Revisiting plant-microbe interaction mechanisms for developing efficient biostimulants.

The diverse and often complex challenges arising from climate change, severe soil degradation and agricultural intensification due to increased use of synthetic agrochemicals, have exacerbated the need for sustainable agricultural systems that can sustain crop productivity with less reliance on agrochemicals. Plant microbe interactions really help in this transition as they influence plant growth, nutrient access, adaptation to stress, and defense against pathogens. Plants interact with many belowground microbes in the rhizosphere through an incredibly diverse set of root exudates that act as chemical cues for microbial community assembly, root colonization, nutrient cycling, and mutualistic relationships. So, the rhizosphere offers a heavily populated environment for co-evolutionary interactions among plants, microbes, and their environment that ultimately benefits plant health, soil productivity, and ecosystem sustainability. Although there have been tremendous advances in understanding the microbial component of plant microbe interactions, our mechanistic knowledge of how plants communicate with microbes, establish microbes in the root and adapt to diverse field environments has lagged behind. This discrepancy in current understanding has contributed to the ineffective use of microbial biofertilizers in agricultural systems and raises the need to revisit the fundamental mechanisms of plant microbe mutualisms to develop new biostimulants. In this review, we critically synthesize current understanding of rhizosphere communication and root exudate-mediated signalling mechanisms that promote beneficial plant microbe interactions, while examining the biological and technological challenges that affect their application in the field. We considered emerging strategies like microbial consortia, multi-omics techniques, synthetic biology and formulation technologies that aim to develop robust scalable field-validated microbial biostimulants for sustainable and climate-smart agriculture.