Inter-Organismal Signaling in the Rhizosphere

Abstract

Each plant coexists with its associated microbes as a holobiont. Microbes inhabit all parts of the plant, including roots, stems, and leaves. The ability of microbes to colonize a particular plant species is fueled by release of signals by either or both partners that are only recognized by the right partner. It is now becoming increasingly clear that at least some microbe-to-plant signals can promote plant growth. This chapter focuses on the current trends in the use of plant–microbe signal compounds for sustainable agriculture, and also gives a brief description of potential areas for future research. The chapter begins with an introduction to the holobiont, with major focus on the beneficial plant–microbe interactions. The chapter then goes on to describe the various signals involved in the well studied legume–rhizobia and plant–mycorrhizal symbioses. Signals involved in other beneficial plant–microbe interactions; microbe–microbe signal interactions are also described, however, these areas are only beginning to be understood. Further into the chapter, the role of plant–microbe signals in plant growth and development under stressed and non-stressed conditions is described, listing various examples of microbes that promote growth of various crop species. The authors also mention limitations to microbial inoculant efficacy especially under field conditions, as well as the pros and cons of using single microbes, microbial consortia, and plant–microbial signals. The conclusion summarizes the chapter and gives suggestions on what future research on signal compounds needs to focus on, for optimal utilization in agricultural production.