CML24, regulated in expression by diverse stimuli, encodes a potential Ca2+ sensor that functions in responses to abscisic acid, daylength, and ion stress

Modulation of early gene expression responses to water deprivation stress by the E3 ubiquitin ligase ATL80: implications for retrograde signaling interplay

BACKGROUND

Primary response genes play a pivotal role in translating short-lived stress signals into sustained adaptive responses. In this study, we investigated the involvement of ATL80, an E3 ubiquitin ligase, in the dynamics of gene expression following water deprivation stress. We observed that ATL80 is rapidly activated within minutes of water deprivation stress perception, reaching peak expression around 60 min before gradually declining. ATL80, despite its post-translational regulation role, emerged as a key player in modulating early gene expression responses to water deprivation stress.

RESULTS

The impact of ATL80 on gene expression was assessed using a time-course microarray analysis (0, 15, 30, 60, and 120 min), revealing a burst of differentially expressed genes, many of which were associated with various stress responses. In addition, the diversity of early modulation of gene expression in response to water deprivation stress was significantly abolished in the atl80 mutant compared to wild-type plants. A subset of 73 genes that exhibited a similar expression pattern to ATL80 was identified. Among them, several are linked to stress responses, including ERF/AP2 and WRKY transcription factors, calcium signaling genes, MAP kinases, and signaling peptides. Promoter analysis predicts enrichment of binding sites for CAMTA1 and CAMTA5, which are known regulators of rapid stress responses. Furthermore, we have identified a group of differentially expressed ERF/AP2 transcription factors, proteins associated with folding and refolding, as well as pinpointed core module genes which are known to play roles in retrograde signaling pathways that cross-referenced with the early ATL80 transcriptome.

CONCLUSIONS

Based on these findings, we propose that ATL80 may target one or more components within the retrograde signaling pathways for degradation. In essence, ATL80 serves as a bridge connecting these signaling pathways and effectively functions as an alarm signal.

The calcium connection: exploring the intricacies of calcium signaling in plant-microbe interactions

The process of plant immune response is orchestrated by intracellular signaling molecules. Since plants are devoid of a humoral system, they develop extensive mechanism of pathogen recognition, signal perception, and intricate cell signaling for their protection from biotic and abiotic stresses. The pathogenic attack induces calcium ion accumulation in the plant cells, resulting in calcium signatures that regulate the synthesis of proteins of defense system. These calcium signatures induct different calcium dependent proteins such as calmodulins (CaMs), calcineurin B-like proteins (CBLs), calcium-dependent protein kinases (CDPKs) and other signaling molecules to orchestrate the complex defense signaling. Using advanced biotechnological tools, the role of Ca2+ signaling during plant-microbe interactions and the role of CaM/CMLs and CDPKs in plant defense mechanism has been revealed to some extent. The Emerging perspectives on calcium signaling in plant-microbe interactions suggest that this complex interplay could be harnessed to improve plant resistance against pathogenic microbes. We present here an overview of current understanding in calcium signatures during plant-microbe interaction so as to imbibe a future direction of research.

Beyond NPK: Mineral Nutrient-Mediated Modulation in Orchestrating Flowering Time

Flowering time in plants is a complex process regulated by environmental conditions such as photoperiod and temperature, as well as nutrient conditions. While the impact of major nutrients like nitrogen, phosphorus, and potassium on flowering time has been well recognized, the significance of micronutrient imbalances and their deficiencies should not be neglected because they affect the floral transition from the vegetative stage to the reproductive stage. The secondary major nutrients such as calcium, magnesium, and sulfur participate in various aspects of flowering. Micronutrients such as boron, zinc, iron, and copper play crucial roles in enzymatic reactions and hormone biosynthesis, affecting flower development and reproduction as well. The current review comprehensively explores the interplay between microelements and flowering time, and summarizes the underlying mechanism in plants. Consequently, a better understanding of the interplay between microelements and flowering time will provide clues to reveal the roles of microelements in regulating flowering time and to improve crop reproduction in plant industries.

Phytomelatonin: A key regulator of redox and phytohormones signaling against biotic/abiotic stresses

Plants being sessile in nature, are exposed to unwarranted threats as a result of constantly changing environmental conditions. These adverse factors can have negative impacts on their growth, development, and yield. Hormones are key signaling molecules enabling cells to respond rapidly to different external and internal stimuli. In plants, melatonin (MT) plays a critical role in the integration of various environmental signals and activation of stress-response networks to develop defense mechanisms and plant resilience. Additionally, melatonin can tackle the stress-induced alteration of cellular redox equilibrium by regulating the expression of redox hemostasis-related genes and proteins. The purpose of this article is to compile and summarize the scientific research pertaining to MT's effects on plants' resilience to biotic and abiotic stresses. Here, we have summarized that MT exerts a synergistic effect with other phytohormones, for instance, ethylene, jasmonic acid, and salicylic acid, and activates plant defense-related genes against phytopathogens. Furthermore, MT interacts with secondary messengers like Ca²⁺, nitric oxide, and reactive oxygen species to regulate the redox network. This interaction triggers different transcription factors to alleviate stress-related responses in plants. Hence, the critical synergic role of MT with diverse plant hormones and secondary messengers demonstrates phytomelatonin's importance in influencing multiple mechanisms to contribute to plant resilience against harsh environmental factors.

Supplementation of the Plant Conditioner ELICE Vakcina® Product with β-Aminobutyric Acid and Salicylic Acid May Lead to Trans-Priming Signaling in Barley (Hordeum vulgare)

Plant immunological memory, priming, is a defense mechanism that can be triggered by external stimuli, leading to the activation of biochemical pathways and preparing plants for disease resistance. Plant conditioners improve yield and crop quality through nutrient efficiency and abiotic stress tolerance, which is enhanced by the addition of resistance- and priming-induced compounds. Based on this hypothesis, this study aimed to investigate plant responses to priming actives of different natures, including salicylic acid and beta-aminobutyric acid, in combination with the plant conditioning agent ELICE Vakcina^®. Phytotron experiments and RNA-Seq analyses of differentially expressed genes using the combinations of these three investigated compounds were performed in a barley culture to investigate possible synergistic relationships in the genetic regulatory network. The results indicated a strong regulation of defense responses, which was enhanced by supplemental treatments; however, both synergistic and antagonistic effects were enhanced with one or two components, depending on the supplementation. The overexpressed transcripts were functionally annotated to assess their involvement in jasmonic acid and salicylic acid signaling; however, their determinant genes were highly dependent on the supplemental treatments. Although the effects overlapped, the potential effects of trans-priming the two supplements tested could be largely separated.

Growth or survival: What is the role of calmodulin-like proteins in plant?

Calcium signalling, including pulse, amplitude, and duration, is essential for plant development and response to various stimuli. However, the calcium signalling should be decoded and translated by calcium sensors. In plants, three classes of calcium-binding proteins have been identified as calcium sensors, including calcium-dependent protein kinase (CDPK), calcineurin B-like protein (CBL), and calmodulin (CaM). Calmodulin-like proteins (CMLs), which have several EF-hands, also serve as specific calcium sensors and can sense, bind, and interpret the calcium signal during the plant's growth and defense decision-making processes. In recent decades, the function of CMLs in plant development and response to various stimuli has been systematically reviewed, shedding light on the molecular mechanism of plant CML-mediated networks in calcium signal transduction. Here, by providing an overview of CML expression and biological function in plants, we demonstrate that growth-defense trade-offs occur during calcium sensing, an aspect that has not been well studied in recent years.

Genome-Wide Identification and Expression Analysis of Calmodulin-Like Gene Family in Paspalums vaginatium Revealed Their Role in Response to Salt and Cold Stress

The calmodulin-like (CML) family is an important calcium (Ca²⁺) sensor in plants and plays a pivotal role in the response to abiotic and biotic stresses. As one of the most salt-tolerant grass species, Paspalums vaginatum is resistant to multiple abiotic stresses, such as salt, cold, and drought. However, investigations of PvCML proteins in P. vaginatum have been limited. Based on the recently published P. vaginatum genome, we identified forty-nine PvCMLs and performed a comprehensive bioinformatics analysis of PvCMLs. The main results showed that the PvCMLs were unevenly distributed on all chromosomes and that the expansion of PvCMLs was shaped by tandem and segmental duplications. In addition, cis-acting element analysis, expression profiles, and qRT-PCR analysis revealed that PvCMLs were involved in the response to salt and cold stress. Most interestingly, we found evidence of a tandem gene cluster that independently evolved in P. vaginatum and may participate in cold resistance. In summary, our work provides important insight into how grass species are resistant to abiotic stresses such as salt and cold and could be the basis of further gene function research on CMLs in P. vaginatum.

