Chapter Six – Chatting With a Tiny Belowground Member of the Holobiome: Communication Between Plants and Growth-Promoting Rhizobacteria.

As sessile organisms, plants have facilitated to actively protect themselves against biotic and abiotic stresses. For this, plants keep communicating with other organisms including insect and microbes inside and outside plant surface including root surface. In the area around the root referred to as the rhizosphere, diverse root-associated bacteria interact with plants with both positive and negative effects. In the past three decades, a group of rhizosphere bacteria known as plant growth-promoting rhizobacteria (PGPR) have been intensively studied for possible use in improving plant health. Here, we provide an overview of the current knowledge on the nature of PGPR, their signatures and their roles in plant growth promotion and biological control against plant pathogens, as revealed by classic physiological and morphological observations and recent cutting-edge technology. We also discuss new information on insect–plant–PGPR tritrophic interactions, as well as technology transfer from the laboratory to the field. We use the new concept of the holobiome to help elucidate plant–PGPR interactions. Understanding plant root–bacterial communications in this novel framework may facilitate the improvement of plant health in agricultural production systems. [ABSTRACT FROM AUTHOR]