In Sal monella , the PhoP-PhoQ two-component signal transduction system (TCS) is a maj or regulator of virulence , consisting of the trans-membrane sensor , PhoQ, and the cytoplasmic regulator , PhoP. PhoP-PhoQ can regulate Salmonella adaption to a low Mg²⁺ environment and other periplasmic signals , mediating transcription and expression of genes that encode proteins essential to bacterial virulence in the host cell . PhoP-PhoQ is necessary f or Salmonella in epithelium cell invasion, survival within macrophages , resistance to anti microbial peptides , modification of li pid A, function of type Ⅲ secretion system, and pathogenesis . PhoP- PhoQ can also interact with other TCSs or regulators to forma perfect regulative networkto ensure the regulation more suitable and well- rounded. Theref ore , PhoP-PhoQplays an important role in the regulation of Salmonella virulence .