Biology subjects

Testerink, C.

Publications and source records attributed to Testerink, C..

At least 19 recordsLinked to original sources

bioRxiv2026

Phytosulfokine signaling modulates salt stress responses and cell wall remodeling in Arabidopsis

Salinity severely impairs plant growth and development. Increasing evidence suggests that the cell wall (CW) plays a central role in salt stress acclimation, not only as a structural barrier but also as a dynamic sensor that activates downstream stress signaling pathways. To identify extracellular factors involved in cell wall remodeling and integrity signaling during salt stress, we performed a comparative proteomic analysis of the Arabidopsis seedling apoplast. Among the proteins that accumulated under salt stress, we focused on three members of the Subtilisin-Like Protease family (SBT1.1, SBT1.6, and SBT5.3), which have previously been implicated in the processing of signaling peptides and CW-associated proteins. Functional analyses revealed that sbt1.1 and sbt5.3 mutants exhibit enhanced lignin deposition under salt stress, suggesting altered CW remodeling during stress application. Given the established role of SBT1.1 in processing PHYTOSULFOKINE (PSK) peptides, we investigated the involvement of PSK signaling in salt stress responses. Mutants lacking the two PSK RECEPTORS (pskr1 pskr2) displayed reduced growth and increased lignification under salt treatment. Exogenous application of PSK attenuated salt-induced responses, including MITOGEN ACTIVATED PROTEIN KINASE 6 (MPK6) phosphorylation, salt stress marker gene expression, and lignin accumulation, ultimately promoting root elongation under salt stress. Furthermore, PSK treatment mitigated salt-induced changes in CW composition. In cell wall integrity (CWI) mutants, PSK treatment failed to restore wild-type root growth under salt stress and induced a pronounced root bending phenotype in fer-4, indicating that CWI signaling influences PSK-mediated root growth responses. Together, these results support a role for PSK signaling in modulating CW-associated responses to salinity stress in Arabidopsis.

plant biology↗

bioRxiv2026

The SAUERKRAUT transposable element acceleratesArabidopsis floral transition

Salt stress alters plant development, including the floral transition, but regulation of timing of flowering by salt is poorly understood at the molecular level. To identify genetic loci regulating the floral transition under high soil salinity, we performed a genome-wide association study (GWAS) in Arabidopsis thaliana and identified natural variation at the UGT74E1-UGT74E2-BT3 (UUB) locus that correlates with bolting time specifically in response to salt stress. Genetic analysis revealed BT3 as a novel repressor of the floral transition in control conditions. Similarly, the putative IBA glycosylases UGT74E1 & UGT74E2 delay the floral transition in control conditions. Furthermore, we identified that IBA homeostasis regulators TOB1 and ECH2/IBR10 play a key role in the floral transition, and that ECH2/IBR10 are required for the early flowering phenotype of the ugt74e1/ugt74e2 double mutant, indicating that UGT74E1 & UGT74E2 delay flowering by altering IBA homeostasis. A pangenome analysis of the UUB locus revealed variation in the occurrence of the DNA transposon SAUERKRAUT (SKRT). CRISPR-mediated SKRT deletion in Col-0 affected gene expression both within and outside the UUB locus and caused a salt-dependent delayed floral transition. The delayed bolting phenotype of the skrt-2 mutant also depends on ECH2/IBR10 function, indicating that SKRT accelerates the floral transition by altering IBA homeostasis. Finally, targeted demethylation of SKRT resulted in delayed floral transition under salt stress. Taken together, our data show a role for SKRT and its DNA methylation levels in the salt-dependent bolting time response in Arabidopsis, revealing a novel molecular mechanism to control flowering in adverse conditions.

plant biology↗

bioRxiv2026

Pseudomonas volatiles shape the root transcriptome and microbiome to promote plant growth under drought

