Evidence for the possible involvement of calmodulin in regulation of steady state levels of Hsp90 family members (Hsp87 and Hsp85) in response to heat shock in sorghum

Calmodulin, Calcium/Calmodulin-Dependent Kinases-1 and 2 Regulate Expression of the Heat Shock Proteins for Heat Shock Tolerance and Pheromone Signaling Genes for Sexual Development in Neurospora crassa

Calmodulin (CaM) is a primary Ca2+ sensor that binds and activates numerous target proteins and regulates several cellular processes in eukaryotes. CaM is essential in Neurospora crassa; therefore, we generated a CaM mutant using repeat-induced point (RIP) mutation and investigated the cmdRIP mutant phenotypes. We also studied knockout mutants of four Ca2+/CaM kinases (camk-1, 2, 3, and 4) for their role during stress conditions and sexual development. The cmdRIP, ∆camk-1, and ∆camk-2 mutants showed reduced survival and growth rates under heat stress, oxidative stress, pH, and ER stress conditions. In addition, under the heat stress conditions, expression of the heat shock protein genes hsp70 and hsp80 was reduced in the cmdRIP, ∆camk-1, and ∆camk-2 mutants. The cmdRIP mutant was also defective in cell fusion, its vegetative hyphae could not support the fertilized wild type perithecia graft, and female sterile. Furthermore, the expression of pheromone signaling genes pre-1, pre-2, ccg-4, mfa-1, and fmf-1 was reduced in the cmdRIP, ∆camk-1, and ∆camk-2 mutants. Therefore, CaM, Ca2+/CaMK-1 and 2 are involved in the tolerance to heat stress conditions and sexual development by regulating the heat shock and pheromone response pathways, respectively, in N. crassa.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01091-8.

Generation of GCaMP6s-Expressing Zebrafish to Monitor Spatiotemporal Dynamics of Calcium Signaling Elicited by Heat Stress

The ability of organisms to quickly sense and transduce signals of environmental stresses is critical for their survival. Ca²⁺ is a versatile intracellular messenger involved in sensing a wide variety of stresses and regulating the subsequent cellular responses. So far, our understanding for calcium signaling was mostly obtained from ex vivo tissues and cultured cell lines, and the in vivo spatiotemporal dynamics of stress-triggered calcium signaling in a vertebrate remains to be characterized. Here, we describe the generation and characterization of a transgenic zebrafish line with ubiquitous expression of GCaMP6s, a genetically encoded calcium indicator (GECI). We developed a method to investigate the spatiotemporal patterns of Ca²⁺ events induced by heat stress. Exposure to heat stress elicited immediate and transient calcium signaling in developing zebrafish. Cells extensively distributed in the integument of the head and body trunk were the first batch of responders and different cell populations demonstrated distinct response patterns upon heat stress. Activity of the heat stress-induced calcium signaling peaked at 30 s and swiftly decreased to near the basal level at 120 s after the beginning of exposure. Inhibition of the heat-induced calcium signaling by LaCl₃ and capsazepine and treatment with the inhibitors for CaMKII (Ca²²/calmodulin-dependent protein kinase II) and HSF1 (Heat shock factor 1) all significantly depressed the enhanced heat shock response (HSR). Together, we delineated the spatiotemporal dynamics of heat-induced calcium signaling and confirmed functions of the Ca²⁺-CaMKII-HSF1 pathway in regulating the HSR in zebrafish.

Overexpression of CsCaM3 Improves High Temperature Tolerance in Cucumber

High temperature (HT) stress affects the growth and production of cucumbers, but genetic resources with high heat tolerance are very scarce in this crop. Calmodulin (CaM) has been confirmed to be related to the regulation of HT stress resistance in plants. CsCaM3, a CaM gene, was isolated from cucumber inbred line "02-8." Its expression was characterized in the present study. CsCaM3 transcripts differed among the organs and tissues of cucumber plants and could be induced by HTs or abscisic acid, but not by salicylic acid. CsCaM3 transcripts exhibited subcellular localization to the cytoplasm and nuclei of cells. Overexpression of CsCaM3 in cucumber plants has the potential to improve their heat tolerance and protect against oxidative damage and photosynthesis system damage by regulating the expression of HT-responsive genes in plants, including chlorophyll catabolism-related genes under HT stress. Taken together, our results provide useful insights into stress tolerance in cucumber.

A temperature-responsive gene in sorghum encodes a glycine-rich protein that interacts with calmodulin

Imposition of different biotic and abiotic stress conditions results in an increase in intracellular levels of Ca²⁺ which is sensed by various sensor proteins. Calmodulin (CaM) is one of the best studied transducers of Ca²⁺ signals. CaM undergoes conformational changes upon binding to Ca²⁺ and interacts with different types of proteins, thereby, regulating their activities. The present study reports the cloning and characterization of a sorghum cDNA encoding a protein (SbGRBP) that shows homology to glycine-rich RNA-binding proteins. The expression of SbGRBP in the sorghum seedlings is modulated by heat stress. The SbGRBP protein is localized in the nucleus as well as in cytosol, and shows interaction with CaM that requires the presence of Ca²⁺. SbGRBP depicts binding to single- and also double-stranded DNA. Fluorescence spectroscopic analyses suggest that interaction of SbGRBP with nucleic acids may be modulated after binding with CaM. To our knowledge, this is the first study to provide evidence for interaction of a stress regulated glycine-rich RNA-binding protein with CaM.

