Auxins-Interkingdom Signaling Molecules

Abstract

Phytohormones play a fundamental role in the development of plants. Among various phytohormones produced by the plants, Auxins act as a master hormone that plays a major role during plant development and differentiation through cell division. Besides plants, many rhizospheric microorganisms are also capable of producing auxins specifically indole-3-acetic acid (IAA), that act as signaling molecules for the regulation of gene expressions in plants. However, bacterial IAA is majorly linked with the modulation of plant roots architecture and developing positive plant-microbe interactions. Bacterial auxin modifies root morphology by enhancing root length, forming adventitious root and root hair, thereby, increasing surface area for water and nutrient absorption affecting various aspects of plant biology in a number of ways. Bacteria mostly utilize tryptophan, present in plant root exudates, to synthesize IAA that eventually helps bacteria to colonize roots by establishing beneficial associations with plant roots. Auxins also stimulate the formation of exopolysaccharides and biofilms that help bacterial root colonization. Auxins have given the survival benefit to rhizobacteria that make them more competent to establish symbiotic interaction with plants. Synergistic and antagonistic interactions of auxins (both interkingdom and Intrakingdom) with other phytohormones play a key role in plant development and growth improvement.

Bacterial Symbiotic Signaling in Modulating Plant-Rhizobacterial Interactions

“…Tryptophan is most significant amino acid exuded by plants. Microbes in root vicinity detoxify tryptophan and produce auxins [56]. PIN proteins mediated auxin flux allows initiation of cell-to-cell communicating network [57].…”

“…Hence, rhizobacterial colonization is regulated by the interaction of IAA and QS signals and their high survival is also linked with biofilm production. IAA plays important role in modulating gene expression of bacterial cells and making them more competent [56]. Transcriptome analysis revealed that IAA signaling causes downregulation and upregulation of various respiration affecting genes in rhizobacteria [62].…”

Phosphate solubilization potential of PSB: An advance approach to enhance phosphorous availability for phytostimulation

“…It is one of the most common plants limiting nutrient, therefore, its acquisition is always considered a supreme problem throughout the world in agricultural sector. Rhizospheric soil phosphate solubilizing bacteria are the active agents that stimulate the presence of available phosphate in root vicinity and ensure its continuous supply to plants (Tariq and Ahmed, 2022 a). Due to their various advantages such as low cost, environment friendly nature, high biological efficiency and strong phytostimulatory potential, these microbes are the focus of interest for various agricultural researchers around the world.…”

“…Various species of Bacillus, Pseudomonas, Achromobacter, have been reported to produce IAA(Wagi and Ahmed, 2019;Santana et al 2022;Jain et al 2023). Production of bacterial IAA interacts with various plant metabolic pathways and maintain plant hormonal homeostasis with control overall plant development(Tariq and Ahmed, 2022 b). All the PSB have shown increment in plant morphophysiological traits depending upon bacterial nature and association with plants.…”