Abstract
Here we identify the BAP1 and BAP2 genes of Arabidopsis (Arabidopsis thaliana) as general inhibitors of programmed cell death (PCD) across the kingdoms. These two homologous genes encode small proteins containing a calcium-dependent phospholipid-binding C2 domain. BAP1 and its functional partner BON1 have been shown to negatively regulate defense responses and a disease resistance gene SNC1. Genetic studies here reveal an overlapping function of the BAP1 and BAP2 genes in cell death control. The loss of BAP2 function induces accelerated hypersensitive responses but does not compromise plant growth or confer enhanced resistance to virulent bacterial or oomycete pathogens. The loss of both BAP1 and BAP2 confers seedling lethality mediated by PAD4 and EDS1, two regulators of cell death and defense responses. Overexpression of BAP1 or BAP2 with their partner BON1 inhibits PCD induced by pathogens, the proapoptotic gene BAX, and superoxide-generating paraquat in Arabidopsis or Nicotiana benthamiana. Moreover, expressing BAP1 or BAP2 in yeast (Saccharomyces cerevisiae) alleviates cell death induced by hydrogen peroxide. Thus, the BAP genes function as general negative regulators of PCD induced by biotic and abiotic stimuli including reactive oxygen species. The dual roles of BAP and BON genes in repressing defense responses mediated by disease resistance genes and in inhibiting general PCD has implications in understanding the evolution of plant innate immunity.
Highlights
We identify the BAP1 and BAP2 genes of Arabidopsis (Arabidopsis thaliana) as general inhibitors of programmed cell death (PCD) across the kingdoms
ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), PHYTOALEXIN DEFICIENT4 (PAD4), and NONRACE-SPECIFIC DISEASE RESISTANCE1 (NDR1) are implicated in the amplification of cell death and this function appears to be independent from their roles in R-gene-mediated defense responses (Clarke et al, 2001; Rusterucci et al, 2001)
Using reverse transcription-PCR, we isolated a cDNA of BAP2 and found that it encodes a small protein of 207 amino acids containing a C2 domain at the amino
Summary
We identify the BAP1 and BAP2 genes of Arabidopsis (Arabidopsis thaliana) as general inhibitors of programmed cell death (PCD) across the kingdoms. The loss of BAP2 function induces accelerated hypersensitive responses but does not compromise plant growth or confer enhanced resistance to virulent bacterial or oomycete pathogens The loss of both BAP1 and BAP2 confers seedling lethality mediated by PAD4 and EDS1, two regulators of cell death and defense responses. The dual roles of BAP and BON genes in repressing defense responses mediated by disease resistance genes and in inhibiting general PCD has implications in understanding the evolution of plant innate immunity. About half a dozen mutants, including some lsd and acd, are unable to control the rate and extent of lesions and form chlorosis in a large area (Lorrain et al, 2003) Most of these lesion mimic mutants have altered defense responses, further indicating an intricate connection between cell death and disease resistance. Understanding how each individual gene modulates cell death is essential to deciphering cell death control and defense pathways
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