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301.
Sentinels at the wall: cell wall receptors and sensors 总被引:6,自引:2,他引:4
The emerging view of the plant cell wall is of a dynamic and responsive structure that exists as part of a continuum with the plasma membrane and cytoskeleton. This continuum must be responsive and adaptable to normal processes of growth as well as to stresses such as wounding, attack from pathogens and mechanical stimuli. Cell expansion involving wall loosening, deposition of new materials, and subsequent rigidification must be tightly regulated to allow the maintenance of cell wall integrity and co-ordination of development. Similarly, sensing and feedback are necessary for the plant to respond to mechanical stress or pathogen attack. Currently, understanding of the sensing and feedback mechanisms utilized by plants to regulate these processes is limited, although we can learn from yeast, where the signalling pathways have been more clearly defined. Plant cell walls possess a unique and complicated structure, but it is the protein components of the wall that are likely to play a crucial role at the forefront of perception, and these are likely to include a variety of sensor and receptor systems. Recent plant research has yielded a number of interesting candidates for cell wall sensors and receptors, and we are beginning to understand the role that they may play in this crucial aspect of plant biology. 相似文献
302.
Osmotin is a pathogenesis-related protein exhibiting cryoprotective functions. Our aim was to understand whether it is involved
in the cold acclimation of the olive tree (Olea europaea L.), a frost-sensitive species lacking dormancy. We exposed olive trees expressing tobacco osmotin gene under the 35S promoter (35S:osm) [in the same manner as wild type (wt) plants] to cold shocks in the presence/absence of cold acclimation, and monitored
changes in programmed cell death (PCD), cytoskeleton, and calcium ([Ca2+]c) signalling. In the wt, osmotin was immunolocalized only in cold-acclimated plants, and in the tissues showing PCD. In the
35S:osm clones, the protein was detected also in the non-acclimated plants, and always in the tissues exhibiting PCD. In the non-acclimated
wt protoplasts exposed to cold shock, a transient decrease in phallotoxin signal suggests a temporary disassembly of F-actin,
a transient increase occurred instead in 35S:osm protoplasts exposed to the same shock. Transient increases in [Ca2+]c were observed only in the wt protoplasts. However, when F-actin was depolymerized by cytochalasin or latrunculin, and microtubules
by colchicine, increase in [Ca2+]c also occurred in the 35S:osm protoplasts. Successive cold shocks caused transient rises in [Ca2+]c and transient decreases in the phallotoxin signal in wt protoplasts. No change occurred in [Ca2+]c occurred in the 35S:osm protoplasts. The phallotoxin signal transiently increased at the first shock, but did not change after the subsequent shocks,
and an overall signal reduction occurred with shock repetition. Following acclimation, no cold shock-induced change in [Ca2+]c levels and F-actin signal occurred either in wt or 35S:osm protoplasts. The results show that osmotin is positively involved in the acclimation-related PCD, in blocking the cold-induced
calcium signalling, and in affecting cytoskeleton in response to cold stimuli. 相似文献
303.
Induced systemic resistance (ISR) in plants: mechanism of action 总被引:1,自引:0,他引:1
Plants possess a range of active defense apparatuses that can be actively expressed in response to biotic stresses (pathogens
and parasites) of various scales (ranging from microscopic viruses to phytophagous insect). The timing of this defense response
is critical and reflects on the difference between coping and succumbing to such biotic challenge of necrotizing pathogens/parasites.
If defense mechanisms are triggered by a stimulus prior to infection by a plant pathogen, disease can be reduced. Induced
resistance is a state of enhanced defensive capacity developed by a plant when appropriately stimulated. Systemic acquired
resistance (SAR) and induced systemic resistance (ISR) are two forms of induced resistance wherein plant defenses are preconditioned
by prior infection or treatment that results in resistance against subsequent challenge by a pathogen or parasite. Selected
strains of plant growth-promoting rhizobacteria (PGPR) suppress diseases by antagonism between the bacteria and soil-borne
pathogens as well as by inducing a systemic resistance in plant against both root and foliar pathogens. Rhizobacteria mediated
ISR resembles that of pathogen induced SAR in that both types of induced resistance render uninfected plant parts more resistant
towards a broad spectrum of plant pathogens. Several rhizobacteria trigger the salicylic acid (SA)-dependent SAR pathway by
producing SA at the root surface whereas other rhizobacteria trigger different signaling pathway independent of SA. The existence
of SA-independent ISR pathway has been studied in Arabidopsis thaliana, which is dependent on jasmonic acid (JA) and ethylene signaling. Specific Pseudomonas strains induce systemic resistance in viz., carnation, cucumber, radish, tobacco, and Arabidopsis, as evidenced by an enhanced defensive capacity upon challenge inoculation. Combination of ISR and SAR can increase protection
against pathogens that are resisted through both pathways besides extended protection to a broader spectrum of pathogens than
ISR/SAR alone. Beside Pseudomonas strains, ISR is conducted by Bacillus spp. wherein published results show that several specific strains of species B. amyloliquifaciens, B. subtilis, B. pasteurii, B. cereus, B. pumilus, B. mycoides, and B.sphaericus elicit significant reduction in the incidence or severity of various diseases on a diversity of hosts. 相似文献
304.