Genome-wide analysis of the CML gene family and its response to melatonin in common bean (Phaseolus vulgaris L.)

Calmodulin-like proteins (CML) are important calcium signal transduction proteins in plants. CML genes have been analyzed in several plants. However, little information on CML in Phaseolus vulgare is available. In this study, we identified 111 PvCMLs distributed on eleven chromosomes. Phylogenetic analysis classified them into seven subfamilies. Cis-acting element prediction showed that PvCML contained elements related to growth and development, response to abiotic stress and hormones. Moreover, the majority of PvCMLs showed different expression patterns in most of the nine tissues and developmental stages which indicated the role of PvCML in the growth and development of common bean. Additionally, the common bean was treated with melatonin by seed soaking, and root transcriptome at the 5th day and qRT-PCR of different tissue at several stages were performed to reveal the response of PvCML to the hormone. Interestingly, 9 PvCML genes of subfamily VI were detected responsive to exogenous melatonin, and the expression dynamics of nine melatonin response PvCML genes after seed soaking with melatonin were revealed. Finally, the protein interaction network analysis of nine melatonin responsive PvCMLs was constructed. The systematic analysis of the PvCML gene family provides theoretical support for the further elucidation of their functions, and melatonin response molecular mechanism of the CML family in P. vulgaris.

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.

Genome-wide identification and expression analysis of calmodulin and calmodulin-like genes in wheat (Triticum aestivum L.)

Calmodulin (CaM) and calmodulin-like (CML) genes are widely involved in plant growth and development and mediating plant stress tolerance. However, the whole genome scale studies about CaM and CML gene families have not been done in wheat, and the possible functions of most wheat CaM/CML gene members are still unknown. In this study, a total of 18 TaCaM and 230 TaCML gene members were identified in wheat genome. Among these genes, 28 TaCaM/CML gene members have 74 duplicated copies, while 21 genes have 48 transcript variants, resulting in 321 putative TaCaM/CML transcripts totally. Phylogenetic tree analysis showed that they can be classified into 7 subfamilies. Similar gene structures and protein domains can be found in members of the same gene cluster. The TaCaM/CML genes were spread among all 21 chromosomes with unbalanced distributions, while most of the gene clusters contained 3 homoeologous genes located in the same homoeologous chromosome group. Synteny analysis showed that most of TaCaM/CMLs gene members can be found with 1-4 paralogous genes in T. turgidum and Ae. Tauschii. High numbers of cis-acting elements related to plant hormones and stress responses can be observed in the promoters of TaCaM/CMLs. The spatiotemporal expression patterns showed that most of the TaCaM/TaCML genes can be detected in at least one tissue. The expression levels of TaCML17, 21, 30, 50, 59 and 75 in the root or shoot can be up-regulated by abiotic stresses, suggesting that TaCML17, 21, 30, 50, 59 and 75 may be related with responses to abiotic stresses in wheat. The spatiotemporal expression patterns of TaCaM/CML genes indicated they may be involved widely in wheat growth and development. Our results provide important clues for exploring functions of TaCaMs/CMLs in growth and development as well as responses to abiotic stresses in wheat in the future.

Heterologous expression of the TaPI-PLC1-2B gene enhanced drought and salt tolerance in transgenic rice seedlings

Drought and salt stress are important factors that affect plant growth and development and cause crop yield reductions worldwide. Phospholipase C is a class of enzymes that can hydrolyze phospholipids, and it has been shown to play an important role in plant growth regulation and stress response. We used rice as a model to investigate the function of the wheat TaPI-PLC1-2B gene in salt and drought tolerance. For this purpose, we heterologously expressed the TaPI-PLC1-2B gene in rice and studied the transcriptional differences in transgenic and wide-type rice plants in the presence and absence of drought and salt stress. Our results showed that 2130 and 1759 genes expressed differentially in the TaPI-PLC1-2B overexpression rice line under salt and drought stress, respectively. Gene ontology enrichment results showed that differentially expressed genes (DEGs) were significantly enriched in cellular process, metabolic process, stimulus-response, cell, organelle, catalytic activity, and other functional processes under salt and drought stress. In addition, the Kyoto Encyclopedia of Genes and Genomes pathway analysis showed DEG enrichment in plant-pathogen interaction, phosphoinositol, plant hormones, and other signaling pathways under the two stress treatments. Furthermore, the chromosomal localization of salt and drought stress-responsive DEGs showed a clear distribution pattern on specific rice chromosomes. For instance, the greatest number of drought stress-responsive genes mapped to rice chromosomes 1 and 6. The current analysis has built the basis for future explorations to decipher the TaPI-PLC1-2B-mediated plant stress response mechanism in the relatively challenging wheat system.

Enhanced Resistance to Sclerotinia sclerotiorum in Brassica rapa by Activating Host Immunity through Exogenous Verticillium dahliae Aspf2-like Protein (VDAL) Treatment

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most destructive diseases in Brassica rapa. Verticillium dahliae Aspf2-like protein (VDAL) is a secretory protein of V. dahliae which has been shown to enhance the resistance against fungal infections in several plants. Nonetheless, the molecular mechanisms of VDAL-primed disease resistance are still poorly understood. In this study, we performed physiological, biochemical, and transcriptomic analyses of Brassica rapa in order to understand how VDAL confers resistance to S. sclerotiorumn infections in plants. The results showed that foliar application of VDAL significantly reduced the plaque area on leaves inoculated with S. sclerotiorum. It also enhanced antioxidant capacity by increasing activities of superoxide dismutase (SOD), peroxidase (POD), peroxidase (APX), glutathione reductase (GR), protoporphyrinogen oxidase (PPO), and defense-related enzymes β-1,3-glucanase and chitinase during the infection periods. This occurred in parallel with significantly reduced relative conductivity at different periods and lower malondialdehyde (MDA) content as compared to sole S. sclerotiorum inoculation. Transcriptomic analysis showed a total of 146 (81 up-regulated and 65 down-regulated) differentially expressed genes (DEGs) in VDAL-treated leaves compared to the control. The most enriched three Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were the mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, and plant-pathogen interaction, all of which were associated with plant immunity. DEGs associated with MAPK and hormone signal transduction pathways were ethylene response sensor ERS2, EIN3 (Ethylene Insensitive3)-binding F-box protein 2 (EBF2), ethylene-responsive transcription factor ERF94, MAPK 9 (MKK9), protein phosphatase 2C (PP2C37), auxin-responsive proteins (AUX/IAA1 and 19), serine/threonine-protein kinase CTR1, and abscisic acid receptors (PLY 4 and 5). Among the DEGs linked with the plant-pathogen interaction pathway were calmodulin-like proteins (CML5, 24, 27), PTI1-like tyrosine protein kinase 3 (Pti13) and transcription factor MYB30, all of which are known to play key roles in pathogen-associated molecular pattern (PAMP)-triggered immunity and effector-triggered immunity (ETI) for hypersensitive response (HR), cell wall reinforcement, and stomatal closure in plants. Overall, VDLA treatment triggered repression of the auxin and ABA signaling pathways and de-repression of the ethylene signaling pathways in young B. rapa seedlings to increase plant innate immunity. Our results showed that VDAL holds great potential to enhance fungal disease resistance in B. rapa crop.

Identification of the OsCML4 Gene in Rice Related to Salt Stress Using QTL Analysis

Soil salinity is a major abiotic stress that causes disastrous losses in crop yields. To identify favorable alleles that enhance the salinity resistance of rice (Oryza sativa L.) crops, a set of 120 Cheongcheong Nagdong double haploid (CNDH) lines derived from a cross between the Indica variety Cheongcheong and the Japonica variety Nagdong were used. A total of 23 QTLs for 8 different traits related to salinity resistance on chromosomes 1–3 and 5–12 were identified at the seedling stage. A QTL related to the salt injury score (SIS), qSIS-3b, had an LOD score of six within the interval RM3525–RM15904 on chromosome 3, and a phenotypic variation of 31% was further examined for the candidate genes. Among all the CNDH populations, five resistant lines (CNDH 27, CNDH 34-1, CNDH 64, CNDH 78, and CNDH 112), five susceptible lines (CNDH 52-1, CNDH 67, CNDH 69, CNDH 109, and CNDH 110), and the parent lines Cheongcheong and Nagdong were selected for relative gene expression analysis. Among all the genes, two candidate genes were highly upregulated in resistant lines, including the auxin-responsive protein IAA13 (Os03g0742900) and the calmodulin-like protein 4 (Os03g0743500-1). The calmodulin-like protein 4 (Os03g0743500-1) showed a higher expression in all the resistant lines than in the susceptible lines and a high similarity with other species in sequence alignment and phylogenetic tree, and it also showed a protein–protein interaction with other important proteins. The genes identified in our study will provide new genetic resources for improving salt resistance in rice using molecular breeding strategies in the future.

