Prospecting the Potential of Plant Growth-Promoting Microorganisms for Mitigating Drought Stress in Crop Plants.

Drought is a global phenomenon affecting plant growth and productivity, the severity of which has impacts around the whole world. A number of approaches, such as agronomic, conventional breeding, and genetic engineering, are followed to increase drought resilience; however, they are often time consuming and non-sustainable. Plant growth-promoting microorganisms are used worldwide to mitigate drought stress in crop plants. These microorganisms exhibit multifarious traits, which not only help in improving plant and soil health, but also demonstrate capabilities in ameliorating drought stress. The present review highlights various adaptive strategies shown by these microbes in improving drought resilience, such as modulation of various growth hormones and osmoprotectant levels, modification of root morphology, exopolysaccharide production, and prevention of oxidative damage. Gene expression patterns providing an adaptive edge for further amelioration of drought stress have also been studied in detail. Furthermore, the practical applications of these microorganisms in soil are highlighted, emphasizing their potential to increase crop productivity without compromising long-term soil health. This review provides a comprehensive coverage of plant growth-promoting microorganisms-mediated drought mitigation strategies, insights into gene expression patterns, and practical applications, while also guiding future research directions.

Advancement in the molecular perspective of plant-endophytic interaction to mitigate drought stress in plants.

Change in global climate has started to show its effect in the form of extremes of temperatures and water scarcity which is bound to impact adversely the global food security in near future. In the current review we discuss the impact of drought on plants and highlight the ability of endophytes, microbes that inhabit the plants asymptomatically, to confer stress tolerance to their host. For this we first describe the symbiotic association between plant and the endophytes and then focus on the molecular and physiological strategies/mechanisms adopted by these endophytes to confer stress tolerance. These include root alteration, osmotic adjustment, ROS scavenging, detoxification, production of phytohormones, and promoting plant growth under adverse conditions. The review further elaborates on how omics-based techniques have advanced our understanding of molecular basis of endophyte mediated drought tolerance of host plant. Detailed analysis of whole genome sequences of endophytes followed by comparative genomics facilitates in identification of genes involved in endophyte-host interaction while functional genomics further unveils the microbial targets that can be exploited for enhancing the stress tolerance of the host. Thus, an amalgamation of endophytes with other sustainable agricultural practices seems to be an appeasing approach to produce climate-resilient crops.

Prospecting potential of endophytes for modulation of biosynthesis of therapeutic bioactive secondary metabolites and plant growth promotion of medicinal and aromatic plants.

Medicinal and aromatic plants possess pharmacological properties (antidiabetes, anticancer, antihypertension, anticardiovascular, antileprosy, etc.) because of their potential to synthesize a wide range of therapeutic bioactive secondary metabolites. The concentration of bioactive secondry metabolites depends on plant species, local environment, soil type and internal microbiome. The internal microbiome of medicinal plants plays the crucial role in the production of bioactive secondary metabolites, namely alkaloids, steroids, terpenoids, peptides, polyketones, flavonoids, quinols and phenols. In this review, the host specific secondry metabolites produced by endophytes, their therapeutic properties and host-endophytes interaction in relation to production of bioactive secondry metaboloites and the role of endophytes in enhancing the production of bioactive secondry metabolites is discussed. How biological nitrogen fixation, phosphorus solubilization, micronutrient uptake, phytohormone production, disease suppression, etc. can play a vital role in enhacing the plant growth and development.The role of endophytes in enhancing the plant growth and content of bioactive secondary metabolites in medicinal and aromatic plants in a sustainable mode is highlighted.

Prospect of pink pigmented facultative methylotrophs in mitigating abiotic stress and climate change.

