Plant intracellular immune receptors, or Nucleotide-binding and Leucin Rich Repeat (NLR) proteins, sense pathogen invasion and trigger robust downstream immune responses. NLR genes are tightly controlled at the transcript and protein levels to optimize plant growth and immunity. The transcription of SUPPRESSOR OF npr1, CONSTITUTIVE 1 (SNC1), one of the most well-studied NLR genes in Arabidopsis, is positively regulated by ATP-dependent chromatin remodeling, histone modifications and transcription factors. To better understand how SNC1 transcription is repressed, I isolated several SNC1 repressor mutants named smo (suppressor of mos1 bon1) from a sensitized genetic screen. All the smo single mutants are dwarf and have constitutively activated immune responses including elevated expression of more than one quarter of total NLR genes in Arabidopsis, indicating that they are all repressors of NLR gene expression. My thesis focuses on the characterization of three genes: SMO1, SMO3 and SMO2. The SMO1/HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 15 (HOS15) interacts with HISTONE DEACETYLASE 9 (HDA9), and they are directly associated with the SNC1 locus and deacetylate H3K9 at the gene. This is the first study showing that a histone modification enzyme directly binds to the SNC1 gene locus and histone deacetylation plays a key role in repressing SNC1 gene expression. The SMO3/LOW EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 2 (LOS2) encodes a glycolytic enzyme and the los2 mutant has altered primary metabolism. The defect in enolase activity of LOS2 is the cause of enhanced immunity in the los2 mutant, and the growth and immunity defects of los2 mutant are partially due to the upregulation of the SNC1 gene. This study highlights the significance of primary metabolite homeostasis on NLR gene expression. SMO2 is identified as the STRUCTURAL MAINTENANCE OF CHROMOSOMES 5 (SMC5). Current data suggests that compromised DNA damage repair is the primary cause of immunity activation in the smc5 mutant. These studies on SMO genes provide new insights on how the SNC1 gene is repressed at the transcriptional level, which helps develop a comprehensive understanding of how transcription of NLR genes is maintained at a proper level to optimize plant growth and immunity.