O_LIVolatile organic compounds (VOCs) emitted by soil bacteria influence interactions with other soil microbes and with plant roots. While their potential as plant-growth promoters is well recognized, their role in promoting plant resilience to abiotic stress and the underlying molecular mechanisms remains poorly understood. Here, we investigate the role of Pseudomonas VOCs in enhancing plant resilience to drought stress. C_LIO_LIArabidopsis thaliana plants were exposed to VOCs emitted by Pseudomonas strains under both control and osmotic-stress conditions. VOC exposure generally enhanced plant growth, and this effect was even more pronounced under both drought and salt stress. Transcriptomic analysis revealed that VOC exposure modulates key stress-responsive pathways, including those related to abscisic acid biosynthesis and signalling, sugar transport, iron uptake, aliphatic glucosinolate biosynthesis, and plant defences. Using Arabidopsis mutants, we identified abscisic acid and aliphatic glucosinolates as important components in mediating the plant response to VOCs. SWEET11/12 sugar transporters and ABA signaling genes were downregulated by VOCs exposure, in order to allow for a positive regulation of lateral root numbers (in case of SWEET genes) and plant growth in general under drought stress. In summary, using metabolomics, transcriptomics and functional analysis, we showed a negative cross-talk between the effects of VOCs on plant growth and glucosinolate production, whereas a positive interaction was observed between the biosynthesis of coumarins and VOCs. C_LIO_LINotably, VOCs also improved drought tolerance in soil-grown Brassica oleracea plants. We showed that VOC treatment altered the root-associated microbiome under drought, leading to a community composition more similar to that of well-watered plants. C_LIO_LIOur results show that Pseudomonas emitted VOCs can promote plant growth under drought conditions, linked to root transcriptional reprogramming and direct or indirect microbiome modulation. C_LI

plant biology↗

bioRxiv2025

Salt stress disrupts local auxin and COP1 gradients in Arabidopsis apical hooks

Seedling establishment is highly sensitive to environmental cues, with light serving as a principal regulator. In darkness, seedlings enter skotomorphogenesis, marked by hypocotyl elongation and apical hook formation, which helps seedlings emerge from the soil to reach the light. Here, we show that salinity impairs soil emergence of Arabidopsis thaliana seedlings by inducing a partially photomorphogenic like phenotype in darkness, characterized by reduced apical hook curvature. Within the hook, salt stress diminished differential epidermal cell elongation required to drive hook bending, and reduced both the auxin signalling maximum and PIN3 abundance on the concave side of the hook. Transcriptome analysis revealed that salt and osmotic stresses directly alter organ-specific transcriptional profiles, including the NaCl-mediated repression of B-BOX DOMAIN PROTEIN 28 (BBX28) in hooks and cotyledons. Under control conditions, BBX28 protein accumulated asymmetrically across the hook, but this pattern was lost under salinity. Notably, the ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) exhibited an opposite gradient to BBX28, which was similarly disrupted by salt stress or by the inhibition of polar auxin transport, presenting auxin as an upstream regulator of COP1 spatial distribution. Together, these findings establish COP1 asymmetry as a novel feature of the apical hook, indicating that spatial regulation--not just absolute levels--shapes COP1 function, and reveal how salinity disrupts hormonal, transcriptional and protein networks to compromise seedling establishment under stress. Significance StatementSeedling establishment is a critical developmental transition that contributes to survival in the local environment. While light is the primary cue driving de-etiolation, how abiotic stress shapes early development in darkness remains unclear. We show that salinity induces a photomorphogenic-like response in dark-grown Arabidopsis thaliana seedlings, disrupting apical hook formation and soil emergence. This response involves disrupted asymmetrical epidermal cell elongation and auxin signalling, repression of B-BOX DOMAIN PROTEIN 28 (BBX28), and loss of a previously unrecognized spatial gradient of the key light regulator COP1 across the apical hook. Our discovery that COP1 is spatially regulated and disrupted by stress, reveals a new dimension of light signalling and developmental control, highlighting how environmental stress constrains seedling establishment.