WRKY63 transcriptional activation of COOLAIR and COLDAIR regulates vernalization-induced flowering

Arabidopsis (Arabidopsis thaliana) FLOWERING LOCUS C (FLC) acts as a key flowering regulator by repressing the expression of the floral integrator FLOWERING LOCUS T (FT). Prolonged exposure to cold (vernalization) induces flowering by reducing FLC expression. The long noncoding RNAs (lncRNAs) COOLAIR and COLDAIR, which are transcribed from the 3' end and the first intron of FLC, respectively, are important for FLC repression under vernalization. However, the molecular mechanism of how COOLAIR and COLDAIR are transcriptionally activated remains elusive. In this study, we found that the group-III WRKY transcription factor WRKY63 can directly activate FLC. wrky63 mutant plants display an early flowering phenotype and are insensitive to vernalization. Interestingly, we found that WRKY63 can activate the expression of COOLAIR and COLDAIR by binding to their promoters.WRKY63 therefore acts as a dual regulator that activates FLC directly under non-vernalization conditions but represses FLC indirectly during vernalization through inducing COOLAIR and COLDAIR. Furthermore, genome-wide occupancy profile analyses indicated that the binding of WRKY63 to vernalization-induced genes increases after vernalization. In addition, WRKY63 binding is associated with decreased levels of the repressive marker Histone H3 Lysine 27 trimethylation (H3K27me3). Collectively, our results indicate that WRKY63 is an important flowering regulator involved in vernalization-induced transcriptional regulation.

Multiple roles of wheat calmodulin genes during stress treatment and TaCAM2-D as a positive regulator in response to drought and salt tolerance

Calmodulin (CaM) and calmodulin-like (CML) proteins are the most prominent calcium (Ca²⁺) sensing proteins involved in Ca²⁺-signaling processes. However, the function of these calcium sensors in wheat remains unclear. In this study, 15 TaCAMs and 113 TaCMLs were identified from the wheat reference genome. The analysis of cis-acting elements and expression patterns showed that TaCAMs might play an important role in response to abiotic and biotic stresses. TaCAM2-D gene was found to be significantly upregulated under drought and salt stresses, and thus, it was selected to further explore the biological function. Moreover, TaCAM2-D was observed to be localized in the nucleus, membrane and cytoplasm. Overexpression of TaCAM2-D in Arabidopsis conferred greater tolerance to drought and salt. The prediction analysis, the yeast two-hybrid analysis, and bimolecular fluorescence complementation assay indicated that TaCAM2-D interacted with TaMPK8, which is one of the wheat mitogen-activated protein kinases. Thus, the current study provides insights into the understanding of the TaCAM and TaCML genes in wheat.

A calcification-related calmodulin-like protein in the oyster Crassostrea gigas mediates the enhanced calcium deposition induced by CO2 exposure

Calcium transportation and homeostasis are essential for marine bivalves to maintain basic metabolism and build their shells. Calmodulin-like proteins (CaLPs) are important calcium sensors and buffers and can respond to ocean acidification (OA) in marine calcifiers. However, no further study of their physiological function in calcium metabolism under elevated CO₂ has been performed. Here, we identified a novel CaLP (designated CgCaLP) in the Pacific oyster Crassostrea gigas and demonstrated its participation in the calcification process: the mRNA expression level of CgCaLP peaked at the trochophore larval stage and remained high at stages when shells were shaped; the mRNA and protein of CgCaLP were more highly expressed in mantle tissue than in other tissues. Under elevated CO₂ levels, the protein expression level of CgCaLP in hemocytes increased, while in contrast, significantly decreased protein levels were detected in gill and mantle tissues. Shell dissolution caused the imbalance of calcium in hemocytes and decreased calcium absorption and transportation demand in gill and mantle tissues, inducing the molecular function allocation of CgCaLP under CO₂ exposure. Despite the decreased protein level in mantle tissue, CgCaLP was found to translocate to outer mantle epithelium (OME) cells where condensed calcium-rich deposits (CRDs) were detected. We further demonstrated that CgCaLP mRNA and protein expression levels could respond to seawater Ca²⁺ availability, suggesting that the calcium deposition capacity of oysters might be enhanced to fight against shell dissolution problems and that CgCaLP might serve as an essential participator of the process. In summary, CgCaLP might enhance calcium deposition under CO₂ exposure and thus play a significant and flexible molecular function involved in a compensation strategy of oysters to fight against the acidified ocean.

The Ca2+ sensor proteins CML37 and CML42 antagonistically regulate plant stress responses by altering phytohormone signals

Calmodulin-like-proteins (CML) belong to a family of calcium-sensing proteins that are unique for plants and involved in many different developmental and stress-related reactions. In defense against herbivory, some pathogens and drought, CML37 acts as a positive and CML42 as a negative regulator, respectively. We provide evidence that both CMLs act antagonistically in the regulation of induced defense responses. A double knock-out line, cml37 x cml42, thus shows wild-type phenotypes upon all kind of stresses we used. A transient increase in the cytosolic calcium concentration is one of the first reactions that can be measured in plant cells upon abiotic as well as biotic stress treatments. These calcium signals are sensed by calcium binding proteins such as calmodulin-like proteins (CMLs), which transduce the sensed information into appropriate stress responses by interacting with downstream target proteins. In previous studies, CML37 has been shown to positively regulate the plants' defense against both the insect herbivore Spodoptera littoralis and the response to drought stress. In contrast, CML42 is known to negatively regulate those two stress responses. Here, we provide evidence that these two CMLs act antagonistically in the regulation of induced responses directed against drought and herbivory stress as well as in the defense against the necrotrophic pathogen Alternaria brassicicola. Both CMLs shape the plant reactions by altering the phytohormone signaling. Consequently, the phytohormone-regulated production of defensive compounds like glucosinolates is also antagonistically mediated by both CMLs. The finding that CML37 and CML42 have antagonistic roles in diverse stress-related responses suggests that these calcium sensor proteins represent important tools for the plant to balance and fine-tune the signaling and downstream reactions upon environmental stress.

Genome-Wide Identification and Expression Analysis of CsCaM/CML Gene Family in Response to Low-Temperature and Salt Stresses in Chrysanthemum seticuspe

Calmodulin (CaM) and calmodulin-like proteins (CML) act as significant Ca²⁺ sensors binding Ca²⁺ with EF-hand motifs and have been reported to be involved in various environmental stresses in plants. In this study, calmodulin CsCaM/CML gene family members were identified based on the genome of Chrysanthemum seticuspe published recently; a phylogenetic tree was constructed; gene structures and chromosomal locations of CsCaM/CML were depicted; cis-acting regulatory elements were predicted; collinearity and duplicate events of CaM/CML were analyzed using MCScanX software; and the expression levels of CsCaM/CML in response to abiotic stress were analyzed, based on the published RNA-seq data. We identified 86 CsCaM/CML (4 CsCaMs and 82 CsCMLs) genes in total. Promoter sequences of CsCaM/CML contained elements related to abiotic stresses (including low-temperature and anaerobic stresses) and plant hormones (including abscisic acid (ABA), MeJA, and salicylic acid). CsCaM/CML genes were distributed on nine chromosomes unevenly. Collinearity analysis indicated that recent segmental duplications significantly enlarged the scale of the CML family in C. seticuspe. Four CsCMLs (CsCML14, CsCML50, CsCML65, and CsCML79) were statistically differentially regulated under low-temperature and salt stress compared with those in the normal condition. These results indicate diverse roles of CsCaM/CML in plant development and in response to environmental stimuli in C. seticuspe.

