A salt stress-activated GSO1-SOS2-SOS1 module protects the Arabidopsis root stem cell niche by enhancing sodium ion extrusion.

Soil salinity impairs plant growth reducing crop productivity. Toxic accumulation of sodium ions is counteracted by the Salt Overly Sensitive (SOS) pathway for Na+ extrusion, comprising the Na+ transporter SOS1, the kinase SOS2, and SOS3 as one of several Calcineurin-B-like (CBL) Ca2 + sensors. Here, we report that the receptor-like kinase GSO1/SGN3 activates SOS2, independently of SOS3 binding, by physical interaction and phosphorylation at Thr16. Loss of GSO1 function renders plants salt sensitive and GSO1 is both sufficient and required for activating the SOS2-SOS1 module in yeast and in planta. Salt stress causes the accumulation of GSO1 in two specific and spatially defined areas of the root tip: in the endodermis section undergoing Casparian strip (CS) formation, where it reinforces the CIF-GSO1-SGN1 axis for CS barrier formation; and in the meristem, where it creates the GSO1-SOS2-SOS1 axis for Na+ detoxification. Thus, GSO1 simultaneously prevents Na+ both from diffusing into the vasculature, and from poisoning unprotected stem cells in the meristem. By protecting the meristem, receptor-like kinase-conferred activation of the SOS2-SOS1 module allows root growth to be maintained in adverse environments.

Phosphatidic acid-regulated SOS2 controls sodium and potassium homeostasis in Arabidopsis under salt stress.

The maintenance of sodium/potassium (Na+ /K+ ) homeostasis in plant cells is essential for salt tolerance. Plants export excess Na+ out of cells mainly through the Salt Overly Sensitive (SOS) pathway, activated by a calcium signal; however, it is unknown whether other signals regulate the SOS pathway and how K+ uptake is regulated under salt stress. Phosphatidic acid (PA) is emerging as a lipid signaling molecule that modulates cellular processes in development and the response to stimuli. Here, we show that PA binds to the residue Lys57 in SOS2, a core member of the SOS pathway, under salt stress, promoting the activity and plasma membrane localization of SOS2, which activates the Na+ /H+ antiporter SOS1 to promote the Na+ efflux. In addition, we reveal that PA promotes the phosphorylation of SOS3-like calcium-binding protein 8 (SCaBP8) by SOS2 under salt stress, which attenuates the SCaBP8-mediated inhibition of Arabidopsis K+ transporter 1 (AKT1), an inward-rectifying K+ channel. These findings suggest that PA regulates the SOS pathway and AKT1 activity under salt stress, promoting Na+ efflux and K+ influx to maintain Na+ /K+ homeostasis.

Gamblers: An Antibiotic-Induced Evolvable Cell Subpopulation Differentiated by Reactive-Oxygen-Induced General Stress Response.

Antibiotics can induce mutations that cause antibiotic resistance. Yet, despite their importance, mechanisms of antibiotic-promoted mutagenesis remain elusive. We report that the fluoroquinolone antibiotic ciprofloxacin (cipro) induces mutations by triggering transient differentiation of a mutant-generating cell subpopulation, using reactive oxygen species (ROS). Cipro-induced DNA breaks activate the Escherichia coli SOS DNA-damage response and error-prone DNA polymerases in all cells. However, mutagenesis is limited to a cell subpopulation in which electron transfer together with SOS induce ROS, which activate the sigma-S (σS) general-stress response, which allows mutagenic DNA-break repair. When sorted, this small σS-response-"on" subpopulation produces most antibiotic cross-resistant mutants. A U.S. Food and Drug Administration (FDA)-approved drug prevents σS induction, specifically inhibiting antibiotic-promoted mutagenesis. Further, SOS-inhibited cell division, which causes multi-chromosome cells, promotes mutagenesis. The data support a model in which within-cell chromosome cooperation together with development of a "gambler" cell subpopulation promote resistance evolution without risking most cells.

The global RNA-RNA interactome of Klebsiella pneumoniae unveils a small RNA regulator of cell division.

