Casein kinase 2 α and β subunits inversely modulate ABA signal output in Arabidopsis protoplasts

Interaction of Soybean (Glycine max (L.) Merr.) Class II ACBPs with MPK2 and SAPK2 Kinases: New Insights into the Regulatory Mechanisms of Plant ACBPs

Plant acyl-CoA-binding proteins (ACBPs) function in plant development and stress responses, with some ACBPs interacting with protein partners. This study tested the interaction between two Class II GmACBPs (Glycine max ACBPs) and seven kinases, using yeast two-hybrid (Y2H) assays and bimolecular fluorescence complementation (BiFC). The results revealed that both GmACBP3.1 and GmACBP4.1 interact with two soybean kinases, a mitogen-activated protein kinase MPK2, and a serine/threonine-protein kinase SAPK2, highlighting the significance of the ankyrin-repeat (ANK) domain in facilitating protein-protein interactions. Moreover, an in vitro kinase assay and subsequent Phos-tag SDS-PAGE determined that GmMPK2 and GmSAPK2 possess the ability to phosphorylate Class II GmACBPs. Additionally, the kinase-specific phosphosites for Class II GmACBPs were predicted using databases. The HDOCK server was also utilized to predict the binding models of Class II GmACBPs with these two kinases, and the results indicated that the affected residues were located in the ANK region of Class II GmACBPs in both docking models, aligning with the findings of the Y2H and BiFC experiments. This is the first report describing the interaction between Class II GmACBPs and kinases, suggesting that Class II GmACBPs have potential as phospho-proteins that impact signaling pathways.

Casein kinase CK2 structure and activities in plants

Casein kinase CK2 is a highly conserved serine/threonine protein kinase and exists in all eukaryotes. It has been demonstrated to be widely involved in the biological processes of plants. The CK2 holoenzyme is a heterotetramer consisting of two catalytic subunits (α and/or α') and two regulatory subunits (β). CK2 in plants is generally encoded by multiple genes, with monomeric and oligomeric forms present in the tissue. Various subunit genes of CK2 have been cloned and characterized from Arabidopsis thaliana, tobacco, maize, wheat, tomato, and other plants. This paper reviews the structural features of CK2, provides a clear classification of its physiological functions and mechanisms of action, and elaborates on the regulation of CK2 activity to provide a knowledge base for subsequent studies of CK2 in plants.

The Molecular Mechanism of Yellow Mushroom (Floccularia luteovirens) Response to Strong Ultraviolet Radiation on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP) is the highest plateau in the world, and its ultraviolet (UV) radiation is much greater than that of other regions in the world. Yellow mushroom (Floccularia luteovirens) is a unique and widely distributed edible fungus on the QTP. However, the molecular mechanism of F. luteovirens’s response to strong UV radiation remains unclear. Herein, we reported the 205 environmental adaptation and information processing genes from genome of F. luteovirens. In addition, we assembled the RNA sequence of UV-affected F. luteovirens at different growth stages. The results showed that in response to strong UV radiation, a total of 11,871 significantly different genes were identified, of which 4,444 genes in the vegetative mycelium (VM) stage were significantly different from the young fruiting bodies (YFB) stage, and only 2,431 genes in the YFB stage were significantly different from fruiting bodies (FB) stage. A total of 225 differentially expressed genes (DEGs) were found to be involved in environmental signal transduction, biochemical reaction preparation and stress response pathway, pigment metabolism pathway, and growth cycle regulation, so as to sense UV radiation, promote repair damage, regulate intracellular homeostasis, and reduce oxidative damage of UV radiation. On the basis of these results, a molecular regulation model was proposed for the response of F. luteovirens to strong UV radiation. These results revealed the molecular mechanism of adaptation of F. luteovirens adapting to strong UV radiation, and provided novel insights into mechanisms of fungi adapting to extreme environmental conditions on the QTP; the production the riboflavin pigment of the endemic fungi (Yellow mushroom) in the QTP was one of the response to extreme environment of the strong UV radiation.