Apparently, climate change is observed in form of increased greenhouse gases (CH4 , CO2 , N2 O, CFC), temperature (0.5-1°C), and UV radiations (UV B and UV C). It is affecting every aspect of ecosystem functioning; however, terrestrial crops are the most vulnerable group and crop productivity largely remains a challenge. Due to climate change, seed yield and nutrient depletion are inevitable in future scenarios. To overcome this problem microbial groups that exhibit plant growth promoting attributes and provide protection against environmental stress should be studied. One such group is the pink pigmented facultative methylotrophs (PPFMs) that can induce overall fitness to plants. PPFMs are involved in phosphorous mineralization, siderophore, ACC deaminase, phytohormone production, and assimilation of greenhouse gases. Additionally, these organisms can also resist harmful UV radiations effectively as they possess polyketide synthases that could serve as source of novel bioactives that can protect plant from abiotic stress. The review article comprehensively highlights the multifunctional traits of PPFMs and their role in mitigating climate change with an aim to use this important organism as microbial inoculants for sustainable agriculture under climate-changing scenarios.

Methylotroph bacteria and cellular metabolite carotenoid alleviate ultraviolet radiation-driven abiotic stress in plants.

Increasing UV radiation in the atmosphere due to the depletion of ozone layer is emerging abiotic stress for agriculture. Although plants have evolved to adapt to UV radiation through different mechanisms, but the role of phyllosphere microorganisms in counteracting UV radiation is not well studied. The current experiment was undertaken to evaluate the role of phyllosphere Methylobacteria and its metabolite in the alleviation of abiotic stress rendered by ultraviolet (UV) radiation. A potential pink pigmenting methylotroph bacterium was isolated from the phylloplane of the rice plant (oryzae sativa). The 16S rRNA gene sequence of the bacterium was homologous to the Methylobacter sp. The isolate referred to as Methylobacter sp N39, produced beta-carotene at a rate (µg ml-1 d-1) of 0.45-3.09. Biosynthesis of beta-carotene was stimulated by brief exposure to UV for 10 min per 2 days. Carotenoid biosynthesis was predicted as y = 3.09 × incubation period + 22.151 (r 2 = 0.90). The carotenoid extract of N39 protected E. coli from UV radiation by declining its death rate from 14.67% min-1 to 4.30% min-1 under UV radiation. Application of N39 cells and carotenoid extract also protected rhizobium (Bradyrhizobium japonicum) cells from UV radiation. Scanning electron microscopy indicated that the carotenoid extracts protected E. coli cells from UV radiation. Foliar application of either N39 cells or carotenoid extract enhanced the plant's (Pigeon pea) resistance to UV irradiation. This study highlight that Methylobacter sp N39 and its carotenoid extract can be explored to manage UV radiation stress in agriculture.

Synergistic effects of silver nanoparticles augmented Calothrix elenkinii for enhanced biocontrol efficacy against Alternaria blight challenged tomato plants.

The biocontrol efficacy of a cyanobacterium Calothrix elenkinii (Ce), silver nanoparticles (AgNPs) and their augmented complex (AgNPs-Ce) was evaluated. Foliar application of AgNPs-Ce reduced the disease severity by 47-58%, along with significant increases of 44-45%, 40-46% and 23-33% in leaf chlorophyll, carotenoid content, and polyphenol oxidase activity in the A. alternata infected tomato plants. A significant reduction in the pathogen load was recorded, both by plate counts and microscopic observations in the AgNPs, Ce and AgNPs-Ce treatments, while AgNPs-Ce also effectively reduced ergosterol content by 63-79%. Amplification using PCR-ITS primers revealed very faint bands or none in the AgNPs-Ce treated leaves, illustrating the inhibition of fungal growth. Significantly higher yield was recorded in the pathogen challenged plants receiving AgNPs-Ce, AgNPs, and Ce treatments. Higher expression of elicited antioxidant enzymes, along with enhanced plant growth attributes and lowered fungal load highlight the biocontrol potential of AgNPs-Ce treatment in A. alternata infected plants. This synergistic association can be explored as a promising biocontrol option against A. alternata challenged tomato plants under various agroclimatic conditions.