Abstract
Plant Resistance (R) genes encode immune receptors that recognize pathogens and activate defense responses. Because of fitness costs associated with maintaining R protein-mediated resistance, expression levels of R genes have to be tightly regulated. However, mechanisms on how R-gene expression is regulated are poorly understood. Here we show that MODIFIER OF snc1, 1 (MOS1) regulates the expression of SUPPRESSOR OF npr1-1, CONSTITUTIVE1 (SNC1), which encodes a Toll/interleukin receptor-nucleotide binding site-leucine-rich repeat type of R protein in Arabidopsis (Arabidopsis thaliana). In the mos1 loss-of-function mutant plants, snc1 expression is repressed and constitutive resistance responses mediated by snc1 are lost. The repression of snc1 expression in mos1 is released by knocking out DECREASE IN DNA METHYLATION1. In mos1 mutants, DNA methylation in a region upstream of SNC1 is altered. Furthermore, expression of snc1 transgenes using the native promoter does not require MOS1, indicating that regulation of SNC1 expression by MOS1 is at the chromatin level. Map-based cloning of MOS1 revealed that it encodes a novel protein with a HLA-B ASSOCIATED TRANSCRIPT2 (BAT2) domain that is conserved in plants and animals. Our study on MOS1 suggests that BAT2 domain-containing proteins may function in regulation of gene expression at chromatin level.
Highlights
Plant Resistance (R) genes encode immune receptors that recognize pathogens and activate defense responses
Whereas the phenotypes in snc1 are caused by the deregulated activation of the R protein, the phenotypes of bal are caused by increased expression of SNC1 in the mutant. bal was recovered from plants carrying the decrease in DNA methylation1 loss-of-function mutation, which results in a reduction in cytosine methylation throughout the genome (Vongs et al, 1993)
Arabidopsis npr1 is required for salicylic acid (SA)-induced PR gene expression (Dong, 2004)
Summary
Plant Resistance (R) genes encode immune receptors that recognize pathogens and activate defense responses. We show that MODIFIER OF snc (MOS1) regulates the expression of SUPPRESSOR OF npr, CONSTITUTIVE1 (SNC1), which encodes a Toll/interleukin receptor-nucleotide binding site-leucine-rich repeat type of R protein in Arabidopsis (Arabidopsis thaliana). In the mos loss-offunction mutant plants, snc expression is repressed and constitutive resistance responses mediated by snc are lost. Our study on MOS1 suggests that BAT2 domain-containing proteins may function in regulation of gene expression at chromatin level. The gain-of-function mutation snc leads to constitutive activation of the R protein and downstream defense responses without the presence of pathogens. Snc mutant plants accumulate high levels of SA, constitutively express PR genes, and display enhanced resistance to pathogens (Li et al, 2001). EDM2 belongs to a plant-specific protein family with typical features of transcriptional regulators
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