Plant hormones produced by microbes

Abstract

Plant hormones or phytohormones are historically classified into five major classes: auxins, cytokinins, gibberellins, abscisic acid and ethylene. Nowadays, many other phytohormones have been identified. Diverse microbial species possess the ability to produce phytohormones, with most data accumulated for the production and role of auxin. In this chapter the microbial biosynthesis, its regulation and the role of the different phytohormones in the interaction with the plant are discussed. Microbial phytohormonal production is a potent mechanism to alter plant physiology, leading to diverse outcomes from pathogenesis to promotion of plant growth. However, genetic evidence for the role of many phytohormones in microbe-plant interactions is still lacking, thus questioning the importance of the microbial production. Targeted approaches focusing on genetic evidence for the role of phytohormones together with plant experiments in an agronomic setting will allow unraveling the importance and potential of this fascinating microbial trait.