The HrpX Protein Activates Synthesis of the RaxX Sulfopeptide, Required for Activation of XA21-Mediated Immunity to pv. .

Upon encountering a susceptible plant host, a bacterial pathogen expresses specific virulence factors. For example, in planta, the HrpX protein activates transcription of roughly 150 genes encoding components of the type III secretion system or its translocated effectors, as well as other secreted proteins implicated in pathogenesis. Here, we show that pv. growth in planta or in HrpX-inducing XOM2 media resulted in HrpX-dependent transcription of the and genes that control production of the RaxX sulfopeptide, exported through a type I secretion system. The RaxX protein is required for activation of XA21-mediated immunity in rice lines. We identified potential plant-inducible promoter elements upstream of the likely 5' ends of the and transcripts. Deletions and nucleotide substitutions confirmed that these elements are required for HrpX-dependent expression of and . We conclude that gene expression is induced by HrpX during growth in planta and, therefore, is coordinately expressed with other genes required for pathogenesis.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.