Identification, Expression, and Interaction Network Analyses of the CDPK Gene Family Reveal Their Involvement in the Development, Ripening, and Abiotic Stress Response in Banana

Genome-wide identification of the CPK gene family in wheat (Triticum aestivum L.) and characterization of TaCPK40 associated with seed dormancy and germination

Calcium-dependent protein kinases (CPKs), important sensors of calcium signals, play an essential role in plant growth, development, and stress responses. Although the CPK gene family has been characterized in many plants, the functions of the CPK gene family in wheat, including their relationship to seed dormancy and germination, remain unclear. In this study, we identified 84 TaCPK genes in wheat (TaCPK1-84). According to their phylogenetic relationship, they were divided into four groups (I-IV). TaCPK genes in the same group were found to have similar gene structures and motifs. Chromosomal localization indicated that TaCPK genes were unevenly distributed across 21 wheat chromosomes. TaCPK gene expansion occurred through segmental duplication events and underwent strong negative selection. A large number of cis-regulatory elements related to light response, phytohormone response, and abiotic stress response were identified in the upstream promoter sequences of TaCPK genes. TaCPK gene expression was found to be tissue- and growth-stage-diverse. Analysis of the expression patterns of several wheat varieties with contrasting seed dormancy and germination phenotypes resulted in the identification of 11 candidate genes (TaCPK38/-40/-43/-47/-50/-60/-67/-70/-75/-78/-80) which are likely associated with seed dormancy and germination. The ectopic expression of TaCPK40 in Arabidopsis promoted seed germination and reduced abscisic acid (ABA) sensitivity during germination, indicating that TaCPK40 negatively regulates seed dormancy and positively regulates seed germination. These findings advance our understanding of the multifaceted functions of CPK genes in seed dormancy and germination, and provide potential candidate genes for controlling wheat seed dormancy and germination.

Cell Wall Integrity Signaling in Fruit Ripening

Plant cell walls are essential structures for plant growth and development as well as plant adaptation to environmental stresses. Thus, plants have evolved signaling mechanisms to monitor the changes in the cell wall structure, triggering compensatory changes to sustain cell wall integrity (CWI). CWI signaling can be initiated in response to environmental and developmental signals. However, while environmental stress-associated CWI signaling has been extensively studied and reviewed, less attention has been paid to CWI signaling in relation to plant growth and development under normal conditions. Fleshy fruit development and ripening is a unique process in which dramatic alternations occur in cell wall architecture. Emerging evidence suggests that CWI signaling plays a pivotal role in fruit ripening. In this review, we summarize and discuss the CWI signaling in relation to fruit ripening, which will include cell wall fragment signaling, calcium signaling, and NO signaling, as well as Receptor-Like Protein Kinase (RLKs) signaling with an emphasis on the signaling of FERONIA and THESEUS, two members of RLKs that may act as potential CWI sensors in the modulation of hormonal signal origination and transduction in fruit development and ripening.

Identification of CDPKs involved in TaNOX7 mediated ROS production in wheat

As the critical sensors and decoders of calcium signal, calcium-dependent protein kinase (CDPK) has become the focus of current research, especially in plants. However, few resources are available on the properties and functions of CDPK gene family in Triticum aestivum (TaCDPK). Here, a total of 79 CDPK genes were identified in the wheat genome. These TaCDPKs could be classified into four subgroups on phylogenesis, while they may be classified into two subgroups based on their tissue and organ-spatiotemporal expression profiles or three subgroups according to their induced expression patterns. The analysis on the signal network relationships and interactions of TaCDPKs and NADPH (reduced nicotinamide adenine dinucleotide phosphate oxidases, NOXs), the key producers for reactive oxygen species (ROS), showed that there are complicated cross-talks between these two family proteins. Further experiments demonstrate that, two members of TaCDPKs, TaCDPK2/4, can interact with TaNOX7, an important member of wheat NOXs, and enhanced the TaNOX7-mediated ROS production. All the results suggest that TaCDPKs are highly expressed in wheat with distinct tissue or organ-specificity and stress-inducible diversity, and play vital roles in plant development and response to biotic and abiotic stresses by directly interacting with TaNOXs for ROS production.