plant biology↗

bioRxiv2024

Quantitative light element (sodium and potassium) profiling in plant tissues using monochromatic X-ray fluorescence analysis

Accurately determining the elemental composition of plant tissues is essential for physiological studies on plant stress, including salinity tolerance. However, high-throughput routine analysis of light elements (range of sodium to calcium) in plant samples is challenging due to the need for complete sample dissolution and expensive inductively coupled plasma-mass-spectrometry (ICP-MS) analysis. Lower costs method (ion chromatography, ion selective electrodes) exists, but also require sample dissolution and lack sensitivity for very small samples (<10 mg). This study reports on a new method for the quantitative analysis of light elements in plant tissues using monochromatic X-ray fluorescence (XRF) instrumentation and innovative sample preparation and mounting. We used this approach to assess elemental uptake, distribution, and accumulation in Arabidopsis thaliana and Oryza sativa plants subjected to salt stress. The method can be used on samples as small as 1 mg making it suitable for small Arabidopsis thaliana plants. We systematically evaluated different sample preparations methods, repeatability, and measurement times to confirm the robustness of the technique. The results show that the monochromatic XRF method delivers rapid, non-destructive, and extraction-free analysis, strongly correlating with ICP-MS acquired data. As such, the monochromatic XRF method is a reliable and efficient alternative for studying salinity tolerance ideally suited for investigating elemental composition of early plant developmental stages, offering new possibilities for research into early stimuli sensing, perception and nutrient efficiency.

plant biology↗

bioRxiv2024

Potato cultivars use different root physiological and molecular mechanisms to acclimate to salt stress

O_LISoil salinity induces osmotic stress and ion toxicity in plants, detrimentally affecting their growth and development. Potato (Solanum tuberosum) faces yield reductions due to salt stress. The mechanisms of salt stress resilience, especially in adventitious roots, remain unknown. C_LIO_LIWe investigated the resilience of three potato cultivars - Desiree, Innovator, and Mozart - by studying their physiological and transcriptomic responses to salt stress. C_LIO_LIOur findings reveal that under salt stress, the growth of stolons and stolon node roots is similarly reduced unlike tubers, even though they are physically connected. Surprisingly, tubers accumulate Cl- but not Na+ under salt stress, suggesting an active Na+ exclusion mechanism. Innovator showed the lowest suberin and lignin deposition before salt stress and higher K+ leakage, leading to a stronger initial stress response with high ABA content and a distinct transcriptomic pattern. Nevertheless, Innovator was the most resilient, displaying lower growth, salt-tolerance index and tuber yield reduction. Transcriptomic analysis revealed several K+/Na+ channel genes which might regulate ions homeostasis during salt stress, in particular in Innovator. C_LIO_LIAltogether, we conclude that acclimation ability, rather than initial protection of roots against salt, prevails in long term salt-stress resilience of potato. C_LI

plant biology↗

bioRxiv2024

Characterization of a major QTL for sodium accumulation in tomato shoot

Soil salinity is a serious concern for tomato culture, affecting both yield and quality parameters. Although some genes involved in tomato salt tolerance have been identified, their genetic diversity has been rarely studied. In the present study, we assessed salt tolerance-related traits at juvenile and adult stages in a large core collection and identified salt tolerance QTLs by genome-wide association study (GWAS). The results suggested that a major QTL is involved in leaf sodium accumulation at both physiological stages. We were able to identify the underlying candidate gene, a well-known sodium transporter, called SlHKT1.2. We showed that an eQTL for the expression of this gene colocalized with the sodium content QTL. A polymorphism putatively responsible for its variation was identified in the gene promoter. Finally, to extend the applicability of these results, we carried out the same analysis on a test-cross panel composed of the core collection crossed with a distant line. The results indicated that the identified QTL retained its functional impact even in a hybrid genetic context: this paves the way for its use in breeding programs aimed at improving salinity tolerance in tomato cultivars. Summary statementThe genetic diversity of sodium accumulation in tomato shoot under salt stress is associated with an expression QTL of SlHKT1.2. This gene, already identified as involved in tomato salinity tolerance, has been differentially selected during domestication and is of interest for the development of salinity-tolerant varieties.

