Biology subjects

Shkolnik, D.

Publications and source records attributed to Shkolnik, D..

3 recordsLinked to original sources

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↗

bioRxiv2026

RBOHC-Generated ROS Tune GNOM-Dependent Root Halotropism in Arabidopsis

Halotropism--the directional growth of roots away from saline environments--requires coordinated integration of tropic cues. We show that halotropic bending in Arabidopsis thaliana roots is fine-tuned by a spatially confined, symmetric reactive oxygen species (ROS) domain generated by the NADPH oxidase RBOHC in elongation-zone epidermal cells. This domain, visualized by dihydrorhodamine-123 staining and confocal microscopy, emerges during the first hours of halostimulation and limits excessive curvature. Reducing ROS, either chemically with ascorbate or diphenyleneiodonium, or genetically in rbohC mutants, enhances halotropic bending, whereas miz2, defective in the ARF-GEF GNOM, exhibits negative halotropism due to an expanded and mislocalized ROS domain that disrupts spatial restriction. The miz2 rbohC double mutant shows a much weaker halotropic response than rbohC alone and similarly lacks the halotropic ROS signals in the elongation zone, indicating that GNOM acts upstream of RBOHC-mediated ROS production. Comparisons with hydrotropism--a moisture-seeking response also involving defined ROS distribution--suggest that GNOM-dependent regulation of RBOHC constitutes a shared module for adjusting root orientation to environmental gradients. Understanding these molecular mechanisms is essential for enhancing crop resilience to soil salinity, particularly in the context of increasing soil salinization driven by climate change.

plant biology↗

bioRxiv2023

Calcium regulation of the Arabidopsis Na+/K+ transporter HKT1;1 improves seed germination under salt stress

Calcium is known to improve seed-germination rates under salt stress. We investigated the involvement of calcium ions (Ca2+) in regulating HIGH-AFFINITY K+ TRANSPORTER 1 (HKT1;1), which encodes a Na+/K+ transporter, and its post-translational regulator TYPE 2C PROTEIN PHOSPHATASE 49 (PP2C49), in germinating Arabidopsis thaliana seedlings. Germination rates of hkt1 mutant seeds under salt stress remained unchanged by CaCl2 treatment in wild-type Arabidopsis, whereas pp2c49 mutant seeds displayed improved salt-stress tolerance in the absence of CaCl2 supplementation. Analysis of HKT1;1 and PP2C49 promoter activity revealed that CaCl2 treatment results in radicle-focused expression of HKT1;1 and reduction of the native radicle-exclusive expression of PP2C49. Ion-content analysis indicated that CaCl2 treatment improves K+ retention in germinating wild-type seedlings under salt stress, but not in hkt1 seedlings. Transgenic seedlings designed to exclusively express HKT1;1 in the radicle during germination displayed higher germination rates under salt stress than the wild type in the absence of CaCl2 treatment. Transcriptome analysis of germinating seedlings treated with CaCl2, NaCl, or both revealed 118 upregulated and 94 downregulated genes as responsive to the combined treatment. Bioinformatics analysis of the upstream sequences of CaCl2-NaCl-treatment-responsive upregulated genes revealed the abscisic acid response element CACGTGTC, a potential CaM-binding transcription activator-binding motif, as most prominent. Our findings suggest a key role for Ca2+ in mediating salt-stress responses during germination by regulating genes that function to maintain Na+ and K+ homeostasis, which is vital for seed germination under salt stress.

plant biology↗