To screen stimulators from Chinese medicinal insects for mycelial growth and polysaccharides production of Ganoderma lucidum, G. lucidum was inoculated into the media with and without supplementation of medicinal insect extracts. The ethyl acetate extract of
Eupolyphaga sinensis at 55 mg l−1 lead to significant increase in both biomass and intracellular polysaccharides (IPS) concentration from 8.53 ± 0.41 to 14.16 ± 0.43
and 1.28 ± 0.09 to 2.13 ± 0.11 g l−1, respectively. In addition, the ethyl acetate extract of Catharsius molossus at 55 mg l−1 significantly enhanced extracellular polysaccharides (EPS) production; the EPS yield increased from 350.9 ± 14.1 to 475.1 ± 15.3 mg
l−1. There were no new components in the two types of polysaccharides obtained by the addition of the insect extracts. 相似文献
305.
The transient receptor potential channel TRPV5 contributes to the apical entry pathway for transcellular calcium reabsorption
in the kidney. Acid load causes hypercalciuria in animals and humans. We have previously reported that intracellular protons
directly inhibit TRPV5. Here, we examined the effects of intracellular pH on single-channel activity of TRPV5. We found that
TRPV5 channels exhibit full and subconductance open states in excised inside–out patches of Chinese hamster ovary cells. The
slope conductance values (Na+ as a charge carrier, between −25 and −75 mV) for full and subconductance opening at intracellular pH 7.4 were 59 ± 6 and 29 ± 3 pS, respectively. Intracellular acidification
caused a small decrease in single-channel conductance. Importantly, intracellular acidification decreased open probability
for the full and subconductance states and increased probability for closing. To investigate how intracellular protons decrease
open probability of the channel, we proposed a simple three-state model for open–subconductance–closed state transition and
examined the effects of acidification on the respective forward and reverse rate constants. We found that intracellular acidification
decreases opening of TRPV5 predominantly by promoting a transition from the subconductance to the closed state. Thus, intracellular
acidification directly inhibits TRPV5 by causing a conformational change(s) leading to a decrease of open probability of TRPV5
as well as of the single-channel conductance.
Seung-Kuy Cha and Wasey Jabbar contributed equally to this work. 相似文献
306.
Bronfman FC 《Journal of neurochemistry》2007,103(Z1):91-100
Signaling by the p75 neurotrophin receptor (p75) has been implicated in diverse neuronal responses, including the control of neuronal survival versus death and axonal regeneration and growth cone collapse, involving p75 in different neuropathological conditions. There are different levels of complexity regulating p75-mediated signaling. First, p75 can interact with different ligands and co-receptors in the plasma membrane, forming tripartite complexes, whose activation result in different cellular outcomes. Moreover, it was recently described that trafficking capacities of p75 in neurons are regulating, in addition to p75 downstream interactions, also the sequential cleavage of p75. The proteolytical processing of p75 involves, first, a shedding event that releases a membrane-bound carboxiterminal fragment (p75-CTF), followed by a gamma-secretase mediated cleavage, generating a soluble intracellular domain (p75-ICD) with signaling capabilities. The first shedding event, generating a p75-CTF, is the key step to regulating the production of p75-ICD, and although the generation of p75-ICD is important for both p75-mediated control of neuronal survival and the control of neurite outgrowth, little is known how both cleavage events are regulated. In this review, we argue that both sheddases and gamma-secretase are key membrane components regulating p75-mediated signaling transduction; therefore, further attention should be paid to their roles as p75 signaling regulators. 相似文献
307.
308.
