AUTHOR=Liu Tengfei , Cao Li , Cheng Yuanyuan , Ji Jing , Wei Yongshu , Wang Chenchen , Duan Kaixuan 

TITLE=MKK4/5-MPK3/6 Cascade Regulates Agrobacterium-Mediated Transformation by Modulating Plant Immunity in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.731690

DOI=10.3389/fpls.2021.731690

ISSN=1664-462X

ABSTRACT=<p><italic>Agrobacterium tumefaciens</italic> is a specialized plant pathogen that causes crown gall disease and is commonly used for <italic>Agrobacterium</italic>-mediated transformation. As a pathogen, <italic>Agrobacterium</italic> triggers plant immunity, which affects transformation. However, the signaling components and pathways in plant immunity to <italic>Agrobacterium</italic> remain elusive. We demonstrate that two <italic>Arabidopsis</italic> mitogen-activated protein kinase kinases (MAPKKs) MKK4/MKK5 and their downstream mitogen-activated protein kinases (MAPKs) MPK3/MPK6 play major roles in both <italic>Agrobacterium</italic>-triggered immunity and <italic>Agrobacterium</italic>-mediated transformation. Agrobacteria induce MPK3/MPK6 activity and the expression of plant defense response genes at a very early stage. This process is dependent on the MKK4/MKK5 function. The loss of the function of <italic>MKK4</italic> and <italic>MKK5</italic> or their downstream <italic>MPK3</italic> and <italic>MPK6</italic> abolishes plant immunity to agrobacteria and increases transformation frequency, whereas the activation of MKK4 and MKK5 enhances plant immunity and represses transformation. Global transcriptome analysis indicates that agrobacteria induce various plant defense pathways, including reactive oxygen species (ROS) production, ethylene (ET), and salicylic acid- (SA-) mediated defense responses, and that MKK4/MKK5 is essential for the induction of these pathways. The activation of MKK4 and MKK5 promotes ROS production and cell death during agrobacteria infection. Based on these results, we propose that the MKK4/5-MPK3/6 cascade is an essential signaling pathway regulating <italic>Agrobacterium</italic>-mediated transformation through the modulation of <italic>Agrobacterium-</italic>triggered plant immunity.</p>