Pathogenic bacteria target plant plasmodesmata to colonize and invade surrounding tissues

A hallmark of multicellular organisms is their ability to maintain physiological homeostasis by communicating among cells, tissues, and organs. In plants, intercellular communication is largely dependent on plasmodesmata (PD), which are membrane-lined channels connecting adjacent plant cells. Upon immune stimulation, plants close PD as part of their immune responses. Here, we show that the bacterial pathogen Pseudomonas syringae deploys an effector protein HopO1-1 to modulate the function of PD. HopO1-1 is required for P. syringae to spread locally to neighboring tissues during infection. Expression of HopO1-1 in Arabidopsis increases the distance of PD-dependent molecular flux between neighboring plant cells. Being a putative ribosyltransferease, the catalytic activity of HopO1-1 is required for regulation of PD. HopO1-1 physically interacts with and destabilizes plant PD-located proteins PDLP7 and possibly PDLP5. Both PDLPs are involved in bacterial immunity. Our findings reveal that a pathogenic bacterium utilizes an effector to manipulate PD-mediated host intercellular communication for maximizing the spread of bacterial infection.