StCaM2, a calcium binding protein, alleviates negative effects of salinity and drought stress in tobacco

β-Cyclocitric acid enhances drought tolerance in peach (Prunus persica) seedlings

The β-cyclocitric acid (β-CCA) is a bioactive apocarotenoid previously shown to improve drought tolerance in annual plants. However, the underlying molecular mechanism of this process remains largely elusive. Moreover, the question about the activity of β-CCA in perennial fruit crops is still open. Here, we found that treatment of β-CCA enhances drought tolerance in peach seedlings. The application of β-CCA significantly increased the relative water content and root activity and reduced the electrolyte leakage of peach seedlings under drought stress. Moreover, treatment with β-CCA under drought stress increased chlorophyll fluorescence, indicating a positive effect on photosynthesis, while also enhancing superoxide dismutase and peroxidase activity and reducing reactive oxygen species (ROS) levels. Consistent with these alterations, transcriptome analysis revealed an up-regulation of photosynthesis and antioxidant-related genes upon the application of β-CCA under drought stress. We also detected an induction in genes related to detoxification, environmental adaptation, primary metabolism, phytohormone, phenylpropanoid and the biosynthesis of cutin, suberine and wax, which might contribute to the induction of drought resistance. Altogether, our study reveals that β-CCA positively modulates peach drought tolerance, which is mainly mediated by enhancing photosynthesis and reducing ROS, indicating the potential of utilizing β-CCA for drought control in peach and perhaps other fruit crops.

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.

A Review of Potato Salt Tolerance

Potato is the world's fourth largest food crop. Due to limited arable land and an ever-increasing demand for food from a growing population, it is critical to increase crop yields on existing acreage. Soil salinization is an increasing problem that dramatically impacts crop yields and restricts the growing area of potato. One possible solution to this problem is the development of salt-tolerant transgenic potato cultivars. In this work, we review the current potato planting distribution and the ways in which it overlaps with salinized land, in addition to covering the development and utilization of potato salt-tolerant cultivars. We also provide an overview of the current progress toward identifying potato salt tolerance genes and how they may be deployed to overcome the current challenges facing potato growers.

Identification and functional analysis of calcium sensor calmodulins from heavy metal hyperaccumulator Noccaea caerulescens

Noccaea caerulescens (J. Presl & C. Presl) F. K. Mey. is a heavy metal hyperaccumulator exhibiting extreme tolerance to various environmental stresses. To date, the functional role of Ca2+ -binding protein in this plant is largely unknown. To investigate the function of calmodulins (CaMs) in N. caerulescens , CaM2 , a Ca2+ sensor encoding gene, was identified and functionally characterised. Protein structure analysis showed that NcCaM2 contains four classic exchange factor (EF)-hand motifs with high sequence similarity to the CaM proteins from model plant Arabidopsis thaliana L. Tissue specific expression analysis showed that NcCaM2 is constitutively expressed in stems, leaves, and roots. Expression level of NcCaM2 was significantly upregulated under various environmental stimulus, indicating a potential involvement of NcCaM2 in the tolerance to abiotic stresses. The heterologous expression of NcCaM2 in a yeast mutant strain increased the heavy metal tolerance in yeast cells. Furthermore, the constitutive expression of NcCaM2 enhanced the heavy metal tolerance capability of transgenic tobacco (Nicotiana tabacum L.) plants. Our data suggested an important role of NcCaM2 in the responses to environmental stresses and provided a potential target gene to enhance of the ability to hyperaccumulate metals.

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.

Arabidopsis CAMTA3/SR1 is involved in drought stress tolerance and ABA signaling

Calcium/calmodulin signals are important for various cellular and physiological activities in plants. Calmodulin binding transcription activators also named Signal Responsive (SR) proteins belong to an important calcium/calmodulin-dependent transcription factor family that plays critical roles in stress responses. However, the role of SRs in abscisic acid (ABA) regulated plant responses to drought stress is largely unknown. Here, we characterized the role of Arabidopsis SR1 in drought stress tolerance and ABA response by analyzing the phenotypes of SR1 knockout and SR1-overexpression plants. sr1 mutants which accumulate salicylic acid (SA) were found more sensitive to drought stress and showed a higher water loss rate as compared with wild-type. By contrast, SR1-overexpression lines exhibited increased drought tolerance and less water loss than wild-type. Furthermore, sr1 mutants showed reduced ABA response in seed germination, root elongation, and stomatal closure, while SR1-overexpression lines displayed more sensitive to ABA than wild-type. In addition, the drought-sensitive and ABA-insensitive phenotypes of sr1 mutants were recovered by diminishing SA accumulation via knockouts of SA synthesizer ICS1 or activator PAD4, or through expression of SA-degrading enzyme NahG. Some drought/ABA-responsive genes exhibited differentially expressed in sr1 mutants and SR1-overexpression plants. These results suggest that SR1 plays a positive role in drought stress tolerance and ABA response, and drought/ABA responses are antagonized by SA accumulation that is negatively regulated by SR1.

Pyramiding of γ-TMT and gly I transgenes in Brassica juncea enhances salinity and drought stress tolerance

We previously generated Brassica juncea lines overexpressing either glyoxalase I (gly I) or γ-tocopherol methyltransferase (γ-TMT) involved in the glyoxalase system and tocopherol biosynthesis, respectively. These transgenic plants showed tolerance to multiple abiotic stresses. As tolerance is a complex trait that can be improved by pyramiding of several characteristics in a single genotype, we generated in this study B. juncea plants coexpressing gly I and γ-TMT by crossing the previously generated stable transgenic lines. The performance of the newly generated B. juncea lines coexpressing gly I and γ-TMT was compared with that of wild-type and the single transgenic lines under non-stressed and NaCl and mannitol stress conditions. Our results show a more robust antioxidant response of B. juncea plants coexpressing gly I and γ-TMT compared to the other lines in terms of higher chlorophyll retention, relative water content, antioxidant enzyme and proline levels, and photosynthetic efficiency and lower oxidative damage. The differences in response to the stress of the different lines were reflected in their yield parameters. Overall, we demonstrate that the pyramiding of multiple genes involved in antioxidant pathways could be a viable and useful approach for achieving higher abiotic stress tolerance in crop plants.