Glutamate in plants: metabolism, regulation, and signalling 总被引:10,自引:0,他引:10
Glutamate occupies a central position in amino acid metabolism in plants. The acidic amino acid is formed by the action of glutamate synthase, utilizing glutamine and 2-oxoglutarate. However, glutamate is also the substrate for the synthesis of glutamine from ammonia, catalysed by glutamine synthetase. The alpha-amino group of glutamate may be transferred to other amino acids by the action of a wide range of multispecific aminotransferases. In addition, both the carbon skeleton and alpha-amino group of glutamate form the basis for the synthesis of gamma-aminobutyric acid, arginine, and proline. Finally, glutamate may be deaminated by glutamate dehydrogenase to form ammonia and 2-oxoglutarate. The possibility that the cellular concentrations of glutamate within the plant are homeostatically regulated by the combined action of these pathways is examined. Evidence that the well-known signalling properties of glutamate in animals may also extend to the plant kingdom is reviewed. The existence in plants of glutamate-activated ion channels and their possible relationship to the GLR gene family that is homologous to ionotropic glutamate receptors (iGluRs) in animals are discussed. Glutamate signalling is examined from an evolutionary perspective, and the roles it might play in plants, both in endogenous signalling pathways and in determining the capacity of the root to respond to sources of organic N in the soil, are considered. 相似文献
309.
von Blume J Knippschild U Dequiedt F Giamas G Beck A Auer A Van Lint J Adler G Seufferlein T 《The EMBO journal》2007,26(22):4619-4633
Protein kinase D2 (PKD2), a member of the PKD family of serine/threonine kinases, is localized in various subcellular compartments including the nucleus where the kinase accumulates upon activation of G-protein-coupled receptors. We define three critical post-translational modifications required for nuclear accumulation of PKD2 in response to activation of the CCK2 receptor (CCK2R): phosphorylation at Ser706 and Ser710 within the activation loop by PKC eta leading to catalytic activity and phosphorylation at Ser244 within the zinc-finger domain, which is crucial for blocking nuclear export of active PKD2 by preventing its interaction with the Crm-1 export machinery. We identify CK1delta and epsilon as upstream activated kinases by CCK2R that phosphorylate PKD2 at Ser244. Moreover, nuclear accumulation of active PKD2 is a prerequisite for efficient phosphorylation of its nuclear substrate, HDAC7. Only nuclear, active PKD2 mediates CCK2R-induced HDAC7 phosphorylation and Nur77 expression. Thus, we define a novel, compartment-specific signal transduction pathway downstream of CCK2R that phosphorylates PKD2 at three specific sites, results in nuclear accumulation of the active kinase and culminates in efficient phosphorylation of nuclear PKD2 substrates in human gastric cancer cells. 相似文献
310.
Coccaro E Mraiche F Malo M Vandertol-Vanier H Bullis B Robertson M Fliegel L 《Molecular and cellular biochemistry》2007,302(1-2):145-155
We examined two expression systems for studying the Na+/H+ exchanger in the mammalian myocardium. Mammalian NHE1 with a hemagglutinin (HA) tag and was cloned behind the alpha myosin
heavy chain promoter. Transgenic mice were made with wild type NHE1 protein or with a hyperactive NHE1 protein mutated at
the calmodulin-binding domain. Three lines of transgenic mice were made of each cDNA with expression levels of each type varying
from high to low. Higher levels and activity of the Na+/H+ exchanger were associated with decreased long-term survival of mice, and with dilated or hypertrophic cardiomyopathy. The
exogenous NHE1 protein was present in freshly made cardiomyocytes from transgenic mice, however, expression from the alpha
myosin heavy chain promoter declined rapidly and little exogenous NHE1 was apparent on the fourth day after cardiomyocyte
isolation. To express NHE1 protein in isolated cardiomyocytes, we transferred a mutated form of the protein into an adenoviral
expression system. Infection of neonatal rat cardiomyocytes resulted in robust expression of the exogenous NHE1 protein. The
mutant form of the NHE1 protein could be distinguished from the endogenous Na+/H+ exchanger by its resistance to inhibition by amiloride analogs. Our results suggest that for in vivo studies on intact hearts
and animals, expression in transgenic mice is an appropriate system, however for long-term studies on cardiomyocytes, this
model is inappropriate due to waning expression from the alpha myosin heavy chain promoter. Therefore, infection by adenovirus
is a superior system for long-term studies on cardiomyocytes in culture. 相似文献