Comprehensive analysis of 1R- and 2R-MYBs reveals novel genic and protein features, complex organisation, selective expansion and insights into evolutionary tendencies

Myeloblastosis (MYB) family, the largest plant transcription factor family, has been subcategorised based on the number and type of repeats in the MYB domain. In spite of several reports, evolution of MYB genes and repeats remains enigmatic. Brassicaceae members are endowed with complex genomes, including dysploidy because of its unique history with multiple rounds of polyploidisation, genomic fractionations and rearrangements. The present study is an attempt to gain insights into the complexities of MYB family diversity, understand impacts of genome evolution on gene families and develop an evolutionary framework to understand the origin of various subcategories of MYB gene family. We identified and analysed 1129 MYBs that included 1R-, 2R-, 3R- and atypical-MYBs across sixteen species representing protists, fungi, animals and plants and exclude MYB identified from Brassicaceae except Arabidopsis thaliana; in addition, a total of 1137 2R-MYB genes from six Brassicaceae species were also analysed. Comparative analysis revealed predominance of 1R-MYBs in protists, fungi, animals and lower plants. Phylogenetic reconstruction and analysis of selection pressure suggested ancestral nature of R1-type repeat containing 1R-MYBs that might have undergone intragenic duplication to form multi-repeat MYBs. Distinct differences in gene structure between 1R-MYB and 2R-MYBs were observed regarding intron number, the ratio of gene length to coding DNA sequence (CDS) length and the length of exons encoding the MYB domain. Conserved as well as novel and lineage-specific intron phases were identified. Analyses of physicochemical properties revealed drastic differences indicating functional diversification in MYBs. Phylogenetic reconstruction of 1R- and 2R-MYB genes revealed a shared structure-function relationship in clades which was supported when transcriptome data was analysed in silico. Comparative genomics to study distribution pattern and mapping of 2R-MYBs revealed congruency and greater degree of synteny and collinearity among closely related species. Micro-synteny analysis of genomic segments revealed high conservation of genes that are immediately flanking the surrounding tandemly organised 2R-MYBs along with instances of local duplication, reorganisations and genome fractionation. In summary, polyploidy, dysploidy, reshuffling and genome fractionation were found to cause loss or gain of 2R-MYB genes. The findings need to be supported with functional validation to understand gene structure-function relationship along the evolutionary lineage and adaptive strategies based on comparative functional genomics in plants.

Gene-coexpression network analysis identifies specific modules and hub genes related to cold stress in rice

Background

When plants are subjected to cold stress, they undergo a series of molecular and physiological changes to protect themselves from injury. Indica cultivars can usually withstand only mild cold stress in a relatively short period. Hormone-mediated defence response plays an important role in cold stress. Weighted gene co-expression network analysis (WGCNA) is a very useful tool for studying the correlation between genes, identifying modules with high phenotype correlation, and identifying Hub genes in different modules. Many studies have elucidated the molecular mechanisms of cold tolerance in different plants, but little information about the recovery process after cold stress is available.

Results

To understand the molecular mechanism of cold tolerance in rice, we performed comprehensive transcriptome analyses during cold treatment and recovery stage in two cultivars of near-isogenic lines (9311 and DC907). Twelve transcriptomes in two rice cultivars were determined. A total of 2509 new genes were predicted by fragment splicing and assembly, and 7506 differentially expressed genes were identified by pairwise comparison. A total of 26 modules were obtained by expression-network analysis, 12 of which were highly correlated with cold stress or recovery treatment. We further identified candidate Hub genes associated with specific modules and analysed their regulatory relationships based on coexpression data. Results showed that various plant-hormone regulatory genes acted together to protect plants from physiological damage under short-term low-temperature stress. We speculated that this may be common in rice. Under long-term cold stress, rice improved the tolerance to low-temperature stress by promoting autophagy, sugar synthesis, and metabolism.

Conclusion

Through WGCNA analysis at the transcriptome level, we provided a potential regulatory mechanism for the cold stress and recovery of rice cultivars and identified candidate central genes. Our findings provided an important reference for the future cultivation of rice strains with good tolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08438-3.

Comparative Transcriptome Analysis Reveals New Insight of Alfalfa (Medicago sativa L.) Cultivars in Response to Abrupt Freezing Stress

Freezing stress is a major limiting environmental factor that affects the productivity and distribution of alfalfa (Medicago sativa L.). There is growing evidence that enhancing freezing tolerance through resistance-related genes is one of the most efficient methods for solving this problem, whereas little is known about the complex regulatory mechanism of freezing stress. Herein, we performed transcriptome profiling of the leaves from two genotypes of alfalfa, freezing tolerance "Gannong NO.3" and freezing-sensitive "WL326GZ" exposure to -10°C to investigate which resistance-related genes could improve the freezing tolerance. Our results showed that a total of 121,366 genes were identified, and there were 7,245 differentially expressed genes (DEGs) between the control and treated leaves. In particular, the DEGs in "Gannong NO.3" were mainly enriched in the metabolic pathways and biosynthesis of secondary metabolites, and most of the DEGs in "WL326GZ" were enriched in the metabolic pathways, the biosynthesis of secondary metabolites, and plant-pathogen interactions. Moreover, the weighted gene co-expression network analysis (WGCNA) showed that ATP-binding cassette (ABC) C subfamily genes were strongly impacted by freezing stress, indicating that ABCC8 and ABCC3 are critical to develop the freezing tolerance. Moreover, our data revealed that numerous Ca2+ signal transduction and CBF/DREB1 pathway-related genes were severely impacted by the freezing resistance, which is believed to alleviate the damage caused by freezing stress. Altogether, these findings contribute the comprehensive information to understand the molecular mechanism of alfalfa adaptation to freezing stress and further provide functional candidate genes that can adapt to abiotic stress.

A Class II KNOX Gene, KNAT7-1, Regulates Physical Seed Dormancy in Mungbean [Vigna radiata (L.) Wilczek]

Seed dormancy in wild mungbean (Vigna radiata var. sublobata) may be useful for the breeding of cultivated mungbean (var. radiata) with pre-harvest sprouting resistance. Previous studies have identified two major quantitative trait loci (QTLs) for seed dormancy, HsA and Sdwa5.1.1+, in wild mungbean that are possibly having the same locus or linked. However, these QTLs have not been confirmed/verified and a molecular basis of seed dormancy in mungbean is not yet known. In this study, we aimed to finely map the Sdwa5.1.1+ and identify candidate gene(s) for this locus. Microscopic observations revealed that wild mungbean "ACC41" seeds had a palisade cuticle layer, while cultivated mungbean "Kamphaeng Saen 2" (KPS2) seeds lacked this layer. Fine mapping using an F₂ population developed from a cross between ACC41 and KPS2 revealed two linked QTLs, Sdwa5.1.1+ and Sdwa5.1.2+, controlling seed dormancy. The Sdwa5.1.1+ was confirmed in an F_2:3 population derived from the same cross and mapped to a 3.298-Kb region containing only one gene LOC106767068, designated as VrKNAT7-1, which encodes the transcription factor KNOTTED ARABIDOPSIS THALIANA7 (KNAT7), a class II KNOTTED1-LIKE HOMEOBOX (KNOX II) protein. VrKNAX7 sequence alignment between ACC41 and KPS2 revealed several polymorphisms in the coding, untranslated, and promoter regions. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of VrKNAT7-1 and VrCYP86A, a putative downstream regulation of VrKNAT7-1, in the seed coat of ACC41 is statistically much higher than that of KPS2. Altogether, these results indicate that VrKNAT7-1 controls physical seed dormancy in the wild mungbean ACC41.

Calmodulin-like protein CML24 interacts with CAMTA2 and WRKY46 to regulate ALMT1-dependent Al resistance in Arabidopsis thaliana

ALUMINUM-ACTIVATED MALATE TRANSPORTER1 (ALMT1)-mediated malate exudation from roots is critical for aluminium (Al) resistance in Arabidopsis. Its upstream molecular signalling regulation is not yet well understood. The role of CALMODULIN-LIKE24 (CML24) in Al-inhibited root growth and downstream molecular regulation of ALMT1-meditaed Al resistance was investigated. CML24 confers Al resistance demonstrated by an increased root-growth inhibition of the cml24 loss-of-function mutant under Al stress. This occurs mainly through the regulation of the ALMT1-mediated malate exudation from roots. The mutation and overexpression of CML24 leads to an elevated and reduced Al accumulation in the cell wall of roots, respectively. Al stress induced both transcript and protein abundance of CML24 in root tips, especially in the transition zone. CML24 interacts with CALMODULIN BINDING TRANSCRIPTION ACTIVATOR2 (CAMTA2) and promotes its transcriptional activity in the regulation of ALMT1 expression. This results in an enhanced malate exudation from roots and less root-growth inhibition under Al stress. Both CML24 and CAMTA2 interacted with WRKY46 suppressing the transcriptional repression of ALMT1 by WRKY46. The study provides novel insights into understanding of the upstream molecular signalling of the ALMT1-depdendent Al resistance.

