Root exudate-driven rhizospheric recruitment of plant growth-promoting rhizobacteria

To promote growth, terrestrial plants release photosynthetic products into the rhizosphere in the form of root exudates through their root systems. Under the attraction of root exudates, plant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere to stimulate plant growth and/or suppress the growth of pathogenic microorganisms. The rhizospheric recruitment of PGPR, as well as the establishment of root–microbe interactions, are initiated by chemotaxis towards root exudates. Over the past several decades, scientists have made notable strides in identifying representative chemoeffectors in root exudates, as well as the corresponding chemoreceptors. We review here the most recent developments in rhizospheric chemotaxis, particularly the chemoeffectors in root exudates, the structural and functional characterization of methyl-accepting chemotaxis proteins of PGPR, and the impact that rhizospheric chemotaxis has on root colonization, biofilm formation, and other root–microbe interactions during recruitment. Finally, we propose several perspectives that aim to fully unlock the potential of PGPR as bioinoculants in sustainable agriculture.