The ubiquitous RNA chaperone Hfq is involved in the regulation of key biological processes in many species across the bacterial kingdom. In the opportunistic human pathogen Klebsiella pneumoniae, deletion of the hfq gene affects the global transcriptome, virulence, and stress resistance; however, the ligands of the major RNA-binding protein in this species have remained elusive. In this study, we have combined transcriptomic, co-immunoprecipitation, and global RNA interactome analyses to compile an inventory of conserved and species-specific RNAs bound by Hfq and to monitor Hfq-mediated RNA-RNA interactions. In addition to dozens of RNA-RNA pairs, our study revealed an Hfq-dependent small regulatory RNA (sRNA), DinR, which is processed from the 3' terminal portion of dinI mRNA. Transcription of dinI is controlled by the master regulator of the SOS response, LexA. As DinR accumulates in K. pneumoniae in response to DNA damage, the sRNA represses translation of the ftsZ transcript by occupation of the ribosome binding site. Ectopic overexpression of DinR causes depletion of ftsZ mRNA and inhibition of cell division, while deletion of dinR antagonizes cell elongation in the presence of DNA damage. Collectively, our work highlights the important role of RNA-based gene regulation in K. pneumoniae and uncovers the central role of DinR in LexA-controlled division inhibition during the SOS response.

Inverse regulation of SOS1 and HKT1 protein localization and stability by SOS3/CBL4 in Arabidopsis thaliana.

To control net sodium (Na+) uptake, Arabidopsis plants utilize the plasma membrane (PM) Na+/H+ antiporter SOS1 to achieve Na+ efflux at the root and Na+ loading into the xylem, and the channel-like HKT1;1 protein that mediates the reverse flux of Na+ unloading off the xylem. Together, these opposing transport systems govern the partition of Na+ within the plant yet they must be finely co-regulated to prevent a futile cycle of xylem loading and unloading. Here, we show that the Arabidopsis SOS3 protein acts as the molecular switch governing these Na+ fluxes by favoring the recruitment of SOS1 to the PM and its subsequent activation by the SOS2/SOS3 kinase complex under salt stress, while commanding HKT1;1 protein degradation upon acute sodic stress. SOS3 achieves this role by direct and SOS2-independent binding to previously unrecognized functional domains of SOS1 and HKT1;1. These results indicate that roots first retain moderate amounts of salts to facilitate osmoregulation, yet when sodicity exceeds a set point, SOS3-dependent HKT1;1 degradation switches the balance toward Na+ export out of the root. Thus, SOS3 functionally links and co-regulates the two major Na+ transport systems operating in vascular plants controlling plant tolerance to salinity.

The DNA damage response of Escherichia coli, revisited: Differential gene expression after replication inhibition.

In 1967, in this journal, Evelyn Witkin proposed the existence of a coordinated DNA damage response in Escherichia coli, which later came to be called the "SOS response." We revisited this response using the replication inhibitor azidothymidine (AZT) and RNA-Seq analysis and identified several features. We confirm the induction of classic Save our ship (SOS) loci and identify several genes, including many of the pyrimidine pathway, that have not been previously demonstrated to be DNA damage-inducible. Despite a strong dependence on LexA, these genes lack LexA boxes and their regulation by LexA is likely to be indirect via unknown factors. We show that the transcription factor "stringent starvation protein" SspA is as important as LexA in the regulation of AZT-induced genes and that the genes activated by SspA change dramatically after AZT exposure. Our experiments identify additional LexA-independent DNA damage inducible genes, including 22 small RNA genes, some of which appear to activated by SspA. Motility and chemotaxis genes are strongly down-regulated by AZT, possibly as a result of one of more of the small RNAs or other transcription factors such as AppY and GadE, whose expression is elevated by AZT. Genes controlling the iron siderophore, enterobactin, and iron homeostasis are also strongly induced, independent of LexA. We confirm that IraD antiadaptor protein is induced independent of LexA and that a second antiadaptor, IraM is likewise strongly AZT-inducible, independent of LexA, suggesting that RpoS stabilization via these antiadaptor proteins is an integral part of replication stress tolerance.

Molecular Basis of Lysis-Lysogeny Decisions in Gram-Positive Phages.

Temperate bacteriophages (phages) are viruses of bacteria. Upon infection of a susceptible host, a temperate phage can establish either a lytic cycle that kills the host or a lysogenic cycle as a stable prophage. The life cycle pursued by an infecting temperate phage can have a significant impact not only on the individual host bacterium at the cellular level but also on bacterial communities and evolution in the ecosystem. Thus, understanding the decision processes of temperate phages is crucial. This review delves into the molecular mechanisms behind lysis-lysogeny decision-making in Gram-positive phages. We discuss a variety of molecular mechanisms and the genetic organization of these well-understood systems. By elucidating the strategies used by phages to make lysis-lysogeny decisions, we can improve our understanding of phage-host interactions, which is crucial for a variety of studies including bacterial evolution, community and ecosystem diversification, and phage therapeutics.

