An MKP-MAPK protein phosphorylation cascade controls vascular immunity in plants

Abstract

Global crop production is greatly reduced by vascular diseases. These diseases include bacterial blight of rice and crucifer black rot caused by <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) and <i>Xanthomonas campestris</i> pv. <i>campestris</i> (<i>Xcc</i>). The molecular mechanisms that activate vascular defense against such pathogens remains underexplored. Here, we show that an <i>Arabidopsis</i> MAPK phosphatase 1 (MKP1) mutant has increased host susceptibility to the adapted pathogen <i>Xcc</i> and is compromised in nonhost resistance to the rice pathogen <i>Xoo</i>. MKP1 regulates MAPK-mediated phosphorylation of the transcription factor MYB4 that negatively regulates vascular lignification through inhibiting lignin biosynthesis. Induction of lignin biosynthesis is, therefore, an important part of vascular-specific immunity. The role of MKP-MAPK-MYB signaling in lignin biosynthesis and vascular resistance to <i>Xoo</i> is conserved in rice, indicating that these factors form a tissue-specific defense regulatory network. Our study likely reveals a major vascular immune mechanism that underlies tissue-specific disease resistance against bacterial pathogens in plants.