggesting a role for BAP1 in basal defense response. Furthermore, the BAP1 protein probably functions together with an evolutionarily conserved C2 domain protein BON1/CPN1 to negatively regulate defense responses in plants.