Small RNA Sequencing Revealed that miR4415, a Legume-Specific miRNA, was Involved in the Cold Acclimation of Ammopiptanthus nanus by Targeting an L-Ascorbate Oxidase Gene and Regulating the Redox State of Apoplast

MicroRNAs (miRNAs) are small endogenous single-stranded RNAs that regulate plant growth, development, and environmental stress response posttranscriptionally. Ammopiptanthus nanus, a rare evergreen broad-leaved shrub in the temperate area of Central Asia, can tolerate freezing stress as low as -30 degrees centigrade in winter, and miRNA might be involved in the cold acclimation which enables A. nanus to obtain tolerance to freezing stress. Systematic identification and functional analysis of the miRNAs involved in the cold acclimation in A. nanus may promote understanding of the miRNA-mediated gene regulation network underlying cold acclimation. Here, based on small RNA and degradome sequencing, 256 miRNAs and 1,808 miRNA-target pairs were identified in A. nanus. A total of 39 cold-responsive miRNAs were identified, of which 29 were upregulated and ten were downregulated. These cold-responsive miRNAs may participate in the cold acclimation by regulating redox homeostasis (miR398, miR4415, and miR408), calcium signaling (miR5225 and miR5211), growth and development (miR159 and miR390), and small RNA-mediated gene silencing (miR168 and miR1515). We found that miR4415, a legume-specific miRNA, is involved in the cold acclimation of A. nanus by targeting an L-ascorbate oxidase gene and then regulating the redox state of the apoplast. Our study provides important data for understanding the regulatory role of miRNA in the cold acclimation of A. nanus.

Cellular Phosphorylation Signaling and Gene Expression in Drought Stress Responses: ABA-Dependent and ABA-Independent Regulatory Systems

Drought is a severe and complex abiotic stress that negatively affects plant growth and crop yields. Numerous genes with various functions are induced in response to drought stress to acquire drought stress tolerance. The phytohormone abscisic acid (ABA) accumulates mainly in the leaves in response to drought stress and then activates subclass III SNF1-related protein kinases 2 (SnRK2s), which are key phosphoregulators of ABA signaling. ABA mediates a wide variety of gene expression processes through stress-responsive transcription factors, including ABA-RESPONSIVE ELEMENT BINDING PROTEINS (AREBs)/ABRE-BINDING FACTORS (ABFs) and several other transcription factors. Seed plants have another type of SnRK2s, ABA-unresponsive subclass I SnRK2s, that mediates the stability of gene expression through the mRNA decay pathway and plant growth under drought stress in an ABA-independent manner. Recent research has elucidated the upstream regulators of SnRK2s, RAF-like protein kinases, involved in early responses to drought stress. ABA-independent transcriptional regulatory systems and ABA-responsive regulation function in drought-responsive gene expression. DEHYDRATION RESPONSIVE ELEMENT (DRE) is an important cis-acting element in ABA-independent transcription, whereas ABA-RESPONSIVE ELEMENT (ABRE) cis-acting element functions in ABA-responsive transcription. In this review article, we summarize recent advances in research on cellular and molecular drought stress responses and focus on phosphorylation signaling and transcription networks in Arabidopsis and crops. We also highlight gene networks of transcriptional regulation through two major regulatory pathways, ABA-dependent and ABA-independent pathways, that ABA-responsive subclass III SnRK2s and ABA-unresponsive subclass I SnRK2s mediate, respectively. We also discuss crosstalk in these regulatory systems under drought stress.

The casein kinase 2 β subunit CK2B1 is required for swollen stem formation via cell cycle control in vegetable Brassica juncea

The swollen stem is a determinant of yield for the stem-type vegetable Brassica juncea that is representative of vegetative organ formation. However, the genetic mechanism underlying swollen stem formation and its regulation remains unknown. In this study, we identified a casein kinase 2 β subunit 1 (CK2B1) and revealed its role in swollen stem formation. Genotyping analysis revealed that a homozygous variation in the CK2B1 promoter is responsible for swollen stem formation, and the promoter activity of CK2B1 was significantly associated with the variations between swollen stem and non-swollen stem types. CK2B1 was exclusively located in the nucleus and expressed in the stem nodes of the plant. Swollen stem formation was blocked when CK2B1 expression was silenced, and induced in a backcross population carrying a swollen stem genotype, which indicates that CK2B1 is required for swollen stem formation. Cell numbers were increased during swollen stem formation and decreased in CK2B1-silenced expression plant, indicating that CK2B1 regulates swollen stem formation via cell division. CK2B1 directly interacted with E2Fa, a regulator of G1/S transition in the cell cycle, in which CK2 phosphorylates E2Fa. Our results revealed that CK2B1 affects swollen stem formation via the control of the cell cycle. These findings help to elucidate the signals that control swollen stem formation and provide a promising molecular target to enhance the yield of vegetative organ formation.

