The Effect of Stress Hormones, Ultraviolet C, and Stilbene Precursors on Expression of Calcineurin B-like Protein (CBL) and CBL-Interacting Protein Kinase (CIPK) Genes in Cell Cultures and Leaves of Vitis amurensis Rupr

Calcium serves as a crucial messenger in plant stress adaptation and developmental processes. Plants encode several multigene families of calcium sensor proteins with diverse functions in plant growth and stress responses. Several studies indicated that some calcium sensors may be involved in the regulation of secondary metabolite production in plant cells. The present study aimed to investigate expression of calcineurin B-like proteins (CBL) and CBL-interacting protein kinase (CIPK) in response to conditions inducting biosynthesis of stilbenes in grapevine. We investigated CBL and CIPK gene expression in wild-growing grapevine Vitis amurensis Rupr., known as a rich stilbene source, in response to the application of stilbene biosynthesis-inducing conditions, including application of stress hormones (salicylic acid or SA, methyl jasmonate or MeJA), phenolic precursors (p-coumaric acids or CA), and ultraviolet irradiation (UV-C). The influence of these effectors on the levels of 13 VaCBL and 27 VaCIPK mRNA transcripts as well as on stilbene production was analyzed by quantitative real-time RT-PCR in the leaves and cell cultures of V. amurensis. The data revealed that VaCBL4-1 expression considerably increased after UV-C treatment in both grapevine cell cultures and leaves. The expression of VaCIPK31, 41-1, and 41-2 also increased, but this increase was mostly detected in cell cultures of V. amurensis. At the same time, expression of most VaCBL and VaCIPK genes was markedly down-regulated both in leaves and cell cultures of V. amurensis, which may indicate that the CBLs and CIPKs are involved in negative regulation of stilbene accumulation (VaCBL8, 10a-2, 10a-4, 11, 12, VaCIPK3, 9-1, 9-2, 12, 21-1, 21-2, 33, 34, 35, 36, 37, 39, 40, 41-3, 41-4). The results obtained provide new information of CBL and CIPK implication in the regulation of plant secondary metabolism in response to stress hormones, metabolite precursors, and UV-C irradiation.

Calcium decoders and their targets: The holy alliance that regulate cellular responses in stress signaling

Calcium (Ca²⁺) signaling is versatile communication network in the cell. Stimuli perceived by cells are transposed through Ca²⁺-signature, and are decoded by plethora of Ca²⁺ sensors present in the cell. Calmodulin, calmodulin-like proteins, Ca²⁺-dependent protein kinases and calcineurin B-like proteins are major classes of proteins that decode the Ca²⁺ signature and serve in the propagation of signals to different parts of cells by targeting downstream proteins. These decoders and their targets work together to elicit responses against diverse stress stimuli. Over a period of time, significant attempts have been made to characterize as well as summarize elements of this signaling machinery. We begin with a structural overview and amalgamate the newly identified Ca²⁺ sensor protein in plants. Their ability to bind Ca²⁺, undergo conformational changes, and how it facilitates binding to a wide variety of targets is further embedded. Subsequently, we summarize the recent progress made on the functional characterization of Ca²⁺ sensing machinery and in particular their target proteins in stress signaling. We have focused on the physiological role of Ca²⁺, the Ca²⁺ sensing machinery, and the mode of regulation on their target proteins during plant stress adaptation. Additionally, we also discuss the role of these decoders and their mode of regulation on the target proteins during abiotic, hormone signaling and biotic stress responses in plants. Finally, here, we have enumerated the limitations and challenges in the Ca²⁺ signaling. This article will greatly enable in understanding the current picture of plant response and adaptation during diverse stimuli through the lens of Ca²⁺ signaling.

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.

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 Bark of the Spruce Picea jezoensis Is a Rich Source of Stilbenes

Stilbenes are plant phenolic secondary metabolites that show beneficial effects on human health and possess high antifungal activity against plant pathogens. Currently, a search for plant sources with high stilbene levels is relevant, since stilbene content in various plant species can vary substantially and is often at a low level. In this paper, the bark and wood of Picea jezoensis were analyzed for the content and composition of stilbenes and compared with other known stilbene sources. The HPLC-MS analysis of P. jezoensis bark and wood extracted with different solvents and at different temperatures revealed the presence of 11 and 5 stilbenes, respectively. The highest number of stilbenes of 171 and 229 mg per g of the dry weight (mg/g DW) was extracted from the bark of P. jezoensis using methanol or ethanol at 60 °C for 2 h. Trans-astringin, trans-piceid, and trans-isorhapontin prevailed over other stilbenoids (99% of all detected stilbenes). The most abundant stilbene was trans-isorhapontin, reaching 217 mg/g DW or 87% of all stilbenes. An increase in the extraction time from 2 to 6 h did not considerably increase the detected level of stilbenes, while lower extraction temperatures (20 and 40 °C) significantly lowered stilbene yield. The content of stilbenes in the P. jezoensis bark considerably exceeded stilbene levels in other stilbene-producing plant species. The present data revealed that the bark of P. jezoensis is a rich source of stilbenes (primarily trans-isorhapontin) and provided effective stilbene extraction procedures.

