Calcium/calmodulin-mediated microbial symbiotic interactions in plants.

Cytoplasmic calcium (Ca) transients and nuclear Ca oscillations act as hubs during root nodulation and arbuscular mycorrhizal symbioses. Plants perceive bacterial Nod factors or fungal signals to induce the Ca oscillation in the nucleus of root hair cells, and subsequently activate calmodulin (CaM) and Ca/CaM-dependent protein kinase (CCaMK). Ca and CaM-bound CCaMK phosphorylate transcription factors then initiate down-stream signaling events.

Calcium/Calmodulin-Mediated Defense Signaling: What Is Looming on the Horizon for AtSR1/CAMTA3-Mediated Signaling in Plant Immunity.

Calcium (Ca) signaling in plant cells is an essential and early event during plant-microbe interactions. The recognition of microbe-derived molecules activates Ca channels or Ca pumps that trigger a transient increase in Ca in the cytoplasm. The Ca binding proteins (such as CBL, CPK, CaM, and CML), known as Ca sensors, relay the Ca signal into down-stream signaling events, e.

Calmodulin-binding transcription activator AtSR1/CAMTA3 fine-tunes plant immune response by transcriptional regulation of the salicylate receptor NPR1.

Calcium (Ca ) signalling regulates salicylic acid (SA)-mediated immune response through calmodulin-meditated transcriptional activators, AtSRs/CAMTAs, but its mechanism is not fully understood. Here, we report an AtSR1/CAMTA3-mediated regulatory mechanism involving the expression of the SA receptor, NPR1. Results indicate that the transcriptional expression of NPR1 was regulated by AtSR1 binding to a CGCG box in the NPR1 promotor.

Distinct Molecular Pattern-Induced Calcium Signatures Lead to Different Downstream Transcriptional Regulations via AtSR1/CAMTA3.

Plants encrypt the perception of different pathogenic stimuli into specific intracellular calcium (Ca) signatures and subsequently decrypt the signatures into appropriate downstream responses through various Ca sensors. Two microbe-associated molecular patterns (MAMPs), bacterial flg22 and fungal chitin, and one damage-associated molecular pattern (DAMP), AtPep1, were used to study the differential Ca signatures in leaves. The results revealed that flg22, chitin, and AtPep1 induced distinct changes in Ca dynamics in both the cytosol and nucleus.

Enhanced Salt Tolerance of Rhizobia-inoculated Soybean Correlates with Decreased Phosphorylation of the Transcription Factor GmMYB183 and Altered Flavonoid Biosynthesis.

Soybean ( (L.) Merrill) is an important component of the human diet and animal feed, but soybean production is limited by abiotic stresses especially salinity. We recently found that rhizobia inoculation enhances soybean tolerance to salt stress, but the underlying mechanisms are unaddressed.

A Ca/CaM-regulated transcriptional switch modulates stomatal development in response to water deficit.

Calcium (Ca) signals are decoded by the Ca-sensor protein calmodulin (CaM) and are transduced to Ca/CaM-binding transcription factors to directly regulate gene expression necessary for acclimation responses in plants. The molecular mechanisms of Ca/CaM signal transduction processes and their functional significance remains enigmatic. Here we report a novel Ca/CaM signal transduction mechanism that allosterically regulates DNA-binding activity of GT2-LIKE 1 (GTL1), a transrepressor of STOMATAL DENSITY AND DISTRIBUTION 1 (SDD1), to repress stomatal development in response to water stress.

Mutual interplay of Ca and ROS signaling in plant immune response.

Second messengers are cellular chemicals that act as "language codes", allowing cells to pass outside information to the cell interior. The cells then respond through triggering downstream reactions, including transcriptional reprograming to affect appropriate adaptive responses. The spatiotemporal patterning of these stimuli-induced signal changes has been referred to as a "signature", which is detected, decoded, and transmitted to elicit these downstream cellular responses.

Calcium Signaling-Mediated Plant Response to Cold Stress.

Low temperatures have adverse impacts on plant growth, developmental processes, crop productivity and food quality. It is becoming clear that Ca signaling plays a crucial role in conferring cold tolerance in plants. However, the role of Ca involved in cold stress response needs to be further elucidated.

Ca/Calmodulin-Dependent AtSR1/CAMTA3 Plays Critical Roles in Balancing Plant Growth and Immunity.

During plant-pathogen interactions, plants have to relocate their resources including energy to defend invading organisms; as a result, plant growth and development are usually reduced. signal responsive1 (AtSR1) has been documented as a negative regulator of plant immune responses and could serve as a positive regulator of plant growth and development. However, the mechanism by which AtSR1 balances plant growth and immunity is poorly understood.

Quantitative Phosphoproteomic and Metabolomic Analyses Reveal GmMYB173 Optimizes Flavonoid Metabolism in Soybean under Salt Stress.

Salinity causes osmotic stress to crops and limits their productivity. To understand the mechanism underlying soybean salt tolerance, proteomics approach was used to identify phosphoproteins altered by NaCl treatment. Results revealed that 412 of the 4698 quantitatively analyzed phosphopeptides were significantly up-regulated on salt treatment, including a phosphopeptide covering the serine 59 in the transcription factor GmMYB173.

W342F Mutation in CCaMK Enhances Its Affinity to Calmodulin But Compromises Its Role in Supporting Root Nodule Symbiosis in .

The calcium/calmodulin-dependent protein kinase (CCaMK) is regulated by free Ca and Ca-loaded calmodulin. This dual binding is believed to be involved in its regulation and associated physiological functions, although direct experimental evidence for this is lacking. Here we document that site-directed mutations in the calmodulin-binding domain of CCaMK alters its binding capacity to calmodulin, providing an effective approach to study how calmodulin regulates CCaMK in terms of kinase activity and regulation of rhizobial symbiosis in .

