Induced systemic resistance -like responses elicited by rhizobia

Rhizobia are soil bacteria that engage into a mutualistic symbiosis with plants and benefit the host by fixing atmospheric N. In addition, rhizobia can be considered as biocontrol agents, contributing to plant health through direct inhibition of a wide range of pathogens. More recently, it became evident that rhizobial invasion of plant roots can also trigger an increased systemic resistance state in the host, a process resembling the Induced Systemic Resistance (ISR) mechanism. However, this indirect biocontrol property of rhizobia was relatively less explored. In this review article, we present an overview of the current knowledge of ISR -like responses induced by rhizobia, considering general characteristics of this phenomenon, discussing the molecular pathways leading to this response and highlighting potential links between ISR -like responses and the nodulation signaling pathway. A more detailed knowledge of these responses can result in development of biotechnological tools for sustainable crop production, through optimization of the systemic protective effect conferred by rhizobia.