Biotechnological Perspectives of Legume–Rhizobium Symbiosis

Salt tolerant PGPR strain Priestia endophytica SK1 promotes Fenugreek growth under salt stress by inducing nitrogen assimilation and secondary metabolites

AIMS

Soil salinity is a huge obstacle in crop production worldwide. Saline soil can reduce active chemical contents in medicinal plants of Leguminosae family through crippled normal nodule function. Intensive efforts are underway to improve yield and medicinal value of leguminous herbs under salt stress condition by using benign microbes. Here, an attempt was made to explore the salt tolerant bacteria associated with rhizosphere of fenugreek plant (Trigonella foenum-graecum L.) and to evaluate their impact on host plant growth and metabolite of pharmaceutical importance.

METHODS AND RESULTS

A salt tolerant plant growth promoting rhizobacterial (PGPR) strain Priestia endophytica SK1 isolated from fenugreek rhizospheric soil, which increased biomass and metabolite content in plants grown under saline stress. SK1 bacterial application induced nodule formation and enhanced nitrogen and phosphorus content under salt (100 mM NaCl) stress as compared to control plants. H2O2 production and lipid peroxidation as a measure of stress were observed high in control plants, while a reduction in these parameters was observed in plants inoculated with SK1. In addition, a significant effect was found on the phenolic compounds and trigonelline content in fenugreek plant inoculated with SK1 bacterium. An increased trigonelline content of about 54% over uninoculated control was recorded under salt stress.

CONCLUSION

The results of this study revealed that application of salt tolerant PGPR strain P. endophytica SK1 induced nitrogen fixation machinery that leads to alleviate salt stress and improved the biosynthesis of trigonelline content in fenugreek.

SIGNIFICANCE OF THE STUDY

This study extends our understanding on significance of rhizosphere microbiome and their beneficial role in plant health under environmental stress to promote agro-eco-farming practices.

Emerging Molecular Tools for Engineering Phytomicrobiome

Microbial plant interaction plays a major role in the sustainability of plants. The understanding of phytomicrobiome interactions enables the gene-editing tools for the construction of the microbial consortia. In this interaction, microbes share several common secondary metabolites and terpenoid metabolic pathways with their host plants that ensure a direct connection between the microbiome and associated plant metabolome. In this way, the CRISPR-mediated gene-editing tool provides an attractive approach to accomplish the creation of microbial consortia. On the other hand, the genetic manipulation of the host plant with the help of CRISPR-Cas9 can facilitate the characterization and identification of the genetic determinants. It leads to the enhancement of microbial capacity for more trait improvement. Many plant characteristics like phytovolatilization, phytoextraction, phytodesalination and phytodegradation are targeted by these approaches. Alternatively, chemical communications by PGPB are accomplished by the exchange of different signal molecules. For example, quorum-sensing is the way of the cell to cell communication in bacteria that lead to the detection of metabolites produced by pathogens during adverse conditions and also helpful in devising some tactics towards understanding plant immunity. Along with quorum-sensing, different volatile organic compounds and N-acyl homoserine lactones play a significant role in cell to cell communication by microbe to plant and among the plants respectively. Therefore, it is necessary to get details of all the significant approaches that are useful in exploring cell to cell communications. In this review, we have described gene-editing tools and the cell to cell communication process by quorum-sensing based signaling. These signaling processes via CRISPR- Cas9 mediated gene editing can improve the microbe-plant community in adverse climatic conditions.