The Role of Calmodulin Binding Transcription Activator in Plants under Different Stressors: Physiological, Biochemical, Molecular Mechanisms of Camellia sinensis and Its Current Progress of CAMTAs

Low temperatures have a negative effect on plant development. Plants that are exposed to cold temperatures undergo a cascade of physiological, biochemical, and molecular changes that activate several genes, transcription factors, and regulatory pathways. In this review, the physiological, biochemical, and molecular mechanisms of Camellia sinensis have been discussed. Calmodulin binding transcription activator (CAMTAs) by molecular means including transcription is one of the novel genes for plants' adaptation to different abiotic stresses, including low temperatures. Therefore, the role of CAMTAs in different plants has been discussed. The number of CAMTAs genes discussed here are playing a significant role in plants' adaptation to abiotic stress. The illustrated diagrams representing the mode of action of calcium (Ca²⁺) with CAMTAs have also been discussed. In short, Ca²⁺ channels or Ca²⁺ pumps trigger and induce the Ca²⁺ signatures in plant cells during abiotic stressors, including low temperatures. Ca²⁺ signatures act with CAMTAs in plant cells and are ultimately decoded by Ca²⁺sensors. To the best of our knowledge, this is the first review reporting CAMAT's current progress and potential role in C. sinensis, and this study opens a new road for researchers adapting tea plants to abiotic stress.

A calcium-dependent protein kinase gene SpCPK33 from Solanum pennellii associated with increased cold tolerance in tomato

Calcium-dependent protein kinases (CDPKs, CPKs) represent a vital class of calcium sensors, which play a crucial role in plant growth, development and adaption to complex environmental stresses. Wild species tend to exhibit greater tolerance than cultivated species under environmental stress. Here, we isolated a calcium-dependent protein kinase gene SpCPK33 located primarily on the plasma membrane of abiotic-resistant species (Solanum pennellii LA0716). It was highly expressed in stems and leaves and was also induced by cold stress. Compared with WT plants, the overexpression of SpCPK33 in cultivated tomato (cv M82) enhanced its tolerance to cold stress. Transgenic lines demonstrated strong vitality under low temperature treatment. Moreover, the levels of malondialdehyde (MDA) and reactive oxygen species (ROS) were decreased in SpCPK33-overexpressing plants. The activities of antioxidant enzymes and the levels of osmotic regulatory substances were higher. The transcript levels of cold stress-related genes were up-regulated. In summary, the results indicate that SpCPK33-overexpressing transgenic plants experience less severe chilling injury under cold stress, and improved tomato cold tolerance by scavenging ROS accumulation and modulating the expression of stress-related genes.

GhCDPK60 positively regulates drought stress tolerance in both transgenic Arabidopsis and cotton by regulating proline content and ROS level

Calcium-Dependent Protein Kinases (CDPKs) involved in regulating downstream components of calcium signaling pathways play a role in tolerance to abiotic stresses and seed development in plants. However, functions of only a few cotton CDPKs have been clarified at present. In this study, 80 conserved CDPKs in Gossypium hirsutum L. were identified and characterized, which was divided into four subgroups. Among them, the transcript level of GhCDPK60 was significantly upregulated under drought and several hormone treatments. And we found that the expression levels of several stress-inducible genes down-regulated in GhCDPK60-silence cotton and up-regulated in GhCDPK60-overexpressing Arabidopsis. In addition, physiological analyses demonstrated that GhCDPK60 improved drought stress tolerance by improving the osmotic adjustment ability and reducing the accumulation of reactive oxygen species (ROS) in plants. These findings broaden our understanding of the biological roles of GhCDPK60 and mechanisms underlying drought stress tolerance in cotton.

Combined physiological and transcriptome analysis revealed the response mechanism of Pogostemon cablin roots to p-hydroxybenzoic acid

Pogostemon cablin (patchouli) cultivation is challenged by serious soil sickness, of which autotoxins accumulation is a major cause. p-hydroxybenzoic acid (p-HBA) is one of the main autotoxins of patchouli. However, the molecular mechanism underlying the response of patchouli to p-HBA remains unclear. In this study, RNA-sequencing combined with physiological analysis was used to monitor the dynamic transcriptomic and physiological changes in patchouli seedlings 0, 6, 12, 24, 48, and 96 h after p-HBA treatment. p-HBA stress inhibited root biomass accumulation, induced excessive hydrogen peroxide accumulation and lipid peroxidation, and activated most antioxidant enzymes. Compared with that of the control, the osmotic adjustment substance content was elevated with treatment. Subsequently, 15,532, 8,217, 8,946, 2,489, and 5,843 differentially expressed genes (DEGs) at 6, 12, 24, 48, and 96 h after p-HBA treatment, respectively, were identified in patchouli roots. GO functional enrichment analysis showed that the DEGs were enriched mainly in plasma membrane, defense response, response to chitin, DNA-binding transcription factor activity and abscisic acid-activated signaling pathway. The upregulated genes were involved in glycolysis/gluconeogenesis, cysteine and methionine metabolism, starch and sucrose metabolism, biosynthesis of unsaturated fatty acids, and linoleic acid metabolism. Genes associated with MAPK signaling pathway-plant, plant-pathogen interaction, plant hormone signal transduction were downregulated with p-HBA treatment. These pathways are related to root browning and rotting, leading to plant death.

