# Deciphering the Salt Tolerance Mechanisms of the Endophytic Plant Growth-Promoting Bacterium Pantoea sp. EEL5: Integration of Genomic, Transcriptomic, and Biochemical Analyses

## TL;DR

This study explores how a salt-tolerant bacterium survives in salty soil by removing sodium, boosting antioxidants, and conserving energy, offering insights for improving crop resilience.

## Contribution

The study reveals a multi-layered salt tolerance strategy in Pantoea sp. EEL5 through integrated genomic, transcriptomic, and biochemical analyses.

## Key findings

- EEL5 removes Na+ via extracellular adsorption and intracellular accumulation.
- Transcriptomic data show upregulation of genes for Na+ extrusion, antioxidants, and energy production.
- The bacterium conserves energy by reducing motility and accumulating protective solutes like betaine and GABA.

## Abstract

Soil salinization is a major threat to crops worldwide. Although some salt-tolerant growth-promoting bacteria (ST-PGPB) can confer crops tolerance to high salt, their own resilience mechanisms are not fully known. This study investigated the salt tolerance mechanisms of an endophytic ST-PGPB Pantoea sp. EEL5 isolated from Elytrigia elongata. Under salt stress, this bacterium actively removed Na+ from its cells, enhanced its antioxidant defenses, and accumulated protective molecules like betaine, glutamate, and GABA. It also increased energy production while conserving resources by reducing its mobility. These coordinated changes allowed it to thrive under high-salt conditions. The findings reveal the multi-layered strategy behind ST-PGPB’s salt tolerance, offering a molecular basis for developing more effective microbial products to improve crop resilience in salty fields.

Soil salinization poses a significant threat to global agricultural productivity. Salt-tolerant plant growth-promoting bacteria (ST-PGPB) have shown great potential in enhancing crop resilience under saline stress, yet the molecular basis of their intrinsic tolerance remains incompletely understood. To address this, we employed an integrated genomic, transcriptomic, and biochemical approach to investigate the salt tolerance strategies of Pantoea sp. EEL5, an endophytic ST-PGPB isolated from Elytrigia elongata. The results demonstrated that EEL5 exhibited remarkable salt tolerance and efficiently removed Na+ via extracellular adsorption and intracellular accumulation. Genomic analysis identified key genes responsible for Na+ efflux, betaine synthesis and transport, and typical plant growth-promoting traits. Under salt stress, transcriptomic profiling revealed a marked upregulation of genes involved in Na+ extrusion, antioxidant enzymes, betaine biosynthesis and transport, arginine and proline catabolism, TCA cycle, and electron transport chain, concomitant with a downregulation of genes governing energy-intensive flagellar assembly and chemotaxis. These coordinated responses facilitated Na+ exclusion, enhanced antioxidant capacity, accumulated compatible solutes (betaine, glutamate, and GABA), increased energy production, and conserved energy via motility reduction, collectively conferring salt tolerance in EEL5. Our findings elucidate the multi-level salt adaptation mechanisms of EEL5 and provide a genetic foundation for a comprehensive understanding of ST-PGPB.