Mycobacterial Mutagenesis and Drug Resistance Are Controlled by Phosphorylation- and Cardiolipin-Mediated Inhibition of the RecA Coprotease.

Infection with Mycobacterium tuberculosis continues to cause substantial human mortality, in part because of the emergence of antimicrobial resistance. Antimicrobial resistance in tuberculosis is solely the result of chromosomal mutations that modify drug activators or targets, yet the mechanisms controlling the mycobacterial DNA-damage response (DDR) remain incompletely defined. Here, we identify RecA serine 207 as a multifunctional signaling hub that controls the DDR in mycobacteria. RecA S207 is phosphorylated after DNA damage, which suppresses the emergence of antibiotic resistance by selectively inhibiting the LexA coprotease function of RecA without affecting its ATPase or strand exchange functions. Additionally, RecA associates with the cytoplasmic membrane during the mycobacterial DDR, where cardiolipin can specifically inhibit the LexA coprotease function of unmodified, but not S207 phosphorylated, RecA. These findings reveal that RecA S207 controls mutagenesis and antibiotic resistance in mycobacteria through phosphorylation and cardiolipin-mediated inhibition of RecA coprotease function.

Phosphorylation of RhoGDI1, a Rho GDP dissociation inhibitor, regulates root hair development in Arabidopsis under salt stress.

To ensure optimal growth, plants actively regulate their growth and development based on environmental changes. Among these, salt stress significantly influences growth and yield. In this study, we demonstrate that the growth of root hairs of salt-stressed Arabidopsis thaliana seedlings is regulated by the SALT OVERLY SENSITIVE 2 (SOS2)-GUANOSINE NUCLEOTIDE DIPHOSPHATE DISSOCIATION INHIBITOR 1 (RhoGDI1)-Rho GTPASE OF PLANTS 2 (ROP2) module. We show here that the kinase SOS2 is activated by salt stress and subsequently phosphorylates RhoGDI1, a root hair regulator, thereby decreasing its stability. This change in RhoGDI1 abundance resulted in a fine-tuning of polar localization of ROP2 and root hair initiation followed by polar growth, demonstrating how SOS2-regulated root hair development is critical for plant growth under salt stress. Our results reveal how a tissue-specific response to salt stress balances the relationship of salt resistance and basic growth.

Structural basis for regulation of SOS response in bacteria.

In response to DNA damage, bacterial RecA protein forms filaments with the assistance of DinI protein. The RecA filaments stimulate the autocleavage of LexA, the repressor of more than 50 SOS genes, and activate the SOS response. During the late phase of SOS response, the RecA filaments stimulate the autocleavage of UmuD and λ repressor CI, leading to mutagenic repair and lytic cycle, respectively. Here, we determined the cryo-electron microscopy structures of Escherichia coli RecA filaments in complex with DinI, LexA, UmuD, and λCI by helical reconstruction. The structures reveal that LexA and UmuD dimers bind in the filament groove and cleave in an intramolecular and an intermolecular manner, respectively, while λCI binds deeply in the filament groove as a monomer. Despite their distinct folds and oligomeric states, all RecA filament binders recognize the same conserved protein features in the filament groove. The SOS response in bacteria can lead to mutagenesis and antimicrobial resistance, and our study paves the way for rational drug design targeting the bacterial SOS response.

SOS1 and KSR1 modulate MEK inhibitor responsiveness to target resistant cell populations based on PI3K and KRAS mutation status.

KRAS is the most commonly mutated oncogene. Targeted therapies have been developed against mediators of key downstream signaling pathways, predominantly components of the RAF/MEK/ERK kinase cascade. Unfortunately, single-agent efficacy of these agents is limited both by intrinsic and acquired resistance. Survival of drug-tolerant persister cells within the heterogeneous tumor population and/or acquired mutations that reactivate receptor tyrosine kinase (RTK)/RAS signaling can lead to outgrowth of tumor-initiating cells (TICs) and drive therapeutic resistance. Here, we show that targeting the key RTK/RAS pathway signaling intermediates SOS1 (Son of Sevenless 1) or KSR1 (Kinase Suppressor of RAS 1) both enhances the efficacy of, and prevents resistance to, the MEK inhibitor trametinib in KRAS-mutated lung (LUAD) and colorectal (COAD) adenocarcinoma cell lines depending on the specific mutational landscape. The SOS1 inhibitor BI-3406 enhanced the efficacy of trametinib and prevented trametinib resistance by targeting spheroid-initiating cells in KRASG12/G13-mutated LUAD and COAD cell lines that lacked PIK3CA comutations. Cell lines with KRASQ61 and/or PIK3CA mutations were insensitive to trametinib and BI-3406 combination therapy. In contrast, deletion of the RAF/MEK/ERK scaffold protein KSR1 prevented drug-induced SIC upregulation and restored trametinib sensitivity across all tested KRAS mutant cell lines in both PIK3CA-mutated and PIK3CA wild-type cancers. Our findings demonstrate that vertical inhibition of RTK/RAS signaling is an effective strategy to prevent therapeutic resistance in KRAS-mutated cancers, but therapeutic efficacy is dependent on both the specific KRAS mutant and underlying comutations. Thus, selection of optimal therapeutic combinations in KRAS-mutated cancers will require a detailed understanding of functional dependencies imposed by allele-specific KRAS mutations.

