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The overlapping regulation and effects of various stress response pathways in bacteria have been a major subject of study for several decades. This work examines the mechanisms by which a laboratory-acquired mutation in the rpoB gene conferring antibiotic tolerance also improves salt tolerance in Escherichia coli , an important pathogen of the human gut. We demonstrate that the rpoB mutation mimics the effects of multiple stress response pathways on gene expression and that pre-activation of these responses is critical for conferring hyperosmotic shock tolerance. These findings significantly advance our understanding of the genetic mechanisms controlling salt tolerance in bacteria and implicate the stringent response as one factor capable of conferring salt tolerance independent of the general stress response. Furthermore, these findings highlight the intricate connections between salt tolerance and other stress response pathways.

Euryhaline species exhibit significant adaptability to different salinities. This study elucidates how a single-celled euryhaline eukaryote navigates both transient and sustained salinity shifts at the molecular level. Comparative genomic analysis revealed that this organism expanded 195 gene families involved in ion transport and stress response. Transcriptomic analysis revealed distinct molecular foundations that underpin its transient and sustained adaptation to salinity stress. For high salinity, it transiently activates membrane transport systems, while long-term adaptation focuses on reprogramming metabolism to optimize energy use. In response to low salinity, the short-term response involves hydrolyzing intracellular materials, followed by the long-term activation of protective mechanisms. Additionally, alternative splicing fine-tunes genes involved in signaling and transport. These findings reveal unique genetic and cellular adaptation to salinity fluctuations in unicellular eukaryotes and establish a valuable resource for future functional investigations.

During osmotic changes of their environment, cells actively regulate their volume and plasma membrane tension that can passively change through osmosis. How tension and volume are coupled during osmotic adaptation remains unknown, as their quantitative characterization is lacking. Here, we performed dynamic membrane tension and cell volume measurements during osmotic shocks. During the first few seconds following the shock, cell volume varied to equilibrate osmotic pressures inside and outside the cell, and membrane tension dynamically followed these changes. A theoretical model based on the passive, reversible unfolding of the membrane as it detaches from the actin cortex during volume increase quantitatively describes our data. After the initial response, tension and volume recovered from hypoosmotic shocks but not from hyperosmotic shocks. Using a fluorescent membrane tension probe (fluorescent lipid tension reporter [Flipper-TR]), we investigated the coupling between tension and volume during these asymmetric recoveries. Caveolae depletion and pharmacological inhibition of ion transporters and channels, mTORCs, and the cytoskeleton all affected tension and volume responses. Treatments targeting mTORC2 and specific downstream effectors caused identical changes to both tension and volume responses, their coupling remaining the same. This supports that the coupling of tension and volume responses to osmotic shocks is primarily regulated by mTORC2.

Abiotic stresses, including drought and salinity, trigger a complex osmotic-stress and abscisic acid (ABA) signal transduction network. The core ABA signalling components are snf1-related protein kinase2s (SnRK2s), which are activated by ABA-triggered inhibition of type-2C protein-phosphatases (PP2Cs). SnRK2 kinases are also activated by a rapid, largely unknown, ABA-independent osmotic-stress signalling pathway. Here, through a combination of a redundancy-circumventing genetic screen and biochemical analyses, we have identified functionally-redundant MAPKK-kinases (M3Ks) that are necessary for activation of SnRK2 kinases. These M3Ks phosphorylate a specific SnRK2/OST1 site, which is indispensable for ABA-induced reactivation of PP2C-dephosphorylated SnRK2 kinases. ABA-triggered SnRK2 activation, transcription factor phosphorylation and SLAC1 activation require these M3Ks in vitro and in plants. M3K triple knock-out plants show reduced ABA sensitivity and strongly impaired rapid osmotic-stress-induced SnRK2 activation. These findings demonstrate that this M3K clade is required for ABA- and osmotic-stress-activation of SnRK2 kinases, enabling robust ABA and osmotic stress signal transduction. SnRK2 kinases activate abiotic stress responses in plants following ABA-dependent phosphatase inhibition or ABA-independent osmotic stress signalling. Here Takahashi et al. show that MAPKK-kinases phosphorylate and activate SnRK2s thus enabling robust ABA and osmotic stress signal transduction.

