Pathogen effectors hijack calcium signaling to promote virulence.

Calcium signaling is a cornerstone of plant defense responses. In this opinion article we explore how pathogens exploit this pathway by targeting calcium sensors such as calmodulin (CaM) and calmodulin-like proteins (CMLs) with their secreted effectors. We illustrate different mechanisms by which effectors manipulate calcium homeostasis, cytoskeletal dynamics, metabolism, hormone biosynthesis, gene regulation, and chloroplast function to suppress plant immunity and enhance virulence.

Calmodulin-like protein CML15 interacts with PP2C46/65 to regulate papaya fruit ripening via integrating calcium, ABA and ethylene signals.

It is well known that calcium, ethylene and abscisic acid (ABA) can regulate fruit ripening, however, their interaction in the regulation of fruit ripening has not yet been fully clarified. The present study found that the expression of the papaya calcium sensor CpCML15 was strongly linked to fruit ripening. CpCML15 could bind Ca and served as a true calcium sensor.

The Same against Many: AtCML8, a Ca Sensor Acting as a Positive Regulator of Defense Responses against Several Plant Pathogens.

Calcium signals are crucial for the activation and coordination of signaling cascades leading to the establishment of plant defense mechanisms. Here, we studied the contribution of CML8, an Arabidopsis calmodulin-like protein in response to and to pathogens with different lifestyles, such as pv. and .

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.

Specific TCP transcription factors interact with and stabilize PRR2 within different nuclear sub-domains.

Plants possess a large set of transcription factors both involved in the control of plant development or in plant stress responses coordination. We previously identified PRR2, a Pseudo-Response Regulator, as a plant-specific CML-interacting partner. We reported that PRR2 acts as a positive actor of plant defense by regulating the production of antimicrobial compounds.

Calcium Signalling in Plant Biotic Interactions.

Calcium (Ca) is a universal second messenger involved in various cellular processes, leading to plant development and to biotic and abiotic stress responses. Intracellular variation in free Ca concentration is among the earliest events following the plant perception of environmental change. These Ca variations differ in their spatio-temporal properties according to the nature, strength and duration of the stimulus.

PRR2, a pseudo-response regulator, promotes salicylic acid and camalexin accumulation during plant immunity.

Calcium signalling mediated by Calmodulin (CaM) and calmodulin-like (CML) proteins is critical to plant immunity. CaM and CML regulate a wide range of target proteins and cellular responses. While many CaM-binding proteins have been identified, few have been characterized for their specific role in plant immunity.

Respective contribution of CML8 and CML9, two arabidopsis calmodulin-like proteins, to plant stress responses.

In their natural environment, plants have to continuously face constraints such as biotic and abiotic stresses. To achieve their life cycle, plants have to perceive and interpret the nature, but also the strength of environmental stimuli to activate appropriate physiological responses. Nowadays, it is well established that signaling pathways are crucial steps in the implementation of rapid and efficient plant responses such as genetic reprogramming.

Regulation of the wheat MAP kinase phosphatase 1 by 14-3-3 proteins.

Plant MAP kinase phosphatases (MKPs) are major regulators of MAPK signaling pathways and play crucial roles in controlling growth, development and stress responses. The presence of several functional domains in plant MKPs such as a dual specificity phosphatase catalytic domain, gelsolin, calmodulin-binding and serine-rich domains, suggests that MKPs can interact with distinct cellular partners, others than MAPKs. In this report, we identified a canonical mode I 14-3-3-binding motif (KLPSLP) located at the carboxy-terminal region of the wheat MKP, TMKP1.

CML8, an Arabidopsis Calmodulin-Like Protein, Plays a Role in Pseudomonas syringae Plant Immunity.

Calcium is a universal second messenger involved in various cellular processes including plant development and stress responses. Its conversion into biological responses requires the presence of calcium sensor relays such as calmodulin (CaM) and calmodulin-like (CML) proteins. While the role of CaM is well described, the functions CML proteins remain largely uncharacterized.

Calcium Sensors as Key Hubs in Plant Responses to Biotic and Abiotic Stresses.

The Ca(2+) ion is recognized as a crucial second messenger in signaling pathways coupling the perception of environmental stimuli to plant adaptive responses. Indeed, one of the earliest events following the perception of environmental changes (temperature, salt stress, drought, pathogen, or herbivore attack) is intracellular variation of free calcium concentrations. These calcium variations differ in their spatio-temporal characteristics (subcellular location, amplitude, kinetics) with the nature and strength of the stimulus and, for this reason, they are considered as signatures encrypting information from the initial stimulus.

CaM and CML emergence in the green lineage.

Calmodulin (CaM) is a well-studied calcium sensor that is ubiquitous in all eukaryotes and contributes to signaling during developmental processes and adaptation to environmental stimuli. Among eukaryotes, plants have a remarkable variety of CaM-like proteins (CMLs). The expansion of genomic data sets offers the opportunity to explore CaM and CML evolution among the green lineage from algae to land plants.

The activity of the wheat MAP kinase phosphatase 1 is regulated by manganese and by calmodulin.