The Developmental Delay of Seedlings With Cotyledons Only Confers Stress Tolerance to Suaeda aralocaspica (Chenopodiaceae) by Unique Performance on Morphology, Physiology, and Gene Expression

Cotyledons play an important role in seedling establishment, although they may just exist for a short time and become senescent upon the emergence of euphylla. So far, the detailed function of cotyledons has not been well understood. Suaeda aralocaspica is an annual halophyte distributed in cold deserts; its cotyledons could exist for a longer time, even last until maturity, and they must exert a unique function in seedling development. Therefore, in this study, we conducted a series of experiments to investigate the morphological and physiological performances of cotyledons under salt stress at different developmental stages. The results showed that the cotyledons kept growing slowly to maintain the normal physiological activities of seedlings by balancing phytohormone levels, accumulating osmoprotectants and antioxidants, and scavenging reactive oxygen species (ROS). Salt stress activated the expression of osmoprotectant-related genes and enhanced the accumulation of related primary metabolites. Furthermore, differentially expressed transcriptional profiles of the cotyledons were also analyzed by cDNA-AFLP to gain an understanding of cotyledons in response to development and salt stress, and the results revealed a progressive increase in the expression level of development-related genes, which accounted for a majority of the total tested TDFs. Meanwhile, key photosynthetic and important salt stress-related genes also actively responded. All these performances suggest that "big cotyledons" are experiencing a delayed but active developmental process, by which S. aralocaspica may survive the harsh condition of the seedling stage.

In vitro drought stress and drought-related gene expression in banana

BACKGROUND

Banana is largely grown in tropical and subtropical climates. It is rich in various food components and has quite a high economic value. Unavailable ecological and agricultural conditions cause quantitative and qualitative losses in banana cultivation. Along with global climate change, drought stress is becoming prominent day by day.

METHODS AND RESULTS

Micropropagation and rooting performance of Azman and Grand Naine banana cultivars were investigated under in vitro drought stress conditions. The expression levels of four different genes of CDPK gene family in leaf and root tissues of the rooted plants were determined with the use of qRT-PCR. Greater expression levels of four MaCDPK genes were seen in Azman cultivar than in Grand Naine cultivar. MaCDPK9 and MaCDPK21 had greater expression levels in root tissue and MaCDPK1 and MaCDPK40 genes in leaf tissues.

CONCLUSIONS

Response of different banana cultivars to in vitro drought stress was determined in this study. The expression levels of the genes of CDPK gene family with a significant role in drought stress had significant contributions in elucidation of banana plant response to drought stress.

Calcium Mediated Cold Acclimation in Plants: Underlying Signaling and Molecular Mechanisms

Exposure of plants to low temperatures adversely affects plant growth, development, and productivity. Plant response to cold stress is an intricate process that involves the orchestration of various physiological, signaling, biochemical, and molecular pathways. Calcium (Ca²⁺) signaling plays a crucial role in the acquisition of several stress responses, including cold. Upon perception of cold stress, Ca²⁺ channels and/or Ca²⁺ pumps are activated, which induces the Ca²⁺ signatures in plant cells. The Ca²⁺ signatures spatially and temporally act inside a plant cell and are eventually decoded by specific Ca²⁺ sensors. This series of events results in the molecular regulation of several transcription factors (TFs), leading to downstream gene expression and withdrawal of an appropriate response by the plant. In this context, calmodulin binding transcription activators (CAMTAs) constitute a group of TFs that regulate plant cold stress responses in a Ca²⁺ dependent manner. The present review provides a catalog of the recent progress made in comprehending the Ca²⁺ mediated cold acclimation in plants.

The Potential of Molecular Indicators of Plant Virus Infection: Are Plants Able to Tell Us They Are Infected?

To our knowledge, there are no reports that demonstrate the use of host molecular markers for the purpose of detecting generic plant virus infection. Two approaches involving molecular indicators of virus infection in the model plant Arabidopsis thaliana were examined: the accumulation of small RNAs (sRNAs) using a microfluidics-based method (Bioanalyzer); and the transcript accumulation of virus-response related host plant genes, suppressor of gene silencing 3 (AtSGS3) and calcium-dependent protein kinase 3 (AtCPK3) by reverse transcriptase-quantitative PCR (RT-qPCR). The microfluidics approach using sRNA chips has previously demonstrated good linearity and good reproducibility, both within and between chips. Good limits of detection have been demonstrated from two-fold 10-point serial dilution regression to 0.1 ng of RNA. The ratio of small RNA (sRNA) to ribosomal RNA (rRNA), as a proportion of averaged mock-inoculation, correlated with known virus infection to a high degree of certainty. AtSGS3 transcript decreased between 14- and 28-days post inoculation (dpi) for all viruses investigated, while AtCPK3 transcript increased between 14 and 28 dpi for all viruses. A combination of these two molecular approaches may be useful for assessment of virus-infection of samples without the need for diagnosis of specific virus infection.

