Biology subjects

Sobol, G.

Publications and source records attributed to Sobol, G..

5 recordsLinked to original sources

bioRxiv2026

The gac system integrates physical and chemical cues to promote plant root attachment

Plants host complex communities of microbes that are attached to root surfaces. While many studies have sampled mutant populations after prolonged incubation on roots to identify bacterial genes that enable long-term colonization, the molecular mechanisms governing the early stages root attachment remain less understood. Here, we developed an in vitro root culture system that enables controlled and scalable investigation of bacterial attachment to root tissue. We used this platform to perform a genome-wide screen for root attachment determinants in the plant-associated bacterium Pseudomonas protegens Pf-5. Our results reveal that the gacSA two-component system functions as a sensory integration hub for coordinating early root attachment. Mutations that disrupt gacS or gacA cause severe root attachment defects despite having no effect on abiotic surface attachment in standard biofilm assays. Mutation of flagellar assembly genes enhances root attachment by mimicking surface contact and activating the gac system. In parallel, chemical cues released by roots stimulate surface attachment in a gac dependent manner. By integrating these signals, the gac system activates cyclic di-GMP-mediated attachment programs that drive the transition from planktonic to sessile behavior required for root association. We build on this model to show that manipulating flagellar surface sensing enhances the competitive fitness of Pf-5 in the presence of a synthetic bacterial community, suggesting a strategy to improve the competitive fitness of beneficial microbes on crops. These findings establish a mechanistic framework linking surface sensing, global regulation, and root attachment in a beneficial rhizobacterium. ImportancePlant roots are covered with diverse microbes that strongly influence plant health. Growing in association with roots has many benefits, but how bacteria attach to root tissue remains poorly understood. We developed a system to study how a bacterium that improves plant growth called Pseudomonas protegens Pf-5 attaches to root tissue. We found that physical contact with the root surface and chemical cues released by roots both enhance attachment to root tissue. A sensory system called gacSA is responsible for integrating physical and chemical cues to activate a root attachment program. Variant bacteria that prematurely activate the gac system compete more effectively with other bacteria on roots, suggesting that the root attachment pathway we characterized could serve as a strategy to use beneficial bacteria in agriculture.

microbiology↗

bioRxiv2026

A Calcium-mediated signaling pathway modulates ion homeostasis via HKT1;1 during Arabidopsis seed germination under salt stress

Soil salinization severely constrains seedling establishment by disrupting cellular Na/K homeostasis. Calcium (Ca{superscript 2}) signaling contributes to the re-establishment of ion balance during early growth, yet the mechanisms linking Ca{superscript 2} perception to ion transport regulation remain unclear. Here, we identify a Ca{superscript 2}-responsive regulatory module in Arabidopsis thaliana comprising CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 6 (CAMTA6), the TYPE 2C PROTEIN PHOSPHATASE PP2C49, and the HIGH-AFFINITY K TRANSPORTER HKT1;1, and define their coordinated roles during germination under salt stress. Spatial promoter analyses revealed that NaCl induces CAMTA6 expression at cotyledon margins, while CaCl2 stimulates HKT1;1 transcription in the radicle, consistent with CAMTA6-mediated repression of HKT1;1. In camta6 mutants, PP2C49 expression expanded beyond its normal radicle-restricted domain, indicating CAMTA6-dependent spatial control. Promoter activation assays in planta demonstrated CAMTA6-dependent transactivation of the HKT1;1 and PP2C49 promoters. Treatment with the PP2C inhibitor sanguinarine enhanced germination under salinity in the wild type, but not in hkt1 nor in the salt-tolerant camta6 and pp2c49 mutants. Sanguinarine restricted CAMTA6 promoter activity to cotyledon margins, suppressed PP2C49 expression, and enhanced HKT1;1 accumulation in the radicle, collectively supporting improved Na/K balance. Transcriptome profiling further revealed additional Ca{superscript 2}-responsive PP2C genes under CAMTA6-dependent regulation. Together, these findings establish a Ca{superscript 2}-regulated transcriptional network coordinating ion homeostasis during germination and suggest strategies to support seedling performance in saline environments. Significance statementSalinity impairs germination largely by disrupting Na/K homeostasis, yet the signaling pathways that protect seedlings at this stage remain poorly defined. We identify a calcium-responsive regulatory mechanism that spatially coordinates transcriptional control of genes involved in ion transport during early development, providing a mechanistic basis for improving seedling establishment in saline soils.

plant biology↗

bioRxiv2024

PP2C phosphatase Pic14 negatively regulates tomato Pto/Prf-triggered immunity by inhibiting MAPK activation

