Two-Component Sensory Transduction Systems in Phytobacteria

Abstract

Prokaryotic plant pathogens and symbionts have dynamic lifestyles in which they fill multiple niches in their life cycles. These organisms must be able to compete successfully against other organisms, often in the soil and rhizo­ sphere, and also take advantage of very specialized plant habitats. To achieve this, they must have mechanisms for altering their gene expression rapidly and efficiently in response to environmental signals. Initiation of the in­ teractions that lead to varied relationships with the plant requires that several genes be coordinately regulated. In many cases, following infection, another set of genes is expressed during prolonged interaction between bacteria and their plant host. Not surprisingly, many of the genes are regulated in direct response to recognition of specific plant-derived compounds or host-asso­ ciated conditions. Prokaryotic two-component sensory transduction systems (83, 104, 135) are often parts of complex regulatory networks and cascades. They are of prime importance in transmitting environmental signals and regulating adap­ tive responses. In general, these systems are made up of a sensor protein and a response regulator protein. The sensors share C terminus homology, while the response regulators share N terminus homology. The sensor proteins are histidine protein kinases that autophosphorylate in direct or indirect response