plant biology↗

bioRxiv2024

Natural variation in salt-induced changes in root:shoot ratio reveals SR3G as a negative regulator of root suberization and salt resilience in Arabidopsis

Soil salinity is one of the major threats to agricultural productivity worldwide. Salt stress exposure alters root and shoot growth rates, thereby affecting overall plant performance. While past studies have extensively documented the effect of salt stress on root elongation and shoot development separately, here we take an innovative approach by examining the coordination of root and shoot growth under salt stress conditions. Utilizing a newly developed tool for quantifying the root:shoot ratio in agar-grown Arabidopsis seedlings, we found that salt stress results in a loss of coordination between root and shoot growth rates. We identify a specific gene cluster encoding domain-of-unknown-function 247 (DUF247), and characterize one of these genes as Salt Root:shoot Ratio Regulator Gene (SR3G). Further analysis elucidates the role of SR3G as a negative regulator of salt stress tolerance, revealing its function in regulating shoot growth, root suberization, and sodium accumulation. We further characterize that SR3G expression is modulated by WRKY75 transcription factor, known as a positive regulator of salt stress tolerance. Finally, we show that the salt stress sensitivity of wrky75 mutant is completely diminished when it is combined with sr3g mutation. Together, our results demonstrate that utilizing root:shoot ratio as an architectural feature leads to the discovery of new stress resilience gene. The studys innovative approach and findings not only contribute to our understanding of plant stress tolerance mechanisms but also open new avenues for genetic and agronomic strategies to enhance crop environmental resilience.

plant biology↗

bioRxiv2023

Abscisic acid signaling gates salt-specific responses of plant roots

Soil salinity presents a dual challenge for plants, involving both osmotic and ionic stress. In response, plants deploy distinct yet interconnected mechanisms to cope with these facets of salinity stress. In this investigation, we observed a substantial overlap in the salt (NaCl)-induced transcriptional responses of Arabidopsis roots with those triggered by osmotic stress or the plant stress hormone abscisic acid (ABA), as anticipated. Notably, a specific cluster of genes responded uniquely to sodium (Na+) ions. Surprisingly, expression of sodium-induced genes exhibited a negative correlation with the ABA response and preceded the activation of genes induced by the osmotic stress component of salt. Elevated exogenous ABA levels resulted in the complete abolition of sodium-induced responses. Consistently, ABA signalling mutants displayed prolonged sodium-induced gene expression, coupled with increased root cell damage under high salinity conditions. Moreover, ABA signalling mutants were unable to redirect root growth to avoid high sodium concentrations and failed to contain their root cell swelling in the presence of elevated salt levels. In summary, our findings unveil an unexpected and pivotal role for ABA signaling in mitigating cellular damage induced by salinity stress and modulating sodium-specific responses in plant roots.