Type 2C protein phosphatases (PP2Cs) are emerging as important regulators of plant immune responses, although little is known about how they might impact nucleotide-binding, leucine-rich repeat (NLR)-triggered immunity (NTI). We discovered that expression of the PP2C-immunity associated candidate 14 gene (Pic14) is induced upon activation of the Pto/Prf-mediated NTI response in tomato. Pto/Prf recognize the effector AvrPto translocated into plant cells by the pathogen Pseudomonas syringae pv. tomato (Pst) and activate a MAPK cascade and other responses which together confer resistance to bacterial speck disease. Pic14 encodes a PP2C with an N-terminal kinase-interacting motif (KIM) and a C-terminal phosphatase domain. Upon inoculation with Pst-AvrPto, Pto/Prf-expressing tomato plants with loss-of-function mutations in Pic14 developed less speck disease, specifically in older leaves, compared to wild-type plants. Transient expression of Pic14 in leaves of Nicotiana benthamiana and tomato inhibited cell death typically induced by Pto/Prf and the MAPK cascade members M3K and Mkk2. The cell death-suppressing activity of Pic14 was dependent on the KIM and the catalytic phosphatase domain. Pic14 inhibited M3K- and Mkk2-mediated activation of immunity-associated MAPKs and Pic14 was shown to be an active phosphatase that physically interacts with and dephosphorylates Mkk2 in a KIM-dependent manner. Together, our results reveal Pic14 as an important negative regulator of Pto/Prf-triggered immunity by interacting with and dephosphorylating Mkk2. SIGNIFICANCE STATEMENTPlant intracellular immune receptors, typically nucleotide-binding, leucine-rich repeat proteins (NLRs) such as the tomato Prf protein activate NLR-triggered immunity (NTI) in response to specific pathogen virulence proteins. This paper reveals how a protein phosphatase interacts with and dephosphorylates a key signaling component acting downstream of Pto/Prf, likely to moderate negative effects of NTI on growth or other plant processes.

plant biology↗

bioRxiv2024

Related PP2C phosphatases Pic3 and Pic12 negatively regulate immunity in tomato to Pseudomonas syringae

Type 2C protein phosphatases (PP2Cs) constitute a large family in most plant species but relatively few of them have been implicated in immunity. To identify and characterize PP2C phosphatases that affect tomato immunity, we used CRISPR/Cas9 to generate loss-of-function mutations in 11 PP2C-encoding genes whose expression is altered in response to immune elicitors or pathogens. We report that two closely related PP2C phosphatases, Pic3 and Pic12, are involved in regulating resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Loss-of-function mutations in Pic3 lead to enhanced resistance to Pst in older but not younger leaves, whereas such mutations in Pic12 resulted in enhanced resistance in both older and younger leaves. Overexpression of Pic3 and Pic12 proteins in leaves of Nicotiana benthamiana inhibited resistance to Pst and this effect was dependent on Pic3/12 phosphatase activity and an N-terminal palmitoylation motif associated with localization to the cell periphery. Pic3 but not Pic12 had a slight negative effect on flagellin-associated reactive oxygen species generation, although their involvement in the response to Pst appeared independent of flagellin. RNA-sequencing analysis of Rio Grande (RG)-PtoR wild-type plants and two independent RG-pic3 mutants revealed that the enhanced disease resistance in RG-pic3 older leaves is associated with increased transcript abundance of multiple defense related genes. RG-pic3/RG-pic12 double mutant plants exhibited stronger disease resistance than RG-pic3 or RG-pic12 single mutants. Together, our results reveal that Pic3 and Pic12 negatively regulate tomato immunity in an additive manner through flagellin-independent pathways.

plant biology↗

bioRxiv2022

Tomato brassinosteroid-signaling kinase Bsk830 is a component of flagellin signaling that regulates pre-invasion immunity

Detection of bacterial flagellin by the tomato receptors Flagellin sensing 2 (Fls2) and Fls3 triggers activation of pattern-triggered immunity (PTI). Tomato signaling components associated or downstream of flagellin receptors are largely unknown. We investigated the involvement of tomato brassinosteroid-signaling kinase 830 (Bsk830) in PTI triggered by flagellin perception. Bsk830 localized to the plasma membrane and interacted with Fls2 and Fls3. Consistent with a role in flagellin- induced signaling, CRISPR/Cas9-generated tomato bsk830 mutants were impaired in ROS accumulation induced by the flagellin-derived flg22 and flgII-28 peptides. In addition, bsk830 mutants developed larger populations of Pseudomonas syringae pv. tomato (Pst) strain DC3000 than wild-type plants, whereas no differences were observed in plants infected with the flagellin deficient Pst DC3000{Delta}fliC. bsk830 mutants failed to close stomata when infected with Pst DC3000 and Pseudomonas fluorescens, and were more susceptible to Pst DC3000 than wild-type plants when inoculated by dipping, but not by vacuum-infiltration, indicating involvement of Bsk830 in pre-invasion immunity. Analysis of gene expression profiles in bsk830 mutants detected a reduced number of differentially expressed genes and altered expression of jasmonic acid (JA)-related genes. In support of deregulation of JA response in bsk830 mutants, these plants were similarly susceptible to Pst DC3000 and to the Pst DC3118 strain, which is deficient in coronatine production, and more resistant to the necrotrophic fungus Botrytis cinerea following PTI activation. These results indicate that tomato Bsk830 is required for a subset of flagellin-triggered PTI responses and support a model in which Bsk830 negatively regulates JA signaling during PTI activation.

plant biology↗