A FeuP-FeuQ-Dependent Regulatory Module Integrating Envelope Stress and Host-Associated Behaviors in Agrobacterium tumefaciens

Abstract

Agrobacterium tumefaciens is an important plant pathogen, the causative agent of crown gall disease, and a foundational technology used for genetic transformation of plant tissue. More recently, A. tumefaciens has been adopted as a genetically tractable model organism for studying bacterial cell cycle regulation, developmental pathways, and niche construction. The transition from a free-living bacterium within the rhizosphere to association with a plant host and subsequent transformation of plant tissue is one aspect of A. tumefaciens life history that encompasses all three of these processes. Such events are coordinated by multiple regulatory modules which must sense external and/or internal cues, integrate these inputs, and effect appropriate changes in gene expression and cellular responses to maximize fitness. Here, we evaluate the contribution of the two-component system, FeuP-FeuQ, to gene expression and developmental phenotypes including surface attachment/biofilm formation, swimming motility, and tumorigenesis. feuPQ operon organization suggests translational coupling during expression of the response regulator, FeuP (Atu0970), and sensor kinase, FeuQ (Atu0971). In-frame, non-polar deletion of feuP or feuQ individually, or the entire feuPQ operon, resulted in reduced biofilm formation, swimming motility, and tumor formation, without adversely affecting planktonic growth. Transcriptomic profiling identified [~]300 differentially expressed genes when the feuPQ locus was disrupted, including genes affecting flagellar motility, succinoglycan production, and type VI secretion. Phenotype profiling emphasized the contribution of feuPQ to withstanding osmotic, ionic, and antimicrobial stressors. Together, these data highlight FeuPQ as a global regulator of cellular responses which likely contribute to overall fitness during rhizosphere lifestyle transitions. IMPORTANCEAgrobacterium tumefaciens is an important plant pathogen able to genetically transform numerous plant species. In the rhizosphere, this bacterium encounters many challenges ranging from antagonistic and competing microbes, to plant host defenses, to rapidly changing environmental conditions. Efficient host interaction leading to plant transformation requires coordination of bacterial motility, attachment, and defense mechanisms, among other processes. This work identifies two proteins, FeuP and FeuQ, that together contribute to such coordination. The importance of this work is in identifying the FeuPQ system as a global regulator of these and other processes, possibly enabling targeted interventions to promote or inhibit plant transformation.