Calmodulin and calmodulin-like gene family in barley: Identification, characterization and expression analyses

Calmodulin (CaM) and calmodulin-like (CML) proteins are Ca²⁺ relays and play diverse and multiple roles in plant growth, development and stress responses. However, CaM/CML gene family has not been identified in barley (Hordeum vulgare). In the present study, 5 HvCaMs and 80 HvCMLs were identified through a genome-wide analysis. All HvCaM proteins possessed 4 EF-hand motifs, whereas HvCMLs contained 1 to 4 EF-hand motifs. HvCaM2, HvCaM3 and HvCaM5 coded the same polypeptide although they differed in nucleotide sequence, which was identical to the polypeptides coded by OsCaM1-1, OsCaM1-2 and OsCaM1-3. HvCaMs/CMLs were unevenly distributed over barley 7 chromosomes, and could be phylogenetically classified into 8 groups. HvCaMs/CMLs differed in gene structure, cis-acting elements and tissue expression patterns. Segmental and tandem duplication were observed among HvCaMs/CMLs during evolution. HvCML16, HvCML18, HvCML50 and HvCML78 were dispensable genes and the others were core genes in barley pan-genome. In addition, 14 HvCaM/CML genes were selected to examine their responses to salt, osmotic and low potassium stresses by qRT-PCR, and their expression were stress-and time-dependent. These results facilitate our understanding and further functional identification of HvCaMs/CMLs.

A Comprehensive Analysis of Calmodulin-Like Proteins of Glycine max Indicates Their Role in Calcium Signaling and Plant Defense Against Insect Attack

The calcium (Ca²⁺) signaling is a crucial event during plant-herbivore interaction, which involves a transient change in cytosolic Ca²⁺ concentration, which is sensed by Ca²⁺-sensors, and the received message is transduced to downstream target proteins leading to appropriate defense response. Calmodulin-like proteins (CMLs) are calcium-sensing plant-specific proteins. Although CMLs have been identified in a few plants, they remained uncharacterized in leguminous crop plants. Therefore, a wide-range analysis of CMLs of soybean was performed, which identified 41 true CMLs with greater than 50% similarity with Arabidopsis CMLs. The phylogenetic study revealed their evolutionary relatedness with known CMLs. Further, the identification of conserved motifs, gene structure analysis, and identification of cis-acting elements strongly supported their identity as members of this family and their involvement in stress responses. Only a few Glycine max CMLs (GmCMLs) exhibited differential expression in different tissue types, and rest of them had minimal expression. Additionally, differential expression patterns of GmCMLs were observed during Spodoptera litura-feeding, wounding, and signaling compound treatments, indicating their role in plant defense. The three-dimensional structure prediction, identification of interactive domains, and docking with Ca²⁺ ions of S. litura-inducible GmCMLs, indicated their identity as calcium sensors. This study on the characterization of GmCMLs provided insights into their roles in calcium signaling and plant defense during herbivory.

Molecular Evolution of Calcium Signaling and Transport in Plant Adaptation to Abiotic Stress

Adaptation to unfavorable abiotic stresses is one of the key processes in the evolution of plants. Calcium (Ca2+) signaling is characterized by the spatiotemporal pattern of Ca2+ distribution and the activities of multi-domain proteins in integrating environmental stimuli and cellular responses, which are crucial early events in abiotic stress responses in plants. However, a comprehensive summary and explanation for evolutionary and functional synergies in Ca2+ signaling remains elusive in green plants. We review mechanisms of Ca2+ membrane transporters and intracellular Ca2+ sensors with evolutionary imprinting and structural clues. These may provide molecular and bioinformatics insights for the functional analysis of some non-model species in the evolutionarily important green plant lineages. We summarize the chronological order, spatial location, and characteristics of Ca2+ functional proteins. Furthermore, we highlight the integral functions of calcium-signaling components in various nodes of the Ca2+ signaling pathway through conserved or variant evolutionary processes. These ultimately bridge the Ca2+ cascade reactions into regulatory networks, particularly in the hormonal signaling pathways. In summary, this review provides new perspectives towards a better understanding of the evolution, interaction and integration of Ca2+ signaling components in green plants, which is likely to benefit future research in agriculture, evolutionary biology, ecology and the environment.

A novel Medicago truncatula calmodulin-like protein (MtCML42) regulates cold tolerance and flowering time

Calmodulin-like proteins (CMLs) are one of the Ca²⁺ sensors in plants, but the functions of most CMLs remain unknown. The regulation of cold tolerance and flowering time by MtCML42 in Medicago truncatula and the underlying mechanisms were investigated using MtCML42-overexpressing plants and cml42 Medicago mutants with a Tnt1 retrotransposon insertion. Compared with the wild type (WT), MtCML42-overexpressing lines had increased cold tolerance, whereas cml42 mutants showed decreased cold tolerance. The impaired cold tolerance in cml42 could b complemented by MtCML42 expression. The transcript levels of MtCBF1, MtCBF4, MtCOR413, MtCAS15, MtLTI6A, MtGolS1 and MtGolS2 and the concentrations of raffinose and sucrose were increased in response to cold treatment, whereas higher levels were observed in MtCML42-overexpressing lines and lower levels were observed in cml42 mutants. In addition, early flowering with upregulated MtFTa1 and downregulated MtABI5 transcripts was observed in MtCML42-overexpressing lines, whereas delayed flowering with downregulated MtFTa1 and upregulated MtABI5 was observed in cml42. MtABI5 expression could complement the flowering phenotype in the Arabidopsis mutant abi5. Our results suggest that MtCML42 positively regulates MtCBF1 and MtCBF4 expression, which in turn upregulates the expression of some COR genes, MtGolS1 and MtGolS2, which leads to raffinose accumulation and increased cold tolerance. MtCML42 regulates flowering time through sequentially downregulating MtABI5 and upregulating MtFTa1 expression.

Characteristics of SlCML39, a Tomato Calmodulin-like Gene, and Its Negative Role in High Temperature Tolerance of Arabidopsis thaliana during Germination and Seedling Growth

Calmodulin-like (CML) proteins are primary calcium sensors and function in plant growth and response to stress stimuli. However, so far, the function of plant CML proteins, including tomato, is still unclear. Previously, it was found that a tomato (Solanum lycopersicum) CML, here named SlCML39, was significantly induced by high temperature (HT) at transcription level, but its biological function is scarce. In this study, the characteristics of SlCML39 and its role in HT tolerance were studied. SlCML39 encodes a protein of 201 amino acids containing four EF hand motifs. Many cis-acting elements related to plant stress and hormone response appear in the promoter regions of SlCML39. SlCML39 is mainly expressed in the root, stem, and leaf and can be regulated by HT, cold, drought, and salt stresses as well as ABA and H₂O₂. Furthermore, heterologous overexpression of SlCML39 reduces HT tolerance in Arabidopsis thaliana at the germination and seedling growth stages. To better understand the molecular mechanism of SlCML39, the downstream gene network regulated by SlCML39 under HT was analyzed by RNA-Seq. Interestingly, we found that many genes involved in stress responses as well as ABA signal pathway are down-regulated in the transgenic seedlings under HT stress, such as KIN1, RD29B, RD26, and MAP3K18. Collectively, these data indicate that SlCML39 acts as an important negative regulator in response to HT stress, which might be mediated by the ABA signal pathway.

Alfalfa (Medicago sativa L.) MsCML46 gene encoding calmodulin-like protein confers tolerance to abiotic stress in tobacco

KEY MESSAGE

MsCML46 enhances tolerance to abiotic stresses through alleviating osmotic stress and oxidative damage by regulating the expression of stress-related genes to optimize osmolytes levels and antioxidant enzyme activity in transgenic tobacco. Abiotic stresses are major environmental factors that constraint crop productivity worldwide. Various stimuli regulate intracellular calcium levels and calcium-mediated signal transduction, and cellular responses. Ca2+ signals are perceived by different Ca2+ receptors. Calmodulin-like protein (CML) is one of the best-characterized Ca2+ sensors which shares sequence similarity with highly conserved calmodulin (CaM) ubiquitously expressed in plants. Currently, the molecular and physiological functions of CMLs are largely unknown. In this study, the MsCML46 was characterized in alfalfa (Medicago sativa cv. Zhaodong) under freezing stress. Results showed that MsCML46 was localized to the cytoplasm of Arabidopsis, and its expression was strongly elevated by cold, drought, salt, saline-alkali, and ABA treatments. Overexpressing MsCML46 in tobacco enhanced tolerance to freezing, drought, and salt stresses as evidenced by improved contents of osmotic regulatory solutes and antioxidant enzyme activity but decreased reactive oxygen species (ROS) accumulation. Furthermore, cold, drought, and salt stresses increased the expression of stress-related genes in transgenic tobacco. MsCML46 binds free Ca2+ to promote signal transduction and maintain higher K+/Na+ ratio. In this way, it protects intracellular homeostasis under sodium ion toxicity. These results suggest that MsCML46 plays a crucial role in resisting abiotic stresses and can be exploited in genetic engineering for crops.