plant biology↗

bioRxiv2023

Warm temperature and mild water stress cooperatively promote root elongation

Warm temperatures have a dramatic effect on plant development. In shoots, stems elongate, and leaves are raised in a developmental programme called thermomorphogenesis. This results in enhanced leaf cooling capacity1. Thermomorphogenesis is tightly intertwined with light signalling pathways. The level of integration is so high that it has been proposed that shoot temperature sensing may have evolved from the co-option of an existing light signalling pathway during the colonisation of land by plants2. Roots also undergo thermomorphogenesis, but the mechanism by which this occurs is less well understood. Main root elongation is enhanced at warm temperatures, and this response is independent of many of the light and temperature signalling components of the shoot3. Roots develop in darkness and so it is a reasonable assumption that root temperature signalling is not through modulation of light signalling. It was recently speculated that due to the close correlation between warm temperature and soil moisture content, root temperature signalling could feasibly be related to water availability signals2. In this study we tested the interaction between temperature and water availability signalling in plant roots. We found that these environmental factors co-operatively enhance main root elongation. This interaction effect was dependent on SUCROSE NON-FERMENTING RELATED KINASE 2.2 (SnRK2.2) and SnRK2.3 and the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). We found that SnRK2.2 / 2.3 and COP1 have opposite effects on the stability of the transcription factor ELONGATED HYPOCOTYL 5 (HY5) in elongation zone hair cells. The stability of HY5 in these cell types generally corresponded to the degree of root elongation seen in each mutant background. Our study reveals several molecular components of root thermomorphogenesis and highlights the importance of an integrative approach to plant environmental signalling. Our results may have direct implications for agricultural land management, especially as global climates become more unpredictable.

plant biology↗

bioRxiv2023

Antagonistic Regulation of Arabidopsis Leaf Senescence by SCOOP10 and SCOOP12 Peptides via MIK2 Receptor-Like Kinase

Leaf senescence plays a critical role in a plants overall reproductive success due to its involvement in nutrient remobilization and allocation. However, our current understanding of the molecular mechanisms controlling leaf senescence remains limited. In this study, we demonstrate that the receptor-like kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) functions as a negative regulator of leaf senescence. We report that the SERINE-RICH ENDOGENOUS PEPTIDES 10 and 12 (SCOOP10 and SCOOP12), previously known to physically interact with MIK2, compete with each other to control MIK2-dependent senescence mechanisms. We observed that increased expression of SCOOP10 or the application of exogenous SCOOP10 peptides accelerated leaf senescence in a MIK2-dependent manner. Conversely, SCOOP12 acted as a suppressor of MIK2-dependent senescence. Thus, the SCOOP10-MIK2 and the SCOOP12-MIK2 modules function antagonistically, allowing for fine-tuning the modulation of the leaf senescence process. Our research sheds light on the complex mechanisms underlying leaf senescence and provides valuable insights into the interplay between receptors, peptides, and the regulation of plant senescence.

plant biology↗

bioRxiv2023

CYP79B2 and CYP79B3 contribute to root branching through production of the auxin precursor indole-3-acetonitrile

Lateral root placement, outgrowth and density are influenced by environmental changes, including salinity stress. CYP79B2 and B3 are two cytochrome P450 enzymes previously identified as required for root architecture remodeling in salt. They produce iAOx, a metabolite that can be converted into indole glucosinolates (IGs), camalexin and indole-3-acetic acid (IAA), a type of auxin. We report here that lateral root appearance, induced by an auxin maximum in the bending zone after gravistimulation, is delayed in the absence of CYP79B2/B3. This delay traces back to a decrease in early lateral root growth after emergence, taking place before lateral roots are macroscopically visible. We measured gene transcripts and abundance of metabolites in the iAOx pathway in root segments that are forming lateral roots. Genes involved in tryptophane and IG biosynthesis were upregulated in cyp79b2/b3 mutants, suggesting a transcriptional feedback-loop. Salt stress was found to increase the expression of genes involved in IAN biosynthesis, a precursor of both IAA and camalexin, in the root during lateral root formation. Moreover, salt increases the concentration of IAN in tissue forming lateral roots in a CYP79B2/B3 dependent manner, but these changes in IAN did not coincide with altered IAA levels. Both the reduction in lateral root density under salt and the delayed lateral root appearance in cyp79b2/b3 knock-out mutants can be complemented by exogenous application of IAN. Our results reveal a role for the iAOx pathway in regulating the timing of lateral root appearance, allowing the modulation of lateral root density under salt stress.

