Implication of Microbial Signals: Plant Communication

A large number of organisms inhabit the rhizosphere. Mainly through chemical communication, interactions among roots and rhizosphere community members are accomplished. Root exudates contain a range of primary and secondary plant metabolites, which can entice, dissuade, or annihilate “herbivores,” “nematodes,” and “microbes” from insects below the ground and impede competing plants. Plants generate a broad range of organic agents, including “sugars,” “organic acids,” and “vitamins,” which can be used by microbial populations as nutrients or signals. Microorganisms release phytohormones, molecules, or volatile compounds directly or indirectly, which can trigger the immunity of plantations or restrict the growth and morphology of plants. And on the other hand, root exudate metabolomics can conceivably aid in understanding this chemical dialogue. Several inventive mechanisms were characterized to interact with their host pathogenic and beneficial microbes in the plant microbiome, including the provision of immunosuppressive effector proteins and the generation of “phytohormones,” “toxins,” and other “bioactive compounds.” Plants signal their associated microbes through exudation of photosynthesizing fixed “carbon sources,” “mimicry molecules sensing quorum,” and selective “secondary metabolites” such as “flavonoids” and “toxins.” The development of both beneficial and pathogenic plant–microbe relationship thus includes molecular communication. In this chapter, the current knowledge on small molecules, which can serve as a reporter for the growth and health of plants by beneficial microbes and as plant invasion weapons by pathogenic substances, is described.