Bacteria and fungi live in complex coassociations with plants and have important roles in shaping the quality of the soil and in promoting the productivity and health of the plant itself. As with the human microbiome (2), the plant microbiome has both direct and indirect relationships with its host, from transforming the availability of organic matter and essential nutrients in the soil, including nitrogen fixation, mitigating the impact of environmental stresses (such as drought or the presence of phytotoxic contaminants), to preventing the growth or activity of plant pathogens through competition for space and nutrients, antibiosis, production of hydrolytic enzymes, inhibition of pathogen-produced enzymes or toxins, and through systemic induction of plant defense mechanisms (3, 4). The most widely studied group of plant-associated microorganisms live in the soil surrounding the roots or inside the roots themselves (endophytes); the interface between roots and soil is often considered the key point of interaction between a plant and its environment. However, microbes colonizing at the root can also migrate through the plant to colonize aerial tissues, either internally or externally (epiphytes). However, the exact way in which microbes make this journey is poorly understood (3). Many microorganisms that actively colonize these tissues have multiple metabolic activities that support plant health, either by promoting growth or suppressing disease-causing pathogens; however, disassociating these two traits and assigning activities to specific taxa is often problematic because of the numerous codependent interactions between the many different species. These beneficial organisms have a very broad phylogeny, but several of them have been well studied, including bacterial genera, such as Azospirillum, Bacillus, etc. (5). In Fig. 1 we highlight some microorganisms that have shown association with the different tissues.