Anti-mutagenic agent targeting LexA to combat antimicrobial resistance in mycobacteria.

Antimicrobial resistance (AMR) is a serious global threat demanding innovations for effective control of pathogens. The bacterial SOS response, regulated by the master regulators, LexA and RecA, contributes to AMR through advantageous mutations. Targeting the LexA/RecA system with a novel inhibitor could suppress the SOS response and potentially reduce the occurrence of AMR. RecA presents a challenge as a therapeutic target due to its conserved structure and function across species, including humans. Conversely, LexA which is absent in eukaryotes, can be potentially targeted, due to its involvement in SOS response that is majorly responsible for adaptive mutagenesis and AMR. Our studies combining bioinformatic, biochemical, biophysical, molecular, and cell-based assays present a unique inhibitor of mycobacterial LexA, wherein we show that the inhibitor interacts directly with the catalytic site residues of LexA of Mycobacterium tuberculosis (Mtb), consequently hindering its cleavage, suppressing SOS response thereby reducing mutation frequency and AMR.

Heterogeneity of SOS response expression in clinical isolates of Escherichia coli influences adaptation to antimicrobial stress.

In recent years, new evidence has shown that the SOS response plays an important role in the response to antimicrobials, with involvement in the generation of clinical resistance. Here we evaluate the impact of heterogeneous expression of the SOS response in clinical isolates of Escherichia coli on response to the fluoroquinolone, ciprofloxacin. In silico analysis of whole genome sequencing data showed remarkable sequence conservation of the SOS response regulators, RecA and LexA. Despite the genetic homogeneity, our results revealed a marked differential heterogeneity in SOS response activation, both at population and single-cell level, among clinical isolates of E. coli in the presence of subinhibitory concentrations of ciprofloxacin. Four main stages of SOS response activation were identified and correlated with cell filamentation. Interestingly, there was a correlation between clinical isolates with higher expression of the SOS response and further progression to resistance. This heterogeneity in response to DNA damage repair (mediated by the SOS response) and induced by antimicrobial agents could be a new factor with implications for bacterial evolution and survival contributing to the generation of antimicrobial resistance.

The Na+/H+ antiporter SALT OVERLY SENSITIVE 1 regulates salt compensation of circadian rhythms by stabilizing GIGANTEA in Arabidopsis.

The circadian clock is a timekeeping, homeostatic system that temporally coordinates all major cellular processes. The function of the circadian clock is compensated in the face of variable environmental conditions ranging from normal to stress-inducing conditions. Salinity is a critical environmental factor affecting plant growth, and plants have evolved the SALT OVERLY SENSITIVE (SOS) pathway to acquire halotolerance. However, the regulatory systems for clock compensation under salinity are unclear. Here, we show that the plasma membrane Na+/H+ antiporter SOS1 specifically functions as a salt-specific circadian clock regulator via GIGANTEA (GI) in Arabidopsis thaliana. SOS1 directly interacts with GI in a salt-dependent manner and stabilizes this protein to sustain a proper clock period under salinity conditions. SOS1 function in circadian clock regulation requires the salt-mediated secondary messengers cytosolic free calcium and reactive oxygen species, pointing to a distinct regulatory role for SOS1 in addition to its function as a transporter to maintain Na+ homeostasis. Our results demonstrate that SOS1 maintains homeostasis of the salt response under high or daily fluctuating salt levels. These findings highlight the genetic capacity of the circadian clock to maintain timekeeping activity over a broad range of salinity levels.

The intrinsically disordered linker in the single-stranded DNA-binding protein influences DNA replication restart and recombination pathways in Escherichia coli K-12.