Understanding seedling responses of barley ( Hordeum vulgare L.) to water limitation benefits from integrated phenomics that quantify root–shoot dynamics under the osmotic component of drought. We profiled seven genotypes representing spring and winter growth types exposed to PEG 6000–simulated osmotic stress (− 0.5 and − 0.7 MPa, up to 9 days). A low-cost, high-resolution pipeline (flatbed scanning with image analysis) quantified root length, root diameter, and shoot length; shoot osmotic potential was derived from vapor-pressure osmometry (osmolality). Relative to the corresponding control (100%), winter seedlings tended to retain more root length than spring seedlings: at − 0.5 MPa, 51.9% (spring) vs. 63.3% (winter), and at − 0.7 MPa, 33.3% vs. 42% (means across the experiment). Root diameter retention was 98.3% (spring) and 91.4% (winter) at − 0.5 MPa, and 96.3% and 89.7% at − 0.7 MPa. Shoot length retention was 60.7% (spring) and 71.2% (winter) at − 0.5 MPa, and 27.3% and 32.4% at − 0.7 MPa. Shoot osmotic potential (MPa) showed a strong treatment effect ( p  < 0.001) but no significant spring–winter differences within any level (control: −0.46 spring vs. −0.49 winter; −0.5 MPa: −0.88 spring vs. −0.82 winter; −0.7 MPa: −0.80 spring vs. −0.79 winter), while individual genotypes differed in the magnitude of osmotic potential shifts, indicating substantial genotype-dependent variation. These hypothesis-generating results highlight contrasting seedling response patterns among growth types and genotypes and motivate further testing of facultative genotypes combining desirable trait profiles. The workflow demonstrates how accessible phenomics can resolve seedling-level trait patterns under osmotic stress and provides a foundation for field validation and genetic dissection toward improved resilience.

SNF1-related protein kinases 2 (SnRK2s) are key regulators governing the plant adaptive responses to osmotic stresses, such as drought and high salinity. Subclass III SnRK2s function as central regulators of abscisic acid (ABA) signalling and orchestrate ABA-regulated adaptive responses to osmotic stresses. Seed plants have acquired other types of osmotic stress-activated but ABA-unresponsive subclass I SnRK2s that regulate mRNA decay and promote plant growth under osmotic stresses. In contrast to subclass III SnRK2s, the regulatory mechanisms underlying the rapid activation of subclass I SnRK2s in response to osmotic stress remain elusive. Here, we report that three B4 Raf-like MAP kinase kinase kinases (MAPKKKs) phosphorylate and activate subclass I SnRK2s under osmotic stress. Transcriptome analyses reveal that genes downstream of these MAPKKKs largely overlap with subclass I SnRK2-regulated genes under osmotic stress, which indicates that these MAPKKKs are upstream factors of subclass I SnRK2 and are directly activated by osmotic stress. SnRK2 protein kinases play key roles in signaling during plant responses to abiotic stress. Here Soma et al . report three Arabidopsis Raf-like MAP kinase kinase kinases phosphorylate and activate a subclass of SnRK2s that rapidly respond to osmotic stress independently of ABA signaling.

Salinity is a significant environmental factor affecting physiological processes in plants. This study monitors the effect of salt stress induced by the NaCl solution (0 – deionized water; 50, 100, 200, 300 mmol/L) in rocket (Eruca sativa (L.) Mill.) cv. Astro over the course of 50 days. Salt stress significantly affected the monitored parameters. The osmotic potential decreased with increasing NaCl concentrations, while relative water content decrease did not take place until 200 mmol/L NaCl. Compared to the control group, transpiration (E) decreased at the concentration of 50 mmol/L NaCl and stomatal conductance (gs) and net photosynthetic rate (Pn) decreased at 100 mmol/L NaCl. Further increase of salt concentrations did not affect Pn and no significant differences gs, E and substomatal concentration CO2 were measured between the concentrations of 200 and 300 mmol/L NaCl. A decrease of Fv/Fm took place from the concentration of 100 mmol/L NaCl, while differences between 200 and 300 mmol/L NaCl were also not significant. The obtained results therefore prove the tolerance of the E. sativa cv. Astro to salt stress.

