IAA Biosynthesis in Bacteria and Its Role in Plant-Microbe Interaction for Drought Stress Management

Abstract

Globally, the availability of water for irrigation is decreasing for agricultural practices, including different growing crops. The productivity of different crops is declining as the time duration of drought conditions is increasing. The plants have been adapting different strategies including morphological changes, modulation on physiological process and maintaining the osmotic potential of cell to counter the drought stress condition. Diverse microbes associated with plants reported as plant growth-promoting rhizobacteria (PGPR), having PGP activity including P-solubilization, indole acetic acid (IAA) synthesis, siderophore production and antifungal activity. While, some PGPR having additional characteristics i.e. nitrogen fixing activity and PGPR without N-fixing ability, can postulated the improvement of different parameter for crop (root biomass, shootbiomass, crop yield, root architecture) leading to enhancement in capability to drought stress conditions by different mechanisms. Additionally, the modification of root and shoot of plants by physio-biochemical activity of inole-3-acetic acid (IAA) secreted by diverse microbes in rhizosphere during plant–microbe interaction is a key process to help for mitigation of drought stress in deferent crops. The IAA-secreting bacteria have operated five different pathways for biosynthesis of IAA by utilizing tryptophan as only known precursor. While some IAA-producing bacteria also synthesize IAA without tryptophan by operating tryptophan-independent pathway. The plant–microbe interaction is one of the main physiological and biochemical processes in rhizosphere where IAA has key role and involves in crosstalk between plants and microbes. Moreover, root colonization process is also a part of plant–microbe interaction in which the rhizobacteria aggressively colonize the root by biochemical signalling between rhizobacteria and plants. The root colonizing bacteria secrete various enzymes and wide range of metabolites that can help plants in improving the tolerance capacity under drought conditions. In conclusion, IAA biosynthesis from various bacteria helps in root colonization during plant–microbe interaction procedure, which leads to mitigate the drought stress in different plants by modulation in physiological and biochemical characteristics of plants.KeywordsPlant–microbe interactionDrought toleranceTryptophan-independent pathwayIAA biosynthesis pathwayDrought tolerance mechanism