Physiological Conditions and dsRNA Application Approaches for Exogenously induced RNA Interference in Arabidopsis thaliana

Recent studies have revealed that foliar application of double-stranded RNAs (dsRNAs) or small-interfering RNAs (siRNAs) encoding specific genes of plant pathogens triggered RNA interference (RNAi)-mediated silencing of the gene targets. However, a limited number of reports documented silencing of plant endogenes or transgenes after direct foliar RNA application. This study analyzed the importance of physiological conditions (plant age, time of day, soil moisture, high salinity, heat, and cold stresses) and different dsRNA application means (brush spreading, spraying, infiltration, inoculation, needle injection, and pipetting) for suppression of neomycin phosphotransferase II (NPTII) transgene in Arabidopsis thaliana, as transgenes are more prone to silencing. We observed a higher NPTII suppression when dsRNA was applied at late day period, being most efficient at night, which revealed a diurnal variation in dsRNA treatment efficacy. Exogenous NPTII-dsRNA considerably reduced NPTII expression in 4-week-old plants and only limited it in 2- and 6-week-old plants. In addition, a more discernible NPTII downregulation was detected under low soil moisture conditions. Treatment of adaxial and abaxial leaf surfaces by brushes, spraying, and pipetting showed a higher NPTII suppression, while infiltration and inoculation were less efficient. Thus, appropriate plant age, late time of day, low soil moisture, and optimal dsRNA application modes are important for exogenously induced gene silencing.

The Grapevine Calmodulin-Like Protein Gene CML21 Is Regulated by Alternative Splicing and Involved in Abiotic Stress Response

Calmodulin-like proteins (CMLs) represent a large family of plant calcium sensor proteins involved in the regulation of plant responses to environmental cues and developmental processes. In the present work, we identified four alternatively spliced mRNA forms of the grapevine CML21 gene that encoded proteins with distinct N-terminal regions. We studied the transcript abundance of CML21v1, CML21v2, CML21v3, and CML21v4 in wild-growing grapevine Vitis amurensis Rupr. in response to desiccation, heat, cold, high salinity, and high mannitol stress using quantitative real-time RT-PCR. The levels of all four splice variants of VaCML21 were highly induced in response to cold stress. In addition, VaCML21v1 and VaCML21v2 forms were highly modulated by all other abiotic stress treatments. Constitutive expression of VaCML21v2 and VaCML21v4 improved biomass accumulation of V. amurensis callus cell cultures under prolonged low temperature stress. Heterologous expression of the grapevine CML21v2 and VaCML21v4 splice variants in Arabidopsis improved survival rates of the transgenic plants after freezing. The VaCML21v2 overexpression enhanced activation of the cold stress-responsive marker genes AtDREB1A and AtDREB2A, while VaCML21v4 overexpression—AtCOR47, AtRD29A, AtRD29B, and AtKIN1 genes after freezing stress in the transgenic Arabidopsis. The results indicate that the grapevine CML21 gene acts as a positive regulator in the plant response to cold stress. The detected variety of CML21 transcripts and their distinct transcriptional responses suggested that this expansion of mRNA variants could contribute to the diversity of grapevine adaptive reactions.

Prescience of endogenous regulation in Arabidopsis thaliana by Pseudomonas putida MTCC 5279 under phosphate starved salinity stress condition

Phosphorus (P) availability and salinity stress are two major constraints for agriculture productivity. A combination of salinity and P starvation is known to be more deleterious to plant health. Plant growth promoting rhizobacteria are known to ameliorate abiotic stress in plants by increasing the availability of different nutrients. However, interaction mechanisms of plant grown under salinity and P stress condition and effect of beneficial microbe for stress alleviation is still obscure. Earlier we reported the molecular insight of auxin producing, phosphate solubilising Pseudomonas putida MTCC 5279 (RAR) mediated plant growth promotion in Arabidopsis thaliana. In present study new trait of proline and phosphatase production of RAR and its impact on modulation of physiological phenomenon under phosphate starved-salinity stress condition in A. thaliana has been investigated. Different physiological and molecular determinants under RAR- A. thaliana interaction showed that auxin producing RAR shows tryptophan dependence for growth and proline production in ATP dependant manner under salinity stress. However, under P deprived conditions growth and proline production are independent of tryptophan. RAR mediated lateral root branching and root hair density through modulation of abscisic acid signalling was observed. Acidic phosphatase activity under P starved and salinity stress condition was majorly modulated along with ROS metabolism and expression of stress responsive/phosphate transporter genes. A strong correlation of different morpho-physiological factor with RAR + salt conditions, showed We concluded that enhanced adverse effect of salinity with unavailability of P was dampened in presence of P. putida MTCC 5279 (RAR) in A. thaliana, though more efficiently salinity stress conditions. Therefore, alleviation of combined stress of salinity induced phosphate nutrient deficiency by inoculation of beneficial microbe, P. putida MTCC 5279 offer good opportunities for enhancing the agricultural productivity.

The Effect of Abiotic Stress Conditions on Expression of Calmodulin (CaM) and Calmodulin-Like (CML) Genes in Wild-Growing Grapevine Vitis amurensis

Plant calmodulins (CaMs) and calmodulin-like proteins (CMLs) are important plant Ca²⁺-binding proteins that sense and decode changes in the intracellular Ca²⁺ concentration arising in response to environmental stimuli. Protein Ca²⁺ sensors are presented by complex gene families in plants and perform diverse biological functions. In this study, we cloned, sequenced, and characterized three CaM and 54 CML mRNA transcripts of Vitis amurensis Rupr., a wild-growing grapevine with a remarkable stress tolerance. Using real-time quantitative RT-PCR, we analyzed transcript abundance of the identified VaCaMs and VaCMLs in response to water deficit, high salinity, high mannitol, cold and heat stresses. Expression of VaCaMs and 32 VaCMLs actively responded to the abiotic stresses and exhibited both positive and negative regulation patterns. Other VaCML members showed slight transcriptional regulation, remained essentially unresponsive or responded only after one time interval of the treatments. The substantial alterations in the VaCaM and VaCML transcript levels revealed their involvement in the adaptation of wild-growing grapevine to environmental stresses.

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.