Understanding the mechanisms regulating root development under drought conditions is an important question for plant biology and world agriculture. We examine the effect of osmotic stress on abscisic acid (ABA), cytokinin and ethylene responses and how they mediate auxin transport, distribution and root growth through effects on PIN proteins. We integrate experimental data to construct hormonal crosstalk networks to formulate a systems view of root growth regulation by multiple hormones. Experimental analysis shows: that ABA-dependent and ABA-independent stress responses increase under osmotic stress, but cytokinin responses are only slightly reduced; inhibition of root growth under osmotic stress does not require ethylene signalling, but auxin can rescue root growth and meristem size; osmotic stress modulates auxin transporter levels and localization, reducing root auxin concentrations; PIN1 levels are reduced under stress in an ABA-dependent manner, overriding ethylene effects; and the interplay among ABA, ethylene, cytokinin and auxin is tissue-specific, as evidenced by differential responses of PIN1 and PIN2 to osmotic stress. Combining experimental analysis with network construction reveals that ABA regulates root growth under osmotic stress conditions via an interacting hormonal network with cytokinin, ethylene and auxin.

Background The sucrose non-fermenting-1-related protein kinase 2 family (SnRK2s) unifies different abiotic stress signals in plants. To date, the functions of two rice SnRK2s, osmotic stress/ABA-activated protein kinase 1 (SAPK1) and SAPK2, have been unknown. We investigated their roles in response to salt stress by generating loss-of-function lines using the CRISPR/Cas9 system and by overexpressing these proteins in transgenic rice plants. Results Expression profiling revealed that SAPK1 and SAPK2 expression were strongly induced by drought, NaCl, and PEG treatment, but not by ABA. SAPK2 expression was highest in the leaves, followed by the roots, whereas SAPK1 was highest expressed in roots followed by leaves. Both proteins were localized to the nucleus and the cytoplasm. Under salt stress, sapk1, sapk2 and, in particular, sapk1/2 mutants, exhibited reduced germination rates, more severe growth inhibition, more distinct chlorosis, reduced chlorophyll contents, and reduced survival rates in comparison with the wild-type plants. In contrast, SAPK1- and SAPK2-overexpression lines had increased germination rates and reduced sensitivities to salt; including mild reductions in growth inhibition, reduced chlorosis, increased chlorophyll contents and improved survival rates in comparison with the wild-type plants. These results suggest that SAPK1 and SAPK2 may function collaboratively as positive regulators of salt stress tolerance at the germination and seedling stages. We also found that SAPK1 and SAPK2 affected the osmotic potential following salt stress by promoting the generation of osmotically active metabolites such as proline. SAPK1 and SAPK2 also improved reactive oxygen species (ROS) detoxification following salt stress by promoting the generation of ROS scavengers such as ascorbic acid, and by increasing the expression levels of proteins such as superoxide dismutase (SOD) and catalase (CAT). SAPK1 and SAPK2 may function collaboratively in reducing Na + toxicity by affecting the Na + distribution between roots and shoots, Na + exclusion from the cytoplasm, and Na + sequestration into the vacuoles. These effects may be facilitated through the expression of Na + -and K + -homeostasis-related genes. Conclusion SAPK1 and SAPK2 may function collaboratively as positive regulators of salt stress tolerance at the germination and seedling stages in rice. SAPK1 and SAPK2 may be useful to improve salt tolerance in crop plants.

Abstract Soil salinization, affecting 6.5% of arable land, deteriorates soil properties, reduces microbiota activity, hinders plant growth, and accelerates soil erosion. Excessive salt induces physiological drought and toxicity stress in plants, causing chlorosis, ion imbalances, and enzyme disruptions. This paper discusses microorganisms’ resistance mechanisms, plant responses to salt stress, and summarizes current knowledge on bacterial osmoprotectants and their functions. It also reviews emerging agrobiotechnological strategies using microbial osmoprotectants to remediate salinized soils and enhance plant growth and productivity under salt stress. Osmoprotectants stabilize proteins, buffer redox potential, and retain water, thus alleviating osmotic stress and promoting bacteria and plants growth. Their application improves soil properties by enhancing aggregate formation, water permeability, moisture content, cation exchange capacity, and ion availability. Despite extensive literature on the function of osmoprotectants, the knowledge about their role in soil environments and agrobiotechnology applications remains limited. This paper indicates proposed research perspectives, including discovering new osmoprotectants, their correlation with soil fertilization, interactions with the soil microbiome, and plant responses. It also identifies significant knowledge gaps in these areas, highlighting the need for further studies to consolidate existing data and assess the potential of this approach to enhance soil health and crop productivity in saline environments. This review explores microbial osmoprotectants as innovative agrobiotechnological tools to combat soil salinization, emphasizing their potential to improve soil health, enhance plant resilience, and address critical challenges in sustainable agriculture under salt stress.