The Mildew Resistance Locus O 4 Interacts with CaM/CML and Is Involved in Root Gravity Response

The plant-specific mildew resistance locus O (MLO) proteins, which contain seven transmembrane domains and a conserved calmodulin-binding domain, play important roles in many plant developmental processes. However, their mechanisms that regulate plant development remain unclear. Here, we report the functional characterization of the MLO4 protein in Arabidopsis roots. The MLO4 was identified as interacting with CML12 in a screening for the interaction between the proteins from Arabidopsis MLO and calmodulin/calmodulin-like (CaM/CML) families using yeast two hybrid (Y2H) assays. Then, the interaction between MLO4 and CML12 was further verified by Luciferase Complementation Imaging (LCI) and Bimolecular Fluorescence Complementation (BiFC) assays. Genetic analysis showed that the mlo4, cml12, and mlo4 cml12 mutants displayed similar defects in root gravity response. These results imply that the MLO4 might play an important role in root gravity response through interaction with CML12. Moreover, our results also demonstrated that the interaction between the MLO and CaM/CML families might be conservative.

Isolation and Functional Characterization of a Salt-Responsive Calmodulin-Like Gene MpCML40 from Semi-Mangrove Millettia pinnata

Salt stress is a major increasing threat to global agriculture. Pongamia (Millettia pinnata), a semi-mangrove, is a good model to study the molecular mechanism of plant adaptation to the saline environment. Calcium signaling pathways play critical roles in the model plants such as Arabidopsis in responding to salt stress, but little is known about their function in Pongamia. Here, we have isolated and characterized a salt-responsive MpCML40, a calmodulin-like (CML) gene from Pongamia. MpCML40 protein has 140 amino acids and is homologous with Arabidopsis AtCML40. MpCML40 contains four EF-hand motifs and a bipartite NLS (Nuclear Localization Signal) and localizes both at the plasma membrane and in the nucleus. MpCML40 was highly induced after salt treatment, especially in Pongamia roots. Heterologous expression of MpCML40 in yeast cells improved their salt tolerance. The 35S::MpCML40 transgenic Arabidopsis highly enhanced seed germination rate and root length under salt and osmotic stresses. The transgenic plants had a higher level of proline and a lower level of MDA (malondialdehyde) under normal and stress conditions, which suggested that heterologous expression of MpCML40 contributed to proline accumulation to improve salt tolerance and protect plants from the ROS (reactive oxygen species) destructive effects. Furthermore, we did not observe any measurable discrepancies in the development and growth between the transgenic plants and wild-type plants under normal growth conditions. Our results suggest that MpCML40 is an important positive regulator in response to salt stress and of potential application in producing salt-tolerant crops.

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.

Calmodulin binding transcription activators: An interplay between calcium signalling and plant stress tolerance

In plants, next to the secondary messengers lies an array of signal relaying molecules among which Calmodulins convey the unequivocal alarms of calcium influxes to Calmodulin-Binding Transcription Activators (CAMTA). Upon reception, CAMTA transcription factors decode the calcium signatures by transcribing the genes corresponding to the specific stimulus, thus have direct/indirect engagement in the complex signalling crosstalk. CAMTA transcription factors make an important contribution to the genome of all eukaryotes, including plants, from Brassica napus (18) to Carica papaya (2), the number of CAMTA genes varies across the plant species, however they exhibit a similar evolutionarily conserved domain organization including a DNA-Binding Domain (CG-1), a Transcription Factor Immunoglobulin Binding Domain (TIG), a Calmodulin-Binding Domain (CaMBD/IQ) and several Ankyrin repeats. The regulatory region of CAMTA genes possess multiple stress-responsive cis motifs including ABRE, SARE, G-box, W-box, AuXRE, DRE and others. CAMTA TFs in Arabidopsis have been studied extensively, however in other plants (with a few exceptions), the evidence merely bases upon expression analyses. CAMTAs are reported to orchestrate biotic as well as abiotic stresses including those occurring due to water and temperature fluctuations as well as heavy metals, light and salinity. Through CG-1 domain, CAMTA TFs bind the CG-box in the promoter of their target genes and modulate their expression under adverse conditions. Here we present a glimpse of how calcium signatures are coded and decoded and translated into necessary responses. In addition, we have emphasized on exploitation of the multiple-stress responsive nature of CAMTAs in engineering plants with desired traits.

Genome-wide identification and expression analysis of CaM/CML genes in Brassica napus under abiotic stress

Calmodulin (CaM) and calmodulin-like (CML) proteins are primary calcium (Ca²⁺) sensors and are involved in the regulation of plant development and stress responses by converting calcium signals into transcriptional responses, protein phosphorylation, or metabolic changes. However, the characterization and expression profiling of CaM/CML genes in Brassica napus remain limited. The present study reports that 25 BnaCaM and 168 BnaCML genes were identified in B. napus. The phylogenetics, gene structures, gene motifs, gene chromosomal locations, syntenic and Ka/Ks analysis, promoter cis-acting elements, and expression characteristics in various organs and under abiotic stress were evaluated. The phylogenetic results revealed a total of 11 subgroups, including one unique clade of CaMs distinct from CMLs. Most of group I (CaM), II, III, and X members are intron rich, while members from the other seven groups are intron-less. The majority of CaM/CML proteins have four EF-hands. Syntenic analysis showed that 91.3 % orthologous CaM/CML gene pairs between B. rapa and B. oleracea were retained as homologous gene pairs in B. napus. Ka/Ks analysis indicated that the majority of BnaCaM/CML experienced purifying selection. Expression analysis showed that BnaCaMs genes are highly and ubiquitously expressed in all of the organs and tissues examined, while distinct BnaCMLs are expressed specifically in particular organs and tissues. In total, 129 BnaCaM/CML were induced by abiotic stress and phytohormones. BnaCMLs from group IV, VI, VIII, and X were strongly induced by freezing treatment, but were not or just slightly induced by chilling treatment. The present study is the first to analyze the CaM/CML gene family in B. napus, which is useful for understanding the functions of the BnaCaM/CML in modulating plant responses to abiotic stress, especially freezing stress.

Calmodulin-Like (CML) Gene Family in Medicago truncatula: Genome-Wide Identification, Characterization and Expression Analysis

Calcium is an important second messenger in mediating adaptation responses of plants to abiotic and biotic stresses. Calmodulin-like (CML) protein is an important calcium-signaling protein that can sense and decode Ca2+ signal in plants. Medicago truncatula is a model legume plant; however, investigations of MtCML proteins are limited. Using genome analysis and BLAST database searches, fifty MtCML proteins that possess EF-hand motifs were identified. Phylogenetic analysis showed that CML homologs between M. truncatula, Arabidopsis thaliana and Oryza sativa shared close relationships. Gene structure analysis revealed that these MtCML genes contained one to four conserved EF-hand motifs. All MtCMLs are localized to eight chromosomes and underwent gene duplication. In addition, MtCML genes were differentially expressed in different tissues of M. truncatula. Cis-acting elements in promoter region and expression analysis revealed the potential response of MtCML protein to abiotic stress and hormones. The results provide a basis of further functional research on the MtCML gene family and facilitate their potential use for applications in the genetic improvement on M. truncatula in drought, cold and salt stress environments.

QTL mapping for pre-harvest sprouting resistance in japonica rice varieties utilizing genome re-sequencing

Pre-harvest sprouting (PHS) leads to serious economic losses because of reductions in yield and quality. To analyze the quantitative trait loci (QTLs) for PHS resistance in japonica rice, PHS rates on panicles were measured in 160 recombinant inbred lines (RILs) derived from a cross between the temperate japonica varieties Odae (PHS resistant) and Unbong40 (PHS susceptible) under two different environmental conditions—field (summer) and greenhouse (winter) environments. Genome re-sequencing of the parental varieties detected 266,773 DNA polymorphisms including 248,255 single nucleotide polymorphisms and 18,518 insertions/deletions. We constructed a genetic map comprising 239 kompetitive allele-specific PCR and 49 cleaved amplified polymorphic sequence markers. In the field environment, two major QTLs, qPHS-3^FD and qPHS-11^FD, were identified on chromosomes 3 and 11, respectively, whereas three major QTLs, qPHS-3^GH, qPHS-4^GH, and qPHS-11^GH, were identified on chromosomes 3, 4, and 11, respectively, in the greenhouse environment. qPHS-11^GH and qPHS-11^FD had similar locations on chromosome 11, suggesting the existence of a gene conferring stable PHS resistance effects under different environmental conditions. The QTLs identified in this study can be used to improve the PHS resistance of japonica varieties, and they may improve our understanding of the genetic basis of PHS resistance.