Autophosphorylation of calcium/calmodulin-dependent protein kinase (CCaMK) at S343 or S344 generates an intramolecular interaction blocking the CaM-binding.

The Ca and Ca/calmodulin-dependent protein kinase (CCaMK) is an important effector protein of Ca/calmodulin-mediated signaling, and in legumes, it is a critical regulator of plant-rhizobia and mycorrhizal symbioses. CCaMK contains a kinase domain, a calmodulin-binding/autoinhibitory domain and a visinin-like domain. Previous studies revealed the presence of 2 phosphorylation sites, S343 and S344, in the calmodulin-binding domain.

Calcium signatures and signaling events orchestrate plant-microbe interactions.

Calcium (Ca) acts as an essential second messenger connecting the perception of microbe signals to the establishment of appropriate immune and symbiotic responses in plants. Accumulating evidence suggests that plants distinguish different microorganisms through plasma membrane-localized pattern recognition receptors. The particular recognition events are encoded into Ca signatures, which are sensed by diverse intracellular Ca binding proteins.

Involvement of calmodulin and calmodulin-like proteins in plant responses to abiotic stresses.

Transient changes in intracellular Ca(2+) concentration have been well recognized to act as cell signals coupling various environmental stimuli to appropriate physiological responses with accuracy and specificity in plants. Calmodulin (CaM) and calmodulin-like proteins (CMLs) are major Ca(2+) sensors, playing critical roles in interpreting encrypted Ca(2+) signals. Ca(2+)-loaded CaM/CMLs interact and regulate a broad spectrum of target proteins such as channels/pumps/antiporters for various ions, transcription factors, protein kinases, protein phosphatases, metabolic enzymes, and proteins with unknown biochemical functions.

Calcium signaling and biotic defense responses in plants.

Calcium (Ca(2+)) acts as an important second messenger in plant cells. Cytosolic free Ca(2+) concentration in plant cells changes rapidly and dynamically in response to various endogenous or environmental cues. Elevation in calcium concentration in plant cells is an essential early event during plant defense responses.

Regulation of plant immunity through ubiquitin-mediated modulation of Ca(2+) -calmodulin-AtSR1/CAMTA3 signaling.

Transient changes in intracellular Ca(2+) concentration are essential signals for activation of plant immunity. It has also been reported that Ca(2+) signals suppress salicylic acid-mediated plant defense through AtSR1/CAMTA3, a member of the Ca(2+) /calmodulin-regulated transcription factor family that is conserved in multicellular eukaryotes. How plants overcome this negative regulation to mount an effective defense response during a stage of intracellular Ca(2+) surge is unclear.

Recent advances in calcium/calmodulin-mediated signaling with an emphasis on plant-microbe interactions.

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Phosphorylation of S344 in the calmodulin-binding domain negatively affects CCaMK function during bacterial and fungal symbioses.

Calcium and Ca(2+)/calmodulin-dependent protein kinase (CCaMK) plays a critical role in the signaling pathway that establishes root nodule symbiosis and arbuscular mycorrhizal symbiosis. Calcium-dependent autophosphorylation is central to the regulation of CCaMK, and this has been shown to promote calmodulin binding. Here, we report a regulatory mechanism of Medicago truncatula CCaMK (MtCCaMK) through autophosphorylation of S344 in the calmodulin-binding/autoinhibitory domain.

The function of calreticulin in plant immunity: new discoveries for an old protein.

Since its initial discovery as a high affinity Ca ( 2+) -binding protein in the sarcoplasmic reticulum and endoplasmic reticulum (ER), calreticulin (CRT) has been documented to be a multifunctional protein in both animal and plant cells. This protein is well recognized as a Ca ( 2+) -binding molecular chaperone that facilitates the folding of newly synthesized glycoproteins and regulates the Ca ( 2+) homeostasis in the ER lumen. However, functional relevance associated with its localization in other cellular compartments has also been reported.

Coupling calcium/calmodulin-mediated signaling and herbivore-induced plant response through calmodulin-binding transcription factor AtSR1/CAMTA3.

Calcium/calmodulin (Ca(2+)/CaM) has long been considered a crucial component in wound signaling pathway. However, very few Ca(2+)/CaM-binding proteins have been identified which regulate plant responses to herbivore attack/wounding stress. We have reported earlier that a family of Ca(2+)/CaM-binding transcription factors designated as AtSRs (also known as AtCAMTAs) can respond differentially to wounding stress.

Plant-specific trihelix transcription factor AtGT2L interacts with calcium/calmodulin and responds to cold and salt stresses.

GT factors are a family of plant-specific transcription factors with conserved trihelix DNA-binding domains that bind GT elements. By screening a cDNA expression library with (35)S-labeled recombinant calmodulin (CaM), we identified AtGT2L, a classic member of GT-2 subfamily, as a Ca(2+)-dependent CaM-binding protein. AtGT2L specifically targets the nucleus and possesses both transcriptional activation and DNA-binding abilities, implicating its function as a nuclear transcription factor.

A dual regulatory role of Arabidopsis calreticulin-2 in plant innate immunity.

Calreticulin (CRT) is an endoplasmic reticulum-resident calcium-binding molecular chaperone that is highly conserved in multi-cellular eukaryotes. Higher plants contain two distinct groups of CRTs: CRT1/CRT2 and CRT3 isoforms. Previous studies have shown that bacterial elongation factor Tu receptor (EFR), a pattern-recognition receptor that is responsible for pathogen-associated molecular pattern-triggered immunity, is a substrate for Arabidopsis CRT3, suggesting a role for CRT3 in regulating plant defense against pathogens.