Precise Editing of the OsPYL9 Gene by RNA-Guided Cas9 Nuclease Confers Enhanced Drought Tolerance and Grain Yield in Rice (Oryza sativa L.) by Regulating Circadian Rhythm and Abiotic Stress Responsive Proteins

Abscisic acid (ABA) is involved in regulating drought tolerance, and pyrabactin resistance-like (PYL) proteins are known as ABA receptors. To elucidate the role of one of the ABA receptors in rice, OsPYL9 was mutagenized through CRISPR/Cas9 in rice. Homozygous and heterozygous mutant plants lacking any off-targets and T-DNA were screened based on site-specific sequencing and used for morpho-physiological, molecular, and proteomic analysis. Mutant lines appear to accumulate higher ABA, antioxidant activities, chlorophyll content, leaf cuticular wax, and survival rate, whereas a lower malondialdehyde level, stomatal conductance, transpiration rate, and vascular bundles occur under stress conditions. Proteomic analysis found a total of 324 differentially expressed proteins (DEPs), out of which 184 and 140 were up and downregulated, respectively. The OsPYL9 mutants showed an increase in grain yield under both drought and well watered field conditions. Most of the DEPs related to circadian clock rhythm, drought response, and reactive oxygen species were upregulated in the mutant plants. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEPs were only involved in circadian rhythm and Gene Ontology (GO) analysis showed that most of the DEPs were involved in response to abiotic stimulus, and abscisic acid-activated signaling pathways. Protein GIGANTEA, Adagio-like, and Pseudo-response regulator proteins showed higher interaction in protein–protein interaction (PPI) network. Thus, the overall results showed that CRISPR/Cas9-generated OsPYL9 mutants have potential to improve both drought tolerance and the yield of rice. Furthermore, global proteome analysis provides new potential biomarkers and understandings of the molecular mechanism of rice drought tolerance.

Chemical Manipulation of Abscisic Acid Signaling: A New Approach to Abiotic and Biotic Stress Management in Agriculture

The phytohormone abscisic acid (ABA) is the best-known stress signaling molecule in plants. ABA protects sessile land plants from biotic and abiotic stresses. The conserved pyrabactin resistance/pyrabactin resistance-like/regulatory component of ABA receptors (PYR/PYL/RCAR) perceives ABA and triggers a cascade of signaling events. A thorough knowledge of the sequential steps of ABA signaling will be necessary for the development of chemicals that control plant stress responses. The core components of the ABA signaling pathway have been identified with adequate characterization. The information available concerning ABA biosynthesis, transport, perception, and metabolism has enabled detailed functional studies on how the protective ability of ABA in plants might be modified to increase plant resistance to stress. Some of the significant contributions to chemical manipulation include ABA biosynthesis inhibitors, and ABA receptor agonists and antagonists. Chemical manipulation of key control points in ABA signaling is important for abiotic and biotic stress management in agriculture. However, a comprehensive review of the current knowledge of chemical manipulation of ABA signaling is lacking. Here, a thorough analysis of recent reports on small-molecule modulation of ABA signaling is provided. The challenges and prospects in the chemical manipulation of ABA signaling for the development of ABA-based agrochemicals are also discussed.

Arabidopsis CK2 family gene CKB3 involved in abscisic acid signaling

CKB3 is a regulatory (beta) subunit of CK2. In this study Arabidopsis thaliana homozygous T-DNA mutant ckb3 was studied to understand the role of CKB3 in abscisic acid (ABA) signaling. The results shown: CKB3 was expressed in all organs and the highest expression in the seeds, followed by the root. During seed germination and root growth the ckb3 mutant showed reduced sensitivity to ABA. The ckb3 mutant had more stomatal opening and increased proline accumulation and leaf water loss. The expression levels of number of genes in the ABA regulatory network had changed. This study demonstrates that CKB3 is an ABA signaling-related gene and may play a positive role in ABA signaling.

Protein kinase CK2α subunits constitutively activate ABA signaling in Arabidopsis

Protein kinase CK2 (formerly known as casein kinase II), a Ser/Thr protein kinase highly conserved in eukaryotes, is essential for cell survival by regulating a wide range of plant growth, development, and stress responses. A growing body of evidence has shown a link between CK2 and abscisic acid (ABA) signaling in response to abiotic stress. However, the roles of CK2 subunits in ABA signaling remain unclear in plants. Our recent work in Arabidopsis thaliana has revealed that CK2α and CK2β subunits inversely modulate ABA signal output. Here, we examine the roles of CK2αs, by assessing how CK2αs affect ABA signaling. Together with the previous findings, our mutant and transient expression analyses demonstrate that CK2αs positively modulate ABA signaling through the core ABA signaling pathway in the presence of ABA, though the positive effect of CK2αs are much smaller than that of core ABA signaling components in ABA response. In addtion, our current and previous findings also suggest that CK2αs play a role in maintaining constitutively active ABA signaling even in the absence of ABA independently of the core ABA signaling pathway. Thus, we found that CK2αs constitutively activate ABA signaling in the presence or absence of ABA in a different manner in Arabidopsis plants.