Identification, characterization and expression analysis of calmodulin and calmodulin-like proteins in Solanum pennellii

In plants, the calmodulin (CaM) proteins is an important calcium-binding protein, which play a crucial role in both regulating plant growth and development, as well as in the resistance mechanisms to various biotic and abiotic stresses. However, there is limited knowledge available on the CaM family functions in Solanum pennellii, a wild tomato species utilized as a genetic resource for cultivated tomatoes. In this study, 6 CaM (SpCaM) and 45 CaM-like (SpCML) genes from Solanum pennellii were selected for bioinformatics analysis to obtain insights into their phylogenetic relationships, gene structures, conserved motifs, chromosomal locations, and promoters. The results showed that the 6 SpCaM proteins contained 4 EF-hand domains each, and the 45 SpCML proteins had 2-4 EF-hand domains. The 51 CaM and CaM-like genes contained different intron/exon patterns and they were unevenly distributed across the 12 chromosomes of S. pennellii. The results of the analysis of the conserved motifs and promoter cis-regulatory elements also indicated that these proteins were involved in the responses to biotic and abiotic stresses. qRT-PCR analysis indicated that the SpCaM and SpCML genes had broad expression patterns in abiotic stress conditions and with hormone treatments, in different tissues. The findings of this study will be important for further investigations of the calcium signal transduction mechanisms under stress conditions and lay a theoretical foundation for further exploration of the molecular mechanisms of plant resistance.

AsHSP26.8a, a creeping bentgrass small heat shock protein integrates different signaling pathways to modulate plant abiotic stress response

BACKGROUND

Small heat shock proteins (sHSPs) are critical for plant response to biotic and abiotic stresses, especially heat stress. They have also been implicated in various aspects of plant development. However, the acting mechanisms of the sHSPs in plants, especially in perennial grass species, remain largely elusive.

RESULTS

In this study, AsHSP26.8a, a novel chloroplast-localized sHSP gene from creeping bentgrass (Agrostis stolonifera L.) was cloned and its role in plant response to environmental stress was studied. AsHSP26.8a encodes a protein of 26.8 kDa. Its expression was strongly induced in both leaf and root tissues by heat stress. Transgenic Arabidopsis plants overexpressing AsHSP26.8a displayed reduced tolerance to heat stress. Furthermore, overexpression of AsHSP26.8a resulted in hypersensitivity to hormone ABA and salinity stress. Global gene expression analysis revealed AsHSP26.8a-modulated expression of heat-shock transcription factor gene, and the involvement of AsHSP26.8a in ABA-dependent and -independent as well as other stress signaling pathways.

CONCLUSIONS

Our results suggest that AsHSP26.8a may negatively regulate plant response to various abiotic stresses through modulating ABA and other stress signaling pathways.

Plasma Membrane Ca2+ Permeable Mechanosensitive Channel OsDMT1 Is Involved in Regulation of Plant Architecture and Ion Homeostasis in Rice

Plant architecture is an important factor for crop production. Plant height, tiller pattern, and panicle morphology are decisive factors for high grain yield in rice. Here, we isolated and characterized a T-DNA insertion rice mutant Osdmt1 (Oryza sativa dwarf and multi-tillering1) that exhibited a severe dwarf phenotype and multi-tillering. Molecular cloning revealed that DMT1 encodes a plasma membrane protein that was identified as a putative Ca²⁺ permeable mechanosensitive channel. The transcript expression level was significantly higher in the dmt1 mutant compared to wild type (WT). Additionally, the dmt1 homozygous mutant displayed a stronger phenotype than that of the WT and heterozygous seedlings after gibberellic acid (GA) treatment. RNA-seq and iTRAQ-based proteome analyses were performed between the dmt1 mutant and WT. The transcriptome profile revealed that several genes involved in GA and strigolactone (SL) biosyntheses were altered in the dmt1 mutant. Ca²⁺ and other ion concentrations were significantly enhanced in the dmt1 mutant, suggesting that DMT1 contributes to the accumulation of several ions in rice. Moreover, several EF-hand Ca²⁺ sensors, including CMLs (CaM-like proteins) and CDPKs (calcium-dependent protein kinases), displayed markedly altered transcript expression and protein levels in the dmt1 mutant. Overall, these findings aid in the elucidation of the multiply regulatory roles of OsDMT1/OsMCA1 in rice.

Isolation and expression analysis of CsCML genes in response to abiotic stresses in the tea plant (Camellia sinensis)

Calmodulin-like (CML) proteins are a class of important Ca2+ sensors in plants, which play vital roles in regulating plant growth and development and response to abiotic stress. Tea plant (Camellia sinensis L.) is the most popular non-alcoholic economic beverage crop around the world. However, the potential functions of CMLs in either tea plants growth or in the response to environmental stresses are still unclear. In the present study, five CsCML genes (CsCML16, CsCML18-1, CsCML18-2, CsCML38, and CsCML42) were isolated from tea plant, and functionally characterized. The CsCML genes showed diverse expression patterns in leaves, roots, old stems, immature stems and flowers of tea plants. To investigate the expression changes of the genes under various abiotic stresses and ABA treatment, time-course experiments were also performed, the results indicated that the expression levels of CsCML16, 18-2 and 42 were significantly induced under low temperature and salt condition, while CsCML38 was induced distinctly under drought stress and ABA treatment. Overall, CsCML genes showed diverse function in tea plant under various stimuli. These results will increase our knowledge of the significance of CsCML genes in tea plant in response to abiotic stresses and hormone treatments.

A systematic screen of conserved Ralstonia solanacearum effectors reveals the role of RipAB, a nuclear-localized effector that suppresses immune responses in potato

Both Solanum tuberosum and Ralstonia solanacearum phylotype IIB originated in South America and share a long-term co-evolutionary history. However, our knowledge of potato bacterial wilt pathogenesis is scarce as a result of the technical difficulties of potato plant manipulation. Thus, we established a multiple screening system (virulence screen of effector mutants in potato, growth inhibition of yeast and transient expression in Nicotiana benthamiana) of core type III effectors (T3Es) of a major potato pathovar of phylotype IIB, to provide more research perspectives and biological tools. Using this system, we identified four effectors contributing to virulence during potato infection, with two exhibiting multiple phenotypes in two other systems, including RipAB. Further study showed that RipAB is an unknown protein with a nuclear localization signal (NLS). Furthermore, we generated a ripAB complementation strain and transgenic ripAB-expressing potato plants, and subsequent virulence assays confirmed that R. solanacearum requires RipAB for full virulence. Compared with wild-type potato, transcriptomic analysis of transgenic ripAB-expressing potato plants showed a significant down-regulation of Ca2+ signalling-related genes in the enriched Plant-Pathogen Interaction (PPI) gene ontology (GO) term. We further verified that, during infection, RipAB is required for the down-regulation of four Ca2+ sensors, Stcml5, Stcml23, Stcml-cast and Stcdpk2, and a Ca2+ transporter, Stcngc1. Further evidence showed that the immune-associated reactive oxygen species (ROS) burst is attenuated in ripAB transgenic potato plants. In conclusion, a systematic screen of conserved R. solanacearum effectors revealed an important role for RipAB, which interferes with Ca2+ -dependent gene expression to promote disease development in potato.

CaHSL1 Acts as a Positive Regulator of Pepper Thermotolerance Under High Humidity and Is Transcriptionally Modulated by CaWRKY40

Pepper (Capsicum annuum) is an economically important vegetable and heat stress can severely impair pepper growth, development, and productivity. The molecular mechanisms underlying pepper thermotolerance are therefore important to understand but remain elusive. In the present study, we characterized the function of CaHSL1, encoding a HAESA-LIKE (HSL) receptor-like protein kinase (RLK), during the response of pepper to high temperature and high humidity (HTHH). CaHSL1 exhibits the typical structural features of an arginine-aspartate RLK. Transient overexpression of CaHSL1 in the mesophyll cells of Nicotiana benthamiana showed that CaHSL1 localizes throughout the cell, including the plasma membrane, cytoplasm, and the nucleus. CaHSL1 was significantly upregulated by HTHH or the exogenous application of abscisic acid but not by R. solanacearum inoculation. However, CaHSL1 was downregulated by exogenously applied salicylic acid, methyl jasmonate, or ethephon. Silencing of CaHSL1 by virus-induced gene silencing significantly was reduced tolerance to HTHH and downregulated transcript levels of an associated gene CaHSP24. In contrast, transient overexpression of CaHSL1 enhanced the transcript abundance of CaHSP24 and increased tolerance to HTHH, as manifested by enhanced optimal/maximal photochemical efficiency of photosystem II in the dark (Fv/Fm) and actual photochemical efficiency of photosystem II in the light. In addition, CaWRKY40 targeted the promoter of CaHSL1 and induced transcription during HTHH but not in response to R. solanacearum. All of these results suggest that CaHSL1 is directly modulated at the transcriptional level by CaWRKY40 and functions as a positive regulator in the response of pepper to HTHH.