plant biology↗

bioRxiv2023

Root branching in salt requires auxin-independent modulation of LBD16 function

Salinity stress constrains lateral root (LR) growth and severely impacts plant growth. Auxin signaling is indispensable for the regulation of LR formation. Nevertheless, the molecular mechanism of how salinity affects root auxin signaling and whether salt would steer alternative pathway(s) to regulate LR development is unknown. Here we show that the auxin-regulated transcription factor LATERAL ORGAN BOUNDARY DOMAIN (LBD)16, known as an essential player for LR development under control conditions, is regulated by an alternative non-canonical pathway under salinity. Salt represses auxin signaling but in parallel activates an upstream transcriptional activator of LBD16, ZINC FINGER OF ARABIDOPSIS THALIANA 6 (ZAT6). ZAT6 modulates the activity of LBD16 to contribute to downstream cell wall remodeling, and promotes LR development under salinity stress. Our study thus shows that root developmental plasticity in response to salt stress is achieved by integration of auxin-dependent repressive and salt-activated auxin-independent pathways converging on LBD16 to modulate root branching modulation under salinity.

plant biology↗

bioRxiv2023

Natural variation in salt-induced root growth phases and their contribution to root architecture plasticity

During salt stress, the root system architecture of a plant is important for survival. Different accessions of Arabidopsis thaliana have adopted different strategies in remodeling their root architecture during salt stress. Salt induces a multiphase growth response in roots, consisting of a stop phase, quiescent phase, recovery phase and eventually a new level of homeostasis. We explored natural variation in the length of and growth rate during these phases in both main and lateral roots and find that some accessions lack the quiescent phase. Using mathematical models and correlation-based network, allowed us to correlate dynamic traits to overall root architecture and discover that both the main root growth rate during homeostasis and lateral root appearance are the strongest determinants of overall root architecture. In addition, this approach revealed a trade-off between investing in main or lateral root length during salt stress. By studying natural variation in high-resolution temporal root growth using mathematical modeling, we gained new insights in the interactions between dynamic root growth traits and we identified key traits that modulate overall root architecture during salt stress. Summary statementBy studying natural variation in salt-induced root growth phases in Arabidopsis, we show that main root growth rate during homeostasis and lateral root appearance contribute most to root architecture and we reveal a trade-off between investing in main and lateral root growth during salt stress.

plant biology↗

bioRxiv2022

Mapping the adaptor protein complex interaction network in Arabidopsis identifies P34 as a common stability regulator

Adaptor protein (AP) complexes are evolutionarily conserved vesicle transport regulators that recruit coat proteins, membrane cargos and coated vesicle accessory proteins. Since in plants endocytic and post-Golgi trafficking intersect at the trans-Golgi network, unique mechanisms for sorting cargos of overlapping vesicular routes are anticipated. The plant AP complexes are part of the sorting machinery, but despite some functional information, their cargoes, accessory proteins, and regulation remain largely unknown. Here, by means of various proteomics approaches, we generated the overall interactome of the five AP and the TPLATE complexes in Arabidopsis thaliana. The interactome converged on a number of hub proteins, including the thus far unknown adaptin binding-like protein, designated P34. P34 interacted with the clathrin-associated AP complexes, controlled their stability and, subsequently, influenced clathrin-mediated endocytosis and various post-Golgi trafficking routes. Altogether, the AP interactome network offers substantial resources for further discoveries of unknown endomembrane trafficking regulators in plant cells.

plant biology↗

bioRxiv2022

Effective root responses to salinity stress include maintained cell expansion and carbon allocation

