Proven and potential involvement of vitamins in interactions of plants with plant growth-promoting bacteria—an overview

Plant growth-promoting bacteria (PGPB) can improve plant performance in many different ways, operating via a multitude of physiological, molecular, and biochemical pathways. One of the lesser known involvements in these interactions is the role of vitamins. Vitamins can be produced by plants and bacteria and also by PGPB. The main function of vitamins is to (1) act as a cofactor in diverse metabolic pathways, (2) facilitate production of essential compounds for plants and bacteria, (3) induce resistance against pathogens, (4) directly promote plant growth, and (5) participate in energy conversion in the plant from stored compounds. Most of the roles of specific vitamins in PGPB–plant interactions are still little known or completely unknown. This overview presents what is known about vitamins detected in potential PGPB, presents proposals for the potential role of vitamins in PGPB–plant interactions based on the known function of these vitamins in plants and bacteria, and proposes research avenues in this topic that are worth exploring.