Ectopic expression of finger millet calmodulin confers drought and salinity tolerance in Arabidopsis thaliana

Overexpression of finger millet calmodulin imparts drought and salt tolerance in plants. Drought and salinity are major environmental stresses which affect crop productivity and therefore are major hindrance in feeding growing population world-wide. Calcium (Ca²⁺) signaling plays a crucial role during the plant's response to these stress stimuli. Calmodulin (CaM), a crucial Ca²⁺sensor, is involved in transducing the signal downstream in various physiological, developmental and stress responses by modulating a plethora of target proteins. The role of CaM has been well established in the model plant Arabidopsis thaliana for regulating various developmental processes, stress signaling and ion transport. In the current study, we investigate the CaM of Eleusine coracana (common name finger millet, known especially for its drought tolerance and superior Ca²⁺ content). In-silico analysis showed that Eleusine CaM (EcCaM) has greater similarity to rice CaM as compared to Arabidopsis CaM due to the presence of highly conserved four EF-hand domains. To decipher the in-planta function of EcCaM, we have adopted the gain-of-function approach by generating the 35S::EcCaM over-expression transgenic in Arabidopsis. Overexpression of EcCaM in Arabidopsis makes the plant tolerant to polyethylene glycol (PEG) induced drought and salt stress (NaCl) as demonstrated by post-germination based phenotypic assay, ion leakage, MDA and proline estimation, ROS detection under stressed and normal conditions. Moreover, EcCaM overexpression leads to hypersensitivity toward exogenously applied ABA at the seed germination stage. These findings reveal that EcCaM mediates tolerance to drought and salinity stress. Also, our results indicate that EcCaM is involved in modulating ABA signaling. Summarizing our results, we report for the first time that EcCaM is involved in modulating plants response to stress and this information can be used for the generation of future-ready crops that can tolerate a wide range of abiotic stresses.

The CaM1-associated CCaMK-MKK1/6 cascade positively affects lateral root growth via auxin signaling under salt stress in rice

Ca2+/calmodulin (CaM)-dependent protein kinases (CCaMKs) and mitogen-activated protein kinase kinases (MAPKKs) are two types of kinases that regulate salt stress response in plants. It remains unclear, however, how they cooperatively affect lateral root growth under salt stress. Here, two conserved phosphorylation sites (S102 and T118) of OsCaM1 were identified, and found to affect the ability to bind to Ca2+in vitro and the kinase activity of OsCCaMK in vivo. OsCCaMK specifically interacted with OsMKK1/6 in a Ca2+/CaM-dependent manner. In vitro kinase and in vivo dual-luciferase assays revealed that OsCCaMK phosphorylated OsMKK6 while OsMKK1 phosphorylated OsCCaMK. Overexpression and antisense-RNA repression expression of OsCaM1-1, and CRISPR/Cas9-mediated gene editing mutations of OsMKK1, OsMKK6, and OsMKK1/6 proved that OsCaM1-1, OsMKK1, and OsMKK6 enhanced the auxin content in roots and lateral root growth under salt stress. Consistently, OsCaM1-1, OsMKK1, and OsMKK6 regulated the transcript levels of the genes of this cascade, and salt stress-related and lateral root growth-related auxin signaling under salt stress in rice roots. These findings demonstrate that the OsCaM1-associated OsCCaMK-OsMKK1/6 cascade plays a critical role in recruiting auxin signaling in rice roots. These results also provide new insight into the regulatory mechanism of the CaM-mediated phosphorylation relay cascade to auxin signaling in lateral root growth under salt stress in plants.

Phylogenetic Analysis of the Membrane Attack Complex/Perforin Domain-Containing Proteins in Gossypium and the Role of GhMACPF26 in Cotton Under Cold Stress

The membrane attack complex/perforin (MACPF) domain-containing proteins are involved in the various developmental processes and in responding to diverse abiotic stress. The function and regulatory network of the MACPF genes are rarely reported in Gossypium spp. We study the detailed identification and partial functional verification of the members of the MACPF family. Totally, 100 putative MACPF proteins containing complete MACPF domain were identified from the four cotton species. They were classified into three phylogenetic groups and underwent multifold pressure indicating that selection produced new functional differentiation. Cotton MACPF gene family members expanded mainly through the whole-genome duplication (WGD)/segmental followed by the dispersed. Expression and cis-acting elements analysis revealed that MACPFs play a role in resistance to abiotic stresses, and some selected GhMACPFs were able to respond to the PEG and cold stresses. Co-expression analysis showed that GhMACPFs might interact with valine-glutamine (VQ), WRKY, and Apetala 2 (AP2)/ethylene responsive factor (ERF) domain-containing genes under cold stress. In addition, silencing endogenous GhMACPF26 in cotton by the virus-induced gene silencing (VIGS) method indicated that GhMACPF26 negatively regulates cold tolerance. Our data provided a comprehensive phylogenetic evolutionary view of Gossypium MACPFs. The MACPFs may work together with multiple transcriptional factors and play roles in acclimation to abiotic stress, especially cold stress in cotton.