Calcium-mediated perception and defense responses activated in plant cells by metabolite mixtures secreted by the biocontrol fungus Trichoderma atroviride

<p>Abstract</p> <p>Background</p> <p>Calcium is commonly involved as intracellular messenger in the transduction by plants of a wide range of biotic stimuli, including signals from pathogenic and symbiotic fungi. <it>Trichoderma </it>spp. are largely used in the biological control of plant diseases caused by fungal phytopathogens and are able to colonize plant roots. Early molecular events underlying their association with plants are relatively unknown.</p> <p>Results</p> <p>Here, we investigated the effects on plant cells of metabolite complexes secreted by <it>Trichoderma atroviride </it>wild type P1 and a deletion mutant of this strain on the level of cytosolic free Ca²⁺and activation of defense responses. <it>Trichoderma </it>culture filtrates were obtained by growing the fungus alone or in direct antagonism with its fungal host, the necrotrophic pathogen <it>Botrytis cinerea</it>, and then separated in two fractions (>3 and <3 kDa). When applied to aequorin-expressing soybean (<it>Glycine max </it>L.) cell suspension cultures, <it>Trichoderma </it>and <it>Botrytis </it>metabolite mixtures were distinctively perceived and activated transient intracellular Ca²⁺elevations with different kinetics, specific patterns of intracellular accumulation of reactive oxygen species and induction of cell death. Both Ca²⁺signature and cellular effects were modified by the culture medium from the knock-out mutant of <it>Trichoderma</it>, defective for the production of the secreted 42 kDa endochitinase.</p> <p>Conclusion</p> <p>New insights are provided into the mechanism of interaction between <it>Trichoderma </it>and plants, indicating that secreted fungal molecules are sensed by plant cells through intracellular Ca²⁺changes. Plant cells are able to discriminate signals originating in the single or two-fungal partner interaction and modulate defense responses.</p

Functional specialization of calreticulin domains

Calreticulin is a Ca2+-binding chaperone in the endoplasmic reticulum (ER), and calreticulin gene knockout is embryonic lethal. Here, we used calreticulin-deficient mouse embryonic fibroblasts to examine the function of calreticulin as a regulator of Ca2+ homeostasis. In cells without calreticulin, the ER has a lower capacity for Ca2+ storage, although the free ER luminal Ca2+ concentration is unchanged. Calreticulin-deficient cells show inhibited Ca2+ release in response to bradykinin, yet they release Ca2+ upon direct activation with the inositol 1,4,5-trisphosphate (InsP3). These cells fail to produce a measurable level of InsP3 upon stimulation with bradykinin, likely because the binding of bradykinin to its cell surface receptor is impaired. Bradykinin binding and bradykinin-induced Ca2+ release are both restored by expression of full-length calreticulin and the N + P domain of the protein. Expression of the P + C domain of calreticulin does not affect bradykinin-induced Ca2+ release but restores the ER Ca2+ storage capacity. Our results indicate that calreticulin may play a role in folding of the bradykinin receptor, which affects its ability to initiate InsP3-dependent Ca2+ release in calreticulin-deficient cells. We concluded that the C domain of calreticulin plays a role in Ca2+ storage and that the N domain may participate in its chaperone functions

Endoplasmic reticulum stress-induced programmed cell death in soybean cells

In animal cells, the endoplasmic reticulum may participate in programmed cell death by sensing and transducing apoptotic signals. In an attempt to analyze the role of the endoplasmic reticulum in plant programmed cell death we investigated the effect of cyclopiazonic acid, a specific blocker of plant endoplasmic reticulum-type IIA Ca2+-pumps, in soybean cells. Cyclopiazonic acid treatment elicited endoplasmic reticulum stress and a biphasic increase in cytosolic Ca2+ concentration, followed by the induction of a cell death program. Cyclopiazonic acid-induced programmed cell death occurred with accumulation of H2O2, cytochrome c release from mitochondria, caspase 9- and caspase 3-like protease activation, cytoplasmic shrinkage and chromatin condensation. Chelation of cytosolic Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethil ester) failed to inhibit cyclopiazonic acid-induced cell death. Taken together, our results provide evidence for a role of the endoplasmic reticulum and mitochondria in regulating cyclopiazonic acid-induced programmed cell death in soybean cells, probably via a cross-talk between the two organelles

Stress-induced programmed cell death in the unicellular alga " Chlorella" saccharophila-like

17-23 July 2005, Vienna, Austri

Monitoring programmed cell death triggered by mild heat shock in soybean-cultured cells

Programmed cell death (PCD) is a common form of cellular demise during plant response to environmental stresses. The pathway of PCD has been partially clarified in plants although the underlying molecular mechanisms are still poorly defined. We have investigated the signalling cascade induced by a mild heat treatment causingPCDin soybean cells (Glycine max L.). The data showthat heat shock led to the onset ofPCDin soybean cells involving H2O2 production and mitochondrial damage. Cytochrome c release accompanies the presence of caspase 9-like and caspase 3-like protease activities. Concomitantly, cells were severely damaged with a progressive cell shrinkage, chloroplast alteration and detachment of the plasma membrane from the cellwall. Chromatin condensation and DNA damage were observed. It is proposed that a mild heat stress induces PCD in soybean cells through a caspase-like-dependent pathway

Programmed Cell Death And Adaptation: Two Different Types Of Abiotic Stress Response In A Unicellular Chlorophyte

Eukaryotic microalgae are highly suitable biological indicators of environmental changes because they are exposed to extreme seasonal fl uctuations. The biochemical and molecular targets and regulators of key proteins involved in the stress response in microalgae have yet to be elucidated. This study presents morphological and biochemical evidence of programmed cell death (PCD) in a low temperature strain of Chlorella saccharophila induced by exposure to NaCl stress. Morphological characteristics of PCD, including cell shrinkage, detachment of the plasma membrane from the cell wall, nuclear condensation and DNA fragmentation, were observed. Additionally, a signifi cant production of H 2 O 2 and increase in caspase 3-like activity were detected. We demonstrated that singly applied environmental stresses such as warming or salt stress trigger a pathway of PCD. Intriguingly, the prior application of salt stress seems to reduce heat shock-induced cell death signifi cantly, suggesting a combined effect which activates a defense mechanism in algal cells. These results suggest that C. saccharophila can undergo PCD under stress conditions, and that this PCD shares several features with metazoan PCD. Moreover, the simultaneous exposure of this unicellular chlorophyte to different abiotic stresses results in a tolerance mechanism