Overviewing Drought and Heat Stress Amelioration—From Plant Responses to Microbe-Mediated Mitigation

Microbes (e.g., plant-growth-promoting rhizobacteria, arbuscular mycorrhizal fungi and endophytes) are the natural inhabitants of the soil-plant-environment ecosystem having the potential to ameliorate the negative effects of environmental extremities. Plant-microbe interactions are integral events of agricultural ecosystems which must be studied in order to modulate the systemic mechanisms in field crops. Under changing climatic scenarios, drought and heat stresses tend to induce numerous physiological, morphological, metabolic and biochemical alterations in crop plants, while microbes hold the potential to mitigate these adverse impacts in a sustainable way. However, plant-microbe interaction mechanisms remain understudied owing to their complexities in the rhizosphere and within the cellular systems of plants. In this review, we have attempted to summarize microbes’ interactions with crop plants that tend to influence hormonal and nutrients balance, and the biosynthesis of metabolites and phytohormones, etc. In particular, focus has been kept on the underlying mechanisms related to plant-microbe interactions which confer abiotic stress tolerance. Moreover, various physiological, morphological, metabolic and biochemical responses of plants subjected to water scarcity and elevated temperatures have been synthesized objectively. Lastly, from the perspective of microbes’ application as biofertilizers, both challenges and future research needs to develop microbe-mediated tolerance as a biologically potent strategy have been strategically pointed out.