MAPK phosphatases (MKPs) are negative regulators of MAPKs in eukaryotes and play key roles in the regulation of different cellular processes. However in plants, little is known about the regulation of these Dual Specific Phosphatases (DSPs) by Ca(2+) and calmodulin (CaM). Here, we showed that the wheat MKP (TMKP1) harboring a calmodulin (CaM) binding domain, binds to CaM in a Ca(2+)-dependent manner.

Calcium/calmodulin-mediated regulation of plant immunity.

Calcium is a universal messenger involved in the modulation of diverse developmental and adaptive processes in response to various physiological stimuli. Ca(2+) signals are represented by stimulus-specific Ca(2+) signatures that are sensed and translated into proper cellular responses by diverse Ca(2+) binding proteins and their downstream targets. Calmodulin (CaM) and calmodulin-like (CML) proteins are primary Ca(2+) sensors that control diverse cellular functions by regulating the activity of various target proteins.

Relationships between calcium and sphingolipid-dependent signalling pathways during the early steps of plant-pathogen interactions.

An increase in cellular calcium ion (Ca(2+)) concentration is now acknowledged to be one of the earliest events occurring during the induction of plant defence responses to a wide variety of pathogens. Sphingoid long-chain bases (LCBs) have also been recently demonstrated to be important mediators of defence-related programmed cell death during pathogen attack. Here, we present recent data highlighting how Ca(2+) and LCBs may be interconnected to regulate cellular processes which lead either to plant susceptibility or to resistance mechanisms.

CML9, a multifunctional Arabidopsis thaliana calmodulin-like protein involved in stress responses and plant growth?

Plants have evolved complex signaling networks to respond to their fluctuating environment and adapt their growth and development. Calcium-dependent signaling pathways play key role in the onset of these adaptive responses. In plant cells, the intracellular calcium transients are triggered by numerous stimuli and it is supposed that the large repertory of calcium sensors present in higher plants could contribute to integrate these signals in physiological responses.

CML9, an Arabidopsis calmodulin-like protein, contributes to plant innate immunity through a flagellin-dependent signalling pathway.

Many stimuli such as hormones and elicitors induce changes in intracellular calcium levels to integrate information and activate appropriate responses. The Ca(2+) signals are perceived by various Ca(2+) sensors, and calmodulin (CaM) is one of the best characterized in eukaryotes. Calmodulin-like (CML) proteins extend the Ca(2+) toolkit in plants; they share sequence similarity with the ubiquitous and highly conserved CaM but their roles at physiological and molecular levels are largely unknown.

Nuclear calcium signaling and its involvement in transcriptional regulation in plants.

Calcium is a key second messenger in signaling pathways associated with developmental and adaptive processes in plants. Stimulus-specific calcium signals, considered as calcium signatures, are translated into appropriate cellular responses through the action of various calcium-binding proteins and downstream effectors. We review here recent progress made in calcium signaling in the nucleus of plant cell.

Calmodulin and calmodulin-like proteins in plant calcium signaling.

Calmodulin (CaM) is a primary calcium sensor in all eukaryotes. It binds calcium and regulates the activity of a wide range of effector proteins in response to calcium signals. The list of CaM targets includes plant-specific proteins whose functions are progressively being elucidated.

Involvement of RD20, a member of caleosin family, in ABA-mediated regulation of germination in Arabidopsis thaliana.

The RD20 gene encodes a member of the caleosin family, which is primarily known to function in the mobilization of seed storage lipids during germination. In contrast to other caleosins, RD20 expression is early-induced by water deficit conditions and we recently provided genetic evidence for its positive role in drought tolerance in Arabidopsis. RD20 is also responsive to pathogen infection and is constitutively expressed in diverse tissues and organs during development suggesting additional roles for this caleosin.

Heat-inducible RNAi for gene functional analysis in plants.

Controlling gene expression during plant development is an efficient method to explore gene function and RNA interference (RNAi) is now considered as a powerful technology for gene functional analysis. However, constitutive gene silencing cannot be used with genes involved in fundamental processes such as embryo viability or plant growth and alternative silencing strategies avoiding these limitations should be preferred. Tissue-specific and inducible promoters, able to control gene expression at spatial and/or temporal level, can be used to circumvent viability problems.

RD20, a stress-inducible caleosin, participates in stomatal control, transpiration and drought tolerance in Arabidopsis thaliana.

Plants overcome water deficit conditions by combining molecular, biochemical and morphological changes. At the molecular level, many stress-responsive genes have been isolated, but knowledge of their physiological functions remains fragmentary. Here, we report data for RD20, a stress-inducible Arabidopsis gene that belongs to the caleosin family.

Interaction of a plant pseudo-response regulator with a calmodulin-like protein.

Calmodulin (CaM) plays a crucial role in the regulation of diverse cellular processes by modulating the activities of numerous target proteins. Plants possess an extended CaM family including numerous CaM-like proteins (CMLs), most of which appear to be unique to plants. We previously demonstrated a role for CML9 in abiotic stress tolerance and seed germination in Arabidopsis thaliana.