Bacterial Biosynthesis of Indole-3-Acetic Acid: Signal Bacterial Biosynthesis of Indole-3-Acetic Acid: Signal Messenger Service

Plant health and soil quality are continuously challenged by increasing environmental stresses and phytopathogen attack. They are often, however, provided a helping hand by unseen microbial inhabitants in the rhizosphere. In this context bacterial biosynthesis of the auxin phytohormone, indole-3-acetic acid (IAA) is well established, as it can positively regulate developmental processes of plant roots. Auxins, and especially IAA, have been shown to have specific but amazingly contrasting roles such as in the virulence of phytopathogens and their disease-causing ability, as well as in the well-known process of symbiosis, and the salicylic-acid-dependent plant defense response. Bacterial IAA can be synthesized through a number of pathways and may be subjected to multipronged regulation by a variety of mechanisms and regulators. IAA can act as a signaling molecule in microorganisms and plant-microbe interactions as IAA affects gene expression in both plants and microorganisms. There is also growing evidence for the interaction of IAA with other plant growth regulators, nitric oxide and ethylene. This interactive network of biomolecules can greatly impact the host.