Root Colonization and Molecular Mechanism of Plant Growth Promotion by the Plant-Associated Probiotic Bacteria

Plant-associated probiotic bacteria inhabit and confer numerous beneficial traits to their host plant through plant-bacteria interactions. These bacteria colonize the interior spaces of their hosts and make up a major portion of the plant microbiome. Interactions between plants and their corresponding associated (endophyte and epiphytes) bacteria cater to an array of advantages including plant tolerance enhancements to environmental changes, plant growth promotions, and protection which make them an ideal choice for progressive agricultural practices. A diverse collection of bacteria serves as endophytes in different plant species, and within these bacterial strains, studies revealed specifically expressed genes to be responsible, which endowed such beneficial characteristics to their hosts. This chapter reviews and discusses the microbial diversity as well as classification of plant-associated bacteria, their mode of root colonization, and the direct and indirect methods along with traits that facilitate competitive colonization of these endophytic and epiphytic plant bacteria that help in plant growth promotion.