The above ground growth of the plant is highly dependent on the belowground root system. Rhizosphere is the zone of continuous interplay between plant roots and soil microbial communities. Plants, through root exudates, attract rhizosphere microorganisms to colonize the root surface and internal tissues. Many of these microorganisms known as plant growth promoting rhizobacteria (PGPR) improve plant growth through several direct and indirect mechanisms including biological nitrogen fixation, nutrient solubilization, and disease-control. Many PGPR, by producing phytohormones, volatile organic compounds, and secondary metabolites play important role in influencing the root architecture and growth, resulting in increased surface area for nutrient exchange and other rhizosphere effects. PGPR also improve resource use efficiency of the root system by improving the root system functioning at physiological levels. PGPR mediated root trait alterations can contribute to agroecosystem through improving crop stand, resource use efficiency, stress tolerance, soil structure etc. Thus, PGPR capable of modulating root traits can play important role in agricultural sustainability and root traits can be used as a primary criterion for the selection of potential PGPR strains. Available PGPR studies emphasize root morphological and physiological traits to assess the effect of PGPR. However, these traits can be influenced by various external factors and may give varying results. Therefore, it is important to understand the pathways and genes involved in plant root traits and the microbial signals/metabolites that can intercept and/or intersect these pathways for modulating root traits. The use of advanced tools and technologies can help to decipher the mechanisms involved in PGPR mediated determinants affecting the root traits. Further identification of PGPR based determinants/signaling molecules capable of regulating root trait genes and pathways can open up new avenues in PGPR research. The present review updates recent knowledge on the PGPR influence on root architecture and root functional traits and its benefits to the agro-ecosystem. Efforts have been made to understand the bacterial signals/determinants that can play regulatory role in the expression of root traits and their prospects in sustainable agriculture. The review will be helpful in providing future directions to the researchers working on PGPR and root system functioning.

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Plants respond to abiotic stresses through a series of molecular, cellular and physiological changes. These responses are further influenced by the interactions between host plant and the associated rhizospheric and endophytic microorganisms. The endophytic microorganisms, due to their intimate proximity with the host plant, are considered to have major influence on plant’s physiological responses. In the present study, three drought tolerant and plant growth promoting maize seed endophytic bacteria, Bacillus sp. MSEB 17, Bacillus sp. MSEB 72 and Bacillus sp. MSEB 78 were used as seed inoculants in maize (var Bioseed 9681) under drought stress conditions in a growth chamber pot study and their influence on four drought responsive genes (Zmdhn1, GRMZM2G055844, GRMZM2G467339 and GRMZM2G109448) in maize leaves was studied by real time PCR using specific primers. The influence of inoculation on host plant’s response to drought was evident from altered expression of target genes when compared with uninoculated plants. Notably, inoculation with MSEB 17 increased the expression of three target genes, Zmdhn1 (dehydrin) gene, GRMZM2G467339 gene and GRMZM2G109448 gene by several folds.  This study revealed the role of endophytic in alleviating the effect of drought stress in maize plants through regulating plant growth and physiological response.