Plant growth-promoting rhizobacteria: Salt stress alleviators to improve crop productivity for sustainable agriculture development

Abstract

Soil salinity, a growing issue worldwide, is a detrimental consequence of the ever-changing climate, which has highlighted and worsened the conditions associated with damaged soil quality, reduced agricultural production, and decreasing land areas, thus resulting in an unsteady national economy. In this review, halo-tolerant plant growth-promoting rhizo-microbiomes (PGPRs) are evaluated in the salinity-affected agriculture as they serve as excellent agents in controlling various biotic–abiotic stresses and help in the augmentation of crop productivity. Integrated efforts of these effective microbes lighten the load of agro-chemicals on the environment while managing nutrient availability. PGPR-assisted modern agriculture practices have emerged as a green strategy to benefit sustainable farming without compromising the crop yield under salinity as well as salinity-affected supplementary stresses including increased temperature, drought, salinity, and potential invasive plant pathogenicity. PGPRs as bio-inoculants impart induced systemic tolerance (IST) to plants by the production of volatile organic compounds (VOCs), antioxidants, osmolytes, extracellular polymeric substances (EPS), phytohormones, and ACC-deaminase and recuperation of nutritional status and ionic homeostasis. Regulation of PGPR-induced signaling pathways such as MAPK and CDPK assists in salinity stress alleviation. The “Next Gen Agriculture” consists of the application of designer crop microbiomes through gene editing tools, for instance, CRISPR, and engineering of the metabolic pathways of the microbes so as to gain maximum plant resistance. The utilization of omics technologies over the traditional approaches can fulfill the criteria required to increase crop yields in a sustainable manner for feeding the burgeoning population and augment plant adaptability under climate change conditions, ultimately leading to improved vitality. Furthermore, constraints such as the crop specificity issue of PGPR, lack of acceptance by farmers, and legal regulatory aspects have been acknowledged while also discussing the future trends for product commercialization with the view of the changing climate.

The Contribution of PGPR in Salt Stress Tolerance in Crops: Unravelling the Molecular Mechanisms of Cross-Talk between Plant and Bacteria

“…In order to maintain osmotic balance both inside and outside the cell, plants increase the synthesis of low-molecularweight compatible solutes in the cytosol, also referred to as osmolytes. The most common osmolytes include proline, glycine betaine, soluble sugars, and ectoine [94,95]. Osmolytes are not charged, polar, and soluble, and do not interfere with cell metabolism even at high concentrations [49].…”

B. subtilisCNBG‐PGPR‐1 induces methionine to regulate ethylene pathway and ROS scavenging for improving salt tolerance of tomato

“…By unraveling the intricate regulatory mechanisms underlying plant‐microbe interactions, we can gain valuable insights into how PGPR exerts its beneficial effects on plant growth and stress tolerance. These findings hold great potential for advancing the development of biofertilizers and sustainable agricultural practices (Kumawat et al., 2023).…”

“…The molecular mechanisms underlying the induction of plant salt tolerance by PGPR are diverse and complex. Several reports have investigated the mechanisms through which PGPR interacts with plants, including nutrient absorption promotion, auxin production, ACC deaminase activity, and exocytosis secretion (Kang et al., 2019; Kumawat et al., 2023; Liu et al., 2021; Muthuraja & Muthukumar, 2022). Nonetheless, there are still some unknown mechanisms involved in PGPR‐induced salt tolerance in plants, and CNBG‐PGPR‐1 may represent one of these mechanisms.…”

The role of endophytes and rhizobacteria to combat drought stress in wheat

“…Understanding the specific roles of different rhizobacteria in modulating hormone signaling pathways in plants has the potential to drive innovative approaches for enhancing plant growth and improving overall plant health in agricultural and environmental contexts (A. . According to many studies, the proportion of plant PGPR-assisted hormones during stress conditions performs better than a single hormone in plants (Guan et al, 2023;Kumawat et al, 2023). Liu and Wei (2019) found drought exposure affected seedlings GA:ABA and zeatin riboside (ZR):IAA ratios.…”