Characterization and Expression Profiling Analysis of Calmodulin Genes in Response to Salt and Osmotic Stresses in Pear (Pyrus bretschneideri Rehd.) and in Comparison with Arabidopsis

A genome-wide identification and cloning of CaM genes in pear was conducted and in compared with Arabidopsis that indicated a conserved expansion of CaM genes in pear, and PbCaMs and AtCaMs had a similar distribution of cis-elements and expressions in response to salt and osmotic stress. In particular, PbCaM1 and PbCaM3 were both significantly upregulated in response to salt and osmotic stress in pear.

Abiotic stress responses in plants: roles of calmodulin-regulated proteins

Intracellular changes in calcium ions (Ca(2+)) in response to different biotic and abiotic stimuli are detected by various sensor proteins in the plant cell. Calmodulin (CaM) is one of the most extensively studied Ca(2+)-sensing proteins and has been shown to be involved in transduction of Ca(2+) signals. After interacting with Ca(2+), CaM undergoes conformational change and influences the activities of a diverse range of CaM-binding proteins. A number of CaM-binding proteins have also been implicated in stress responses in plants, highlighting the central role played by CaM in adaptation to adverse environmental conditions. Stress adaptation in plants is a highly complex and multigenic response. Identification and characterization of CaM-modulated proteins in relation to different abiotic stresses could, therefore, prove to be essential for a deeper understanding of the molecular mechanisms involved in abiotic stress tolerance in plants. Various studies have revealed involvement of CaM in regulation of metal ions uptake, generation of reactive oxygen species and modulation of transcription factors such as CAMTA3, GTL1, and WRKY39. Activities of several kinases and phosphatases have also been shown to be modulated by CaM, thus providing further versatility to stress-associated signal transduction pathways. The results obtained from contemporary studies are consistent with the proposed role of CaM as an integrator of different stress signaling pathways, which allows plants to maintain homeostasis between different cellular processes. In this review, we have attempted to present the current state of understanding of the role of CaM in modulating different stress-regulated proteins and its implications in augmenting abiotic stress tolerance in plants.

Characterization of Peptidyl-Prolyl Cis-Trans Isomerase- and Calmodulin-Binding Activity of a Cytosolic Arabidopsis thaliana Cyclophilin AtCyp19-3

Cyclophilins, which bind to immunosuppressant cyclosporin A (CsA), are ubiquitous proteins and constitute a multigene family in higher organisms. Several members of this family are reported to catalyze cis-trans isomerisation of the peptidyl-prolyl bond, which is a rate limiting step in protein folding. The physiological role of these proteins in plants, with few exceptions, is still a matter of speculation. Although Arabidopsis genome is predicted to contain 35 cyclophilin genes, biochemical characterization, imperative for understanding their cellular function(s), has been carried only for few of the members. The present study reports the biochemical characterization of an Arabidopsis cyclophilin, AtCyp19-3, which demonstrated that this protein is enzymatically active and possesses peptidyl-prolyl cis-trans isomerase (PPIase) activity that is specifically inhibited by CsA with an inhibition constant (Ki) of 18.75 nM. The PPIase activity of AtCyp19-3 was also sensitive to Cu(2+), which covalently reacts with the sulfhydryl groups, implying redox regulation. Further, using calmodulin (CaM) gel overlay assays it was demonstrated that in vitro interaction of AtCyp19-3 with CaM is Ca(2+)-dependent, and CaM-binding domain is localized to 35-70 amino acid residues in the N-terminus. Bimolecular fluorescence complementation assays showed that AtCyp19-3 interacts with CaM in vivo also, thus, validating the in vitro observations. However, the PPIase activity of the Arabidopsis cyclophilin was not affected by CaM. The implications of these findings are discussed in the context of Ca(2+) signaling and cyclophilin activity in Arabidopsis.

Reference gene selection for qPCR in Ammopiptanthus mongolicus under abiotic stresses and expression analysis of seven ROS-scavenging enzyme genes

Ammopiptanthus mongolicus, the only evergreen broadleaf shrub endemic to the northwest desert of China, is a valuable species for plant abiotic stress research. No report has so far described the selection of reference genes to get stringent normalization for qPCR in A. mongolicus. This work identified reliable reference genes for normalization of qPCR data in A. mongolicus under abiotic stresses from 14 reference gene candidates (UBQ, Tub1, Tub2, Abc1, Ubc1, Ubc2, Ubc4, Ubc5, eIF1, eIF2, eIF3, eIF4, EF1, EF2), and used the most suitable combination of reference genes to normalize the expression profiles of seven ROS-scavenging enzyme genes (AmSOD, AmAPX, AmGPX, AmCAT, AmGLR, AmPrx, and AmTrx). We set a series of 22 experimental samples covering the control and different time points under cold, dry, salt, and heat stresses. According to geNorm and NormFinder, the combination of eIF1 and eIF3 was best for accurate normalization across all the treatments, confirmed by normalizing qPCR data with AmHsp90. In contrast, these data show that Tub1, Abc1, and EF1 are not suitable reference gene candidates. After being normalized against eIF1 and eIF3, the seven ROS-scavenging enzyme genes exhibited differentially up- or down-regulated expression patterns. AmSOD and AmGPX were up-regulated by all four treatments, indicating that they may participate in an anti-oxidative mechanism under abiotic stresses in A. mongolicus. AmCAT exhibited a much higher expression level than AmAPX, AmPrx, and AmGPX, suggesting a principle role in detoxifying excessive H₂O₂. AmSOD, AmGPX and AmAPX showing the most abundant transcripts under heat, AmCAT and AmGLR under drought, and AmPrx under salt, were observed. Expression patterns of the seven ROS-scavenging enzyme genes suggest different antioxidant protection roles of these genes under abiotic stresses. These results are valuable for future research on gene expression and abiotic stress tolerance in A. mongolicus.