AUTHOR=Shi Li-Na , Lu Lan-Xiang , Ye Jian-Ren , Shi Hui-Min 

TITLE=The Endophytic Strain ZS-3 Enhances Salt Tolerance in Arabidopsis thaliana by Regulating Photosynthesis, Osmotic Stress, and Ion Homeostasis and Inducing Systemic Tolerance

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.820837

DOI=10.3389/fpls.2022.820837

ISSN=1664-462X

ABSTRACT=<p>Soil salinity is one of the main factors limiting agricultural development worldwide and has an adverse effect on plant growth and yield. To date, plant growth-promoting rhizobacteria (PGPR) are considered to be one of the most promising eco-friendly strategies for improving saline soils. The bacterium <italic>Bacillus megaterium</italic> ZS-3 is an excellent PGPR strain that induces growth promotion as well as biotic stress resistance and tolerance to abiotic stress in a broad range of host plants. In this study, the potential mechanisms of protection against salinity stress by <italic>B. megaterium</italic> ZS-3 in <italic>Arabidopsis thaliana</italic> were explored. Regulation by ZS-3 improved growth in <italic>A</italic>. <italic>thaliana</italic> under severe saline conditions. The results showed that ZS-3 treatment significantly increased the biomass, chlorophyll content and carotenoid content of <italic>A</italic>. <italic>thaliana</italic>. Compared to the control, the leaf area and total fresh weight of plants inoculated with ZS-3 increased by 245% and 271%, respectively; the chlorophyll a, chlorophyll b, and carotenoid contents increased by 335%, 146%, and 372%, respectively, under salt stress. Physiological and biochemical tests showed that ZS-3 regulated the content of osmotic substances in plants under salt stress. Compared to the control, the soluble sugar content of the ZS-3-treated group was significantly increased by 288%, while the proline content was significantly reduced by 41.43%. Quantification of Na<sup>+</sup> and K<sup>+</sup> contents showed that ZS-3 treatment significantly reduced Na<sup>+</sup> accumulation and increased the K<sup>+</sup>/Na<sup>+</sup> ratio in plants. ZS-3 also isolated Na<sup>+</sup> in vesicles by upregulating <italic>NHX1</italic> and <italic>AVP1</italic> expression while limiting Na<sup>+</sup> uptake by downregulating <italic>HKT1</italic>, which protected against Na<sup>+</sup> toxicity. Higher levels of peroxidase and catalase activity and reduced glutathione were detected in plants inoculated with ZS-3 compared to those in uninoculated plants. In addition, it was revealed that ZS-3 activates salicylic acid (<italic>NPR1</italic> and <italic>PR1</italic>) and jasmonic acid/ethylene (<italic>AOS</italic>, <italic>LOX2</italic>, <italic>PDF1.2</italic>, and <italic>ERF1</italic>) signaling pathways to induce systemic tolerance, thereby inducing salt tolerance in plants. In conclusion, the results of this study indicate that ZS-3 has the potential to act as an environmentally friendly salt tolerance inducer that can promote plant growth in salt-stressed environments.</p>