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. 2011 Feb 8;12(7):628–637. doi: 10.1111/j.1364-3703.2010.00698.x

Figure 3.

Figure 3

Model depicting the regulatory cascade of the Hrp system in Pnss. HrpX and HrpY constitute a two‐component regulatory system where HrpX is the sensor and HrpY is the corresponding response regulator. hrpXY expression is both constitutive and induced. HrpX transfers phosphate to HrpY and phosphorylated HrpY activates transcription of hrpS. HrpS is an enhancer binding protein that is needed for expression of hrpL. HrpL is an alternate sigma factor that activates transcription of both the entire hrp gene cluster and the wts gene cluster. The hrpS promoter appears to be a point in the cascade where several specific and global regulators (RsmA and Lon protease) converge to control hrp gene expression. In addition, there is a novel transcriptional autoregulatory mechanism of the hrpL/hrpX/hrpX/hrpS gene cluster that is triggered by HrpS (dark grey arrow) and may allow Pnss to rapidly turn on central hrp genes when it initially enters the plant. Figure adapted from Merighi et al. (2005). Note: Figure not drawn to scale.