Circadian oscillations of cytosolic free calcium regulate the Arabidopsis circadian clock

In the last decade, the view of circadian oscillators has expanded from transcriptional feedback to incorporate post-transcriptional, post-translational, metabolic processes and ionic signalling. In plants and animals, there are circadian oscillations in the concentration of cytosolic free Ca2+ ([Ca2+]cyt), though their purpose has not been fully characterized. We investigated whether circadian oscillations of [Ca2+]cyt regulate the circadian oscillator of Arabidopsis thaliana. We report that in Arabidopsis, [Ca2+]cyt circadian oscillations can regulate circadian clock function through the Ca2+-dependent action of CALMODULIN-LIKE24 (CML24). Genetic analyses demonstrate a linkage between CML24 and the circadian oscillator, through pathways involving the circadian oscillator gene TIMING OF CAB2 EXPRESSION1 (TOC1).

A mongolian pine specific endoplasmic reticulum localized CALMODULIN-LIKE calcium binding protein enhances arabidopsis growth

Stress-adapted wild plants are natural sources of novel genes for molecular breeding. Here, we conducted a transcriptional analysis of Pinus sylvestris var. mongolica Litv, an evergreen pine in northeastern China, to identify a novel CALMODULIN-LIKE protein-encoding gene, PsCML1, no significant homologs found in other plant species. PsCML1 encodes a protein predicted to have a single trans-membrane domain at its N-terminal. Four EF-hand motifs (calcium [Ca]-binding structures) are located at its C-terminal and showed Ca²⁺-specific affinity in isothermal titration calorimetric analysis. Transient expression of PsCML1 in Nicotiana benthamiana showed that the PsCML1 localizes to the endoplasmic reticulum (ER). Heterologous expression of PsCML1 in Arabidopsis significantly promoted seedling growth, and increased resistance to stress from NaCl and Ca²⁺ deficiency. The roots of the transgenic seedlings had higher contents of cellulose and pectin, but less hemicellulose than those of the wild type (WT). The biosynthesis of cell wall components is linked with protein glycosylation in the ER and reactive oxygen species (ROS) homeostasis. No significant difference was found in the extent of protein glycosylation between the transgenic and WT plants. However, the transgenic roots had higher steady-state levels of ROS, NADPH oxidase activity, and endo-membrane dynamics than those of the WT. A working model was proposed to delineate the interaction among Ca²⁺, ROS homeostasis, and cell wall loosening-dependent cell division.

Arabidopsis IQM4, a Novel Calmodulin-Binding Protein, Is Involved With Seed Dormancy and Germination in Arabidopsis

Seed dormancy and germination are regulated by complex mechanisms controlled by diverse hormones and environmental cues. Abscisic acid (ABA) promotes seed dormancy and inhibits seed germination and post-germination growth. Calmodulin (CaM) signals are involved with the inhibition of ABA during seed germination and seedling growth. In this study, we showed that Arabidopsis thaliana IQM4 could bind with calmodulin 5 (CaM5) both in vitro and in vivo, and that the interaction was the Ca2+-independent type. The IQM4 protein was localized in the chloroplast and the IQM4 gene was expressed in most tissues, especially the embryo and germinated seedlings. The T-DNA insertion mutants of IQM4 exhibited the reduced primary seed dormancy and lower ABA levels compared with wild type seeds. Moreover, IQM4 plays key roles in modulating the responses to ABA, salt, and osmotic stress during seed germination and post-germination growth. T-DNA insertion mutants exhibited ABA-insensitive and salt-hypersensitive phenotypes during seed germination and post-germination growth, whereas IQM4-overexpressing lines had ABA- and osmotic-hypersensitive, and salt-insensitive phenotypes. Gene expression analyses showed that mutation of IQM4 inhibited the expression of ABA biosynthetic genes NCED6 and NCED9, and seed maturation regulators LEC1, LEC2, ABI3, and ABI5 during the silique development, as well as promoted the expression of WRKY40 and inhibited that of ABI5 in ABA-regulated seed germination. These observations suggest that IQM4 is a novel Ca2+-independent CaM-binding protein, which is positively involved with seed dormancy and germination in Arabidopsis.

Herbivory-responsive calmodulin-like protein CML9 does not guide jasmonate-mediated defenses in Arabidopsis thaliana

Calcium is an important second messenger in plants that is released into the cytosol early after recognition of various environmental stimuli. Decoding of such calcium signals by calcium sensors is the key for the plant to react appropriately to each stimulus. Several members of Calmodulin-like proteins (CMLs) act as calcium sensors and some are known to mediate both abiotic and biotic stress responses. Here, we study the role of the Arabidopsis thaliana CML9 in different stress responses. CML9 was reported earlier as defense regulator against Pseudomonas syringae. In contrast to salicylic acid-mediated defense against biotrophic pathogens such as P. syringae, defenses against herbivores and necrotrophic fungi are mediated by jasmonates. We demonstrate that CML9 is induced upon wounding and feeding of the insect herbivore Spodoptera littoralis. However, neither different CML9 loss-of-function mutant lines nor overexpression lines were impaired upon insect feeding. No difference in herbivore-induced phytohormone elevation was detected in cml9 lines. The defense against the spider mite Tetranychus urticae was also unaffected. In addition, cml9 mutant lines showed a wild type-like reaction to the necrotrophic fungus Alternaria brassicicola. Thus, our data suggest that CML9 might be a regulator involved only in the defense against biotrophic pathogens, independent of jasmonates. In addition, our data challenge the involvement of CML9 in plant drought stress response. Taken together, we suggest that CML9 is a specialized rather than a general regulator of stress responses in Arabidopsis.

Towards Understanding Plant Calcium Signaling through Calmodulin-Like Proteins: A Biochemical and Structural Perspective

Ca2+ ions play a key role in a wide variety of environmental responses and developmental processes in plants, and several protein families with Ca2+-binding domains have evolved to meet these needs, including calmodulin (CaM) and calmodulin-like proteins (CMLs). These proteins have no catalytic activity, but rather act as sensor relays that regulate downstream targets. While CaM is well-studied, CMLs remain poorly characterized at both the structural and functional levels, even if they are the largest class of Ca2+ sensors in plants. The major structural theme in CMLs consists of EF-hands, and variations in these domains are predicted to significantly contribute to the functional versatility of CMLs. Herein, we focus on recent advances in understanding the features of CMLs from biochemical and structural points of view. The analysis of the metal binding and structural properties of CMLs can provide valuable insight into how such a vast array of CML proteins can coexist, with no apparent functional redundancy, and how these proteins contribute to cellular signaling while maintaining properties that are distinct from CaM and other Ca2+ sensors. An overview of the principal techniques used to study the biochemical properties of these interesting Ca2+ sensors is also presented.

Advances and current challenges in calcium signaling

Content Summary 414 I. Introduction 415 II. Ca²⁺ importer and exporter in plants 415 III. The Ca²⁺ decoding toolkit in plants 415 IV. Mechanisms of Ca²⁺ signal decoding 417 V. Immediate Ca²⁺ signaling in the regulation of ion transport 418 VI. Ca²⁺ signal integration into long-term ABA responses 419 VII Integration of Ca²⁺ and hormone signaling through dynamic complex modulation of the CCaMK/CYCLOPS complex 420 VIII Ca²⁺ signaling in mitochondria and chloroplasts 422 IX A view beyond recent advances in Ca²⁺ imaging 423 X Modeling approaches in Ca²⁺ signaling 424 XI Conclusions: Ca²⁺ signaling a still young blooming field of plant research 424 Acknowledgements 425 ORCID 425 References 425 SUMMARY: Temporally and spatially defined changes in Ca²⁺ concentration in distinct compartments of cells represent a universal information code in plants. Recently, it has become evident that Ca²⁺ signals not only govern intracellular regulation but also appear to contribute to long distance or even organismic signal propagation and physiological response regulation. Ca²⁺ signals are shaped by an intimate interplay of channels and transporters, and during past years important contributing individual components have been identified and characterized. Ca²⁺ signals are translated by an elaborate toolkit of Ca²⁺ -binding proteins, many of which function as Ca²⁺ sensors, into defined downstream responses. Intriguing progress has been achieved in identifying specific modules that interconnect Ca²⁺ decoding proteins and protein kinases with downstream target effectors, and in characterizing molecular details of these processes. In this review, we reflect on recent major advances in our understanding of Ca²⁺ signaling and cover emerging concepts and existing open questions that should be informative also for scientists that are currently entering this field of ever-increasing breath and impact.