The BON/CPN gene family represses cell death and promotes cell growth in Arabidopsis

Abstract

SummaryCopines are calcium-dependent membrane-binding proteins that are highly conserved among protozoa, plants, nematodes and mammals. Although they are implicated in membrane trafficking and signal transduction, the functions of these proteins are not well understood. The Arabidopsis copine gene BON1/ CPN1 was previously shown to negatively regulate a disease resistance (R) gene SNC1. Here we report that in Arabidopsis, as in other organisms, there is a family of copine genes, BON1, 2 and 3. Using double and triple mutant combinations we show that these three copine genes have overlapping functions essential for the viability of plants. The loss of function of BON1 combined with that of BON2 or BON3 leads to extensive cell death phenotypes resembling the hypersensitive response (HR) in defense responses. The resulting lethality can be suppressed by mutations in PAD4 or EDS1 which are required for R gene signaling and cell death control. Accession-dependent phenotypes of the mutant combinations suggest that the BON/CPN genes may together repress several R genes other than SNC1. Moreover, the mutant combinations exhibit developmental defects when R-gene-mediated defense responses are largely suppressed in pad4 and eds1 mutants. Thus, the copine family in Arabidopsis may have effects in promoting growth and development in addition to repressing cell death, and these two processes might be intricately intertwined.

The ArabidopsisBAP1andBAP2Genes Are General Inhibitors of Programmed Cell Death

“…None of the wildtype Col leaves (0/8) analyzed had any staining, neither did the bap1 (0/8) or the bap2 (0/8) single mutants. Strong staining was found in most of the leaves of bon1-1 (9/ 14), consistent with previous findings (Jambunathan et al, 2001;Yang et al, 2006b). Very few leaves of bap1/1bap2 (1/8) were stained by trypan blue, while most of the bap1bap2/1 leaves (7/12) were stained.…”

“…Because BON2 and BON3 have overlapping functions with BON1 (Yang et al, 2006b), we further determined whether BAP1 and BAP2 can interact with BON2 or BON3 in the yeast two-hybrid system. Coexpression of GBD:BAP1 or GBD:BAP2 with GAD: BON2A and GAD:BON3A, respectively, conferred yeast growth on the selection medium (Fig.…”

“…Overexpression of BAP1 confers wild-type plants an enhanced susceptibility to a virulent oomycete in a SNC1-independent manner (Yang et al, 2006a). Furthermore, the loss of function of all BON1 family (BON1, BON2, BON3) results in seedling lethality that is largely suppressed by eds1, pad4, but not by snc1 or nahG (Yang et al, 2006b). Thus, BON1 has an overlapping function with its two homologs in Arabidopsis and their shared function is not totally SNC1 dependent.…”

MEKK1 Is Required for flg22-Induced MPK4 Activation in Arabidopsis Plants

“…A similar situation has been previously described for the Arabidopsis humidity-and temperature-sensitive mutant BONZAI1 (Hua et al, 2001;Jambunathan et al, 2001;Jambunathan and McNellis, 2003;Yang and Hua, 2004;Yang et al, 2006). BON1 is an infection-activated gene and encodes a protein from the copine family that has been shown to function as a negative regulator of plant defense responses.…”

Lesion mimic mutants

“…11,12 Copines are Ca 2+ -dependent, phospholipid-binding proteins that repress cell death. 54 They are connected to membrane trafficking and Ca 2+ signal transduction. They possess a von Willebrand A (VWA) domain for protein interaction and a C2 domain that mediates the membrane association.…”