Tetrameric single-stranded (ss) DNA-binding proteins (SSBs) stabilize ssDNA intermediates formed during genome maintenance reactions in Bacteria. SSBs also recruit proteins important for these processes through direct SSB-protein interactions, including proteins involved in DNA replication restart and recombination processes. SSBs are composed of an N-terminal oligomerization and ssDNA-binding domain, a C-terminal acidic tip that mediates SSB-protein interactions, and an internal intrinsically disordered linker (IDL). Deletions and insertions into the IDL are well tolerated with few phenotypes, although the largest deletions and insertions exhibit some sensitivity to DNA-damaging agents. To define specific DNA metabolism processes dependent on IDL length, ssb mutants that lack 16, 26, 37, or 47 residues of the 57-residue IDL were tested for synthetic phenotypes with mutations in DNA replication restart or recombination genes. We also tested the impact of integrating a fluorescent domain within the SSB IDL using an ssb::mTur2 insertion mutation. Only the largest deletion tested or the insertion mutation causes sensitivity in any of the pathways. Mutations in two replication restart pathways (PriA-B1 and PriA-C) showed synthetic lethalities or small colony phenotypes with the largest deletion or insertion mutations. Recombination gene mutations del(recBCD) and del(ruvABC) show synthetic phenotypes only when combined with the largest ssb deletion. These results suggest that a minimum IDL length is important in some genome maintenance reactions in Escherichia coli. These include pathways involving PriA-PriB1, PriA-PriC, RecFOR, and RecG. The mTur2 insertion in the IDL may also affect SSB interactions in some processes, particularly the PriA-PriB1 and PriA-PriC replication restart pathways.IMPORTANCEssb is essential in Escherichia coli due to its roles in protecting ssDNA and coordinating genome maintenance events. While the DNA-binding core and acidic tip have well-characterized functions, the purpose of the intrinsically disordered linker (IDL) is poorly understood. In vitro studies have revealed that the IDL is important for cooperative ssDNA binding and phase separation. However, single-stranded (ss) DNA-binding protein (SSB) variants with large deletions and insertions in the IDL support normal cell growth. We find that the PriA-PriB1 and PriA-C replication restart, as well as the RecFOR- and RecG-dependent recombination, pathways are sensitive to IDL length. This suggests that cooperativity, phase separation, or a longer spacer between the core and acidic tip of SSB may be important for specific cellular functions.

Molecular cloning and characterization of a salt overly sensitive3 (SOS3) gene from the halophyte Pongamia.

A high concentration of sodium (Na+) is the primary stressor for plants in high salinity environments. The Salt Overly Sensitive (SOS) pathway is one of the best-studied signal transduction pathways, which confers plants the ability to export too much Na+ out of the cells or translocate the cytoplasmic Na+ into the vacuole. In this study, the Salt Overly Sensitive3 (MpSOS3) gene from Pongamia (Millettia pinnata Syn. Pongamia pinnata), a semi-mangrove, was isolated and characterized. The MpSOS3 protein has canonical EF-hand motifs conserved in other calcium-binding proteins and an N-myristoylation signature sequence. The MpSOS3 gene was significantly induced by salt stress, especially in Pongamia roots. Expression of the wild-type MpSOS3 but not the mutated nonmyristoylated MpSOS3-G2A could rescue the salt-hypersensitive phenotype of the Arabidopsis sos3-1 mutant, which suggested the N-myristoylation signature sequence of MpSOS3 was required for MpSOS3 function in plant salt tolerance. Heterologous expression of MpSOS3 in Arabidopsis accumulated less H2O2, superoxide anion radical (O2-), and malondialdehyde (MDA) than wild-type plants, which enhanced the salt tolerance of transgenic Arabidopsis plants. Under salt stress, MpSOS3 transgenic plants accumulated a lower content of Na+ and a higher content of K+ than wild-type plants, which maintained a better K+/Na+ ratio in transgenic plants. Moreover, no development and growth discrepancies were observed in the MpSOS3 heterologous overexpression plants compared to wild-type plants. Our results demonstrated that the MpSOS3 pathway confers a conservative salt-tolerant role and provided a foundation for further study of the SOS pathway in Pongamia.

Genetic Susceptibility in Endothelial Injury Syndromes after Hematopoietic Cell Transplantation and Other Cellular Therapies: Climbing a Steep Hill.

