Editorial: The Role of Plant Hormones in Plant-Microbe Symbioses

Plant hormones are regulators of almost all aspects of plant development and plant responses to their environment. Active at very low concentrations, with tight spatial regulation of synthesis and response, many plant hormones have key roles in the interactions between plants and beneficial microbes. In this special issue, “The Role of Plant Hormones in Plant-Microbe Symbioses,” new insights are revealed into how hormones derived from both the plant and microbial partner play roles in communication, symbioses establishment, and function. This includes intimate endosymbioses with arbuscular mycorrhizal (AM) fungi formed by the majority of land plants and the more recently evolved nodulation, the symbioses between a limited set of plants in the fabid clade and nitrogen-fixing bacteria. Articles in this special issue also explore the role of hormones in plant interactions with ectomycorrhizae, endophytic bacteria and fungi, as well as beneficial microbes that associate with the root or leaf surfaces. In addition to acting directly, many hormones can interact with each other to control the development of these symbioses, and these complex networks are now emerging.