Acclimation of root growth is vital for plants to survive salt stress. Halophytes are great examples of plants that thrive under high salt concentrations but their salt tolerance mechanisms, especially those mediated by root responses, are still largely unknown. We compared root growth responses of the halophyte Schrenkiella parvula with its glycophytic relative species Arabidopsis thaliana under salt stress, and performed root transcriptomic analysis to identify differences in gene regulatory networks underlying their physiological responses. Primary root growth of S. parvula is less sensitive to salt compared with Arabidopsis. The root transcriptomic analysis of S. parvula revealed the induction of sugar transporters and genes regulating cell expansion and suberization under salt stress. 14C-labelled carbon partitioning analyses consistently showed that S. parvula had a higher incorporation rate of soluble sugars in roots under salt stress compared to Arabidopsis. Further physiological investigation revealed that S. parvula roots do not show a halotropic response and maintain root cell expansion and enhanced suberization even under severe salt stress. In summary, our study demonstrates that roots of S. parvula deploy multiple physiological and developmental adjustments under salt stress to maintain growth, providing new avenues to improve salt tolerance of plants using root-specific strategies.

plant biology↗

bioRxiv2022

Cell wall extensin arabinosylation is required for root directional response to salinity

Soil salinity is a major contributor to crop yield losses. To improve our understanding of root responses to salinity, we developed and exploit here a real-time salt-induced tilting assay (SITA). This method follows root growth upon both gravitropic and salt challenges, revealing that root bending upon tilting is modulated by salinity, but not by osmotic stress. Next, this salt-specific response was measured in 345 natural Arabidopsis accessions and we discovered a genetic locus, encoding for the cell-wall modifying enzyme EXTENSIN ARABINOSE DEFICIENT TRANSFERASE (ExAD), to be associated with root bending in salt. Extensins are a class of structural cell wall glycoproteins [hydroxyproline-rich glycoproteins (HRGPs)] which are post-translationally modified by O-glycosylation mostly in the form of hydroxyproline (Hyp)-arabinosylation. We show that salt induces ExAD-dependent Hyp-arabinosylation, influencing root bending responses and cell wall thickness. We report that roots of exad mutants, which lack extensin Hyp-Araf4 modifications, display increased root epidermal cell wall thickness and porosity and altered gravitropic root bending in salt, as well as a reduced salt avoidance response. Our results suggest that extensin modification via Hyp-arabinosylation represents a novel salt-specific cellular process that is required for the directional response of roots exposed to salinity.

plant biology↗

bioRxiv2020

Salinity stress-induced modification of pectin activates stress signaling pathways and requires HERK/THE and FER to attenuate the response

Soil salinity is an increasing worldwide problem for agriculture, affecting plant growth and yield. To understand the molecular mechanisms activated in response to salt in plants, we investigated the Catharanthus roseus Receptor like Kinase 1 Like (CrRLK1L) family, which contains well described sensors previously shown to be involved in maintaining and sensing the structural integrity of the cell walls. We found that herk1the1-4 double mutants, lacking the function of the Arabidopsis thaliana Receptor like Kinase HERKULES1 combined with a gain-of-function allele of THESEUS1, phenocopied the phenotypes previously reported in plants lacking FERONIA (FER) function. We report that both fer-4 and herk1the1-4 mutants respond strongly to salt application, resulting in a more intense activation of early and late stress responses. We also show that salt triggers de-methyl esterification of loosely bound pectins, responsible for the activation of several salt response signaling pathways. Addition of calcium chloride or chemically inhibiting pectin methyl esterase (PME) activity reduced activation of the early signaling protein Mitogen Activated Protein Kinase 6 (MPK6) as well as amplitude of salt-induced marker gene induction. MPK6 is required for the full induction of the salt-induced gene expression markers we tested. The sodium specific root halotropism response on the other hand, appears independent of MPK6 or calcium application, and is only mildly influenced by the cell wall sensors FER/HERK1/THE1-4 or alteration of PME activity. We hypothesize a model where salt-triggered modification of pectin requires the functionality of FER alone or the HERK1/THE1 combination to attenuate salt responses. Collectively, our results show the complexity of salt stress responses and salt sensing mechanisms and their connection to cell wall modifications, responsible for several salt response pathways and ultimately plant resilience to salinity.

plant biology↗