Interactions between calcium and ABA signaling pathways in the regulation of fruit ripening

Fruit ripening and senescence are finely controlled by plant hormones such as ethylene and abscisic acid (ABA) but also by calcium ions and by calcium-dependent signaling pathways. Although there are extensive data supporting an interaction between ethylene and calcium in fruit ripening, the regulatory mechanisms resulting from the interaction between ABA and calcium have not yet been fully clarified. In this article, we have reviewed the full roles of calcium and its sensors (CaM, CMLs, CDPKs, CBLs) as well as ABA and the interactions between the two signaling pathways in the regulation of stress responses and in fruit ripening. To illustrate the possible interaction between calcium sensors and ABA signaling components in the control of fruit ripening, we propose an interaction model between the calcium and ABA signaling pathways.

Evolution and expression analysis of CDPK genes under drought stress in two varieties of potato

OBJECTIVES

Calcium-dependent protein kinases (CDPKs) function directly in plant development and stress responses. We used whole genome sequences and mRNA expression data to analyze the phylogenetic relationships, gene structure, collinearity, and differential expression of CDPKs in two differentially drought-tolerant potato varieties.

RESULTS

In total, we identified 25 CDPK proteins belonging to four subfamilies. There was a significant collinear relationship among 13 CDPK genes belonging to four segmentally duplicated pairs. Subcellular prediction implied that all StCDPKs were localized at the plasma membrane. Analysis of promoter regions revealed that StCDPKs were photosensitive and responsive to biotic stress, abiotic stress, and hormone stimuli. RNA-seq analysis showed differential expression of StCDPKs among various potato tissues, and qPCR analysis revealed that 20 StCDPKs exhibited differential expression patterns under drought stress between drought-tolerant (QS9) and drought sensitive (Atl) potato varieties. Among these, the most strongly drought-induced genes were respectively StCDPK3 and StCDPK23, highlighting these as attractive candidate genes for further functional analyses of drought-stress responses in potato.

CONCLUSIONS

Our results demonstrating the tissue specific and drought stress-responsive StCDPK genes of potato both provide a reference for further research about the functions of CDPK family proteins and should support ongoing efforts for the further genetic improvement of potato.

Investigation of the Nature of CgCDPK and CgbHLH001 Interaction and the Function of bHLH Transcription Factor in Stress Tolerance in Chenopodium glaucum

Calcium-dependent protein kinase (CDPK) and its substrates play important roles in plant response to stress. So far, the documentation on the characterization of the CDPK and downstream interaction components (especially transcription factors, TFs) is limited. In the present study, an interaction between CgCDPK (protein kinase) (accession no. MW26306) and CgbHLH001 (TF) (accession no. MT797813) from a halophyte Chenopodium glaucum was further dissected. Firstly, we revealed that the probable nature between the CgCDPK and CgbHLH001 interaction was the phosphorylation, and the N-terminus of CgbHLH001, especially the 96th serine (the potential phosphorylation site) within it, was essential for the interaction, whereas the mutation of ⁹⁶Ser to alanine did not change its nuclear localization, which was determined by the N-terminus and bHLH domain together. Furthermore, we verified the function of CgbHLH001 gene in response to stress by ectopic overexpression in tobacco; the transgenic lines presented enhanced stress tolerance probably by improving physiological performance and stress-related gene expression. In conclusion, we characterized the biological significance of the interaction between CDPK and bHLH in C. glaucum and verified the positive function of CgbHLH001 in stress tolerance, which may supply more evidence in better understanding of the CDPK signaling pathway in response to adversity.

Insights on Calcium-Dependent Protein Kinases (CPKs) Signaling for Abiotic Stress Tolerance in Plants

Abiotic stresses are the major limiting factors influencing the growth and productivity of plants species. To combat these stresses, plants can modify numerous physiological, biochemical, and molecular processes through cellular and subcellular signaling pathways. Calcium-dependent protein kinases (CDPKs or CPKs) are the unique and key calcium-binding proteins, which act as a sensor for the increase and decrease in the calcium (Ca) concentrations. These Ca flux signals are decrypted and interpreted into the phosphorylation events, which are crucial for signal transduction processes. Several functional and expression studies of different CPKs and their encoding genes validated their versatile role for abiotic stress tolerance in plants. CPKs are indispensable for modulating abiotic stress tolerance through activation and regulation of several genes, transcription factors, enzymes, and ion channels. CPKs have been involved in supporting plant adaptation under drought, salinity, and heat and cold stress environments. Diverse functions of plant CPKs have been reported against various abiotic stresses in numerous research studies. In this review, we have described the evaluated functions of plant CPKs against various abiotic stresses and their role in stress response signaling pathways.