Hematopoietic stem cell transplantation (HSCT) remains a cornerstone in the management of patients with hematological malignancies. Endothelial injury syndromes, such as HSCT-associated thrombotic microangiopathy (HSCT-TMA), veno-occlusive disease/sinusoidal obstruction syndrome (SOS/VOD), and capillary leak syndrome (CLS), constitute complications after HSCT. Moreover, endothelial damage is prevalent after immunotherapy with chimeric antigen receptor-T (CAR-T) and can be manifested with cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). Our literature review aims to investigate the genetic susceptibility in endothelial injury syndromes after HSCT and CAR-T cell therapy. Variations in complement pathway- and endothelial function-related genes have been associated with the development of HSCT-TMA. In these genes, CFHR5, CFHR1, CFHR3, CFI, ADAMTS13, CFB, C3, C4, C5, and MASP1 are included. Thus, patients with these variations might have a predisposition to complement activation, which is also exaggerated by other factors (such as acute graft-versus-host disease, infections, and calcineurin inhibitors). Few studies have examined the genetic susceptibility to SOS/VOD syndrome, and the implicated genes include CFH, methylenetetrahydrofolate reductase, and heparinase. Finally, specific mutations have been associated with the onset of CRS (PFKFB4, CX3CR1) and ICANS (PPM1D, DNMT3A, TE2, ASXL1). More research is essential in this field to achieve better outcomes for our patients.

SulA does not sequester FtsZ in Escherichia coli cells during the SOS response.

In Escherichia coli, the SulA protein is synthesized during the SOS response to arrest cell division. Two possible models of SulA action were proposed: the sequestration and the capping. In current paper, to clarify which model better reflects the SulA effect on cell division upon the SOS response, the FtsZ/SulA ratio was estimated inside cells based on fusion of both FtsZ and SulA to fluorescent protein mNeonGreen. This allowed to quantify this ratio by fluorescence microscopy as well as western blotting; moreover, the effect of SulA on FtsZ distribution patterns in cells was analyzed based on fluorescence microscopy images. The SulA concentration in cells under the SOS response was shown to be several times (about 10) lower than that of FtsZ. The effect of SulA was unequal to corresponding decrease in FtsZ concentration. These results are supported by uneven FtsZ distribution in cells under the SOS response. Together the results of current work indicate that the division arrest by SulA protein in E. coli cells could not be explained by the sequestration model.

Features of the DNA Escherichia coli RecN interaction revealed by fluorescence microscopy and single-molecule methods.

The SOS response is a condition that occurs in bacterial cells after DNA damage. In this state, the bacterium is able to reсover the integrity of its genome. Due to the increased level of mutagenesis in cells during the repair of DNA double-strand breaks, the SOS response is also an important mechanism for bacterial adaptation to the antibiotics. One of the key proteins of the SOS response is the SMC-like protein RecN, which helps the RecA recombinase to find a homologous DNA template for repair. In this work, the localization of the recombinant RecN protein in living Escherichia coli cells was revealed using fluorescence microscopy. It has been shown that the RecN, outside the SOS response, is predominantly localized at the poles of the cell, and in dividing cells, also localized at the center. Using in vitro methods including fluorescence microscopy and optical tweezers, we show that RecN predominantly binds single-stranded DNA in an ATP-dependent manner. RecN has both intrinsic and single-stranded DNA-stimulated ATPase activity. The results of this work may be useful for better understanding of the SOS response mechanism and homologous recombination process.

SOS2-AFP2 module regulates seed germination by inducing ABI5 degradation in response to salt stress in Arabidopsis.

Soil salinity pose a significant challenge to global agriculture, threatening crop yields and food security. Understanding the salt tolerance mechanisms of plants is crucial for improving their survival under salt stress. AFP2, a negative regulator of ABA signaling, has been shown to play a crucial role in salt stress tolerance during seed germination. Mutations in AFP2 gene lead to increased sensitivity to salt stress. However, the underline mechanisms by which AFP2 regulates seed germination under salt stress remain elusive. In this study, we identified a protein interaction between AFP2 and SOS2, a Ser/Thr protein kinase known to play a critical role in salt stress response. Using a combination of genetic, biochemical, and physiological approaches, we investigated the role of the SOS2-AFP2 module in regulating seed germination under salt stress. Our findings reveal that SOS2 physically interacts with AFP2 and stabilizes it, leading to the degradation of the ABI5 protein, a negative transcription factor in seed germination under salt stress. This study sheds light on previously unknown connections within salt stress and ABA signaling, paving the way for novel strategies to enhance plant resilience against environmental challenges.