Ethylene is a plant hormone that regulates many aspects of growth and development. Despite the well-known association between ethylene and stress signalling, its effects on stomatal movements are ...largely unexplored. Here, genetic and physiological data are provided that position ethylene into the Arabidopsis guard cell signalling network, and demonstrate a functional link between ethylene and hydrogen peroxide (H₂O₂). In wild-type leaves, ethylene induces stomatal closure that is dependent on H₂O₂ production in guard cells, generated by the nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase AtrbohF. Ethylene-induced closure is inhibited by the ethylene antagonists 1-MCP and silver. The ethylene receptor mutants etr1-1 and etr1-3 are insensitive to ethylene in terms of stomatal closure and H₂O₂ production. Stomata of the ethylene signalling ein2-1 and arr2 mutants do not close in response to either ethylene or H₂O₂ but do generate H₂O₂ following ethylene challenge. Thus, the data indicate that ethylene and H₂O₂ signalling in guard cells are mediated by ETR1 via EIN2 and ARR2-dependent pathway(s), and identify AtrbohF as a key mediator of stomatal responses to ethylene.
The ability of plants to adapt to multiple stresses imposed by the natural environment requires cross-talk and fine-tuning of stress signalling pathways. The hybrid histidine kinase Arabidopsis ...histidine kinase 5 (AHK5) is known to mediate stomatal responses to exogenous and endogenous signals in Arabidopsis thaliana. The purpose of this study was to determine whether the function of AHK5 in stress signalling extends beyond stomatal responses.
Plant growth responses to abiotic stresses, tissue susceptibility to bacterial and fungal pathogens, and hormone production and metabolism of reactive oxygen species were monitored in a T-DNA insertion mutant of AHK5.
The findings of this study indicate that AHK5 positively regulates salt sensitivity and contributes to resistance to the bacterium Pseudomonas syringae pv. tomato DC3000 and the fungal pathogen Botrytis cinerea.
This is the first report of a role for AHK5 in the regulation of survival following challenge by a hemi-biotrophic bacterium and a necrotrophic fungus, as well as in the growth response to salt stress. The function of AHK5 in regulating the production of hormones and redox homeostasis is discussed.
Oxidative stress, resulting from an imbalance in the accumulation and removal of reactive oxygen species such as hydrogen peroxide (H2O2), is a challenge faced by all aerobic organisms. In plants, ...exposure to various abiotic and biotic stresses results in accumulation of H2O2 and oxidative stress. Increasing evidence indicates that H2O2 functions as a stress signal in plants, mediating adaptive responses to various stresses. To analyze cellular responses to H2O2, we have undertaken a large-scale analysis of the Arabidopsis transcriptome during oxidative stress. Using cDNA microarray technology, we identified 175 non-redundant expressed sequence tags that are regulated by H2O2. Of these, 113 are induced and 62 are repressed by H2O2. A substantial proportion of these expressed sequence tags have predicted functions in cell rescue and defense processes. RNA-blot analyses of selected genes were used to verify the microarray data and extend them to demonstrate that other stresses such as wilting, UV irradiation, and elicitor challenge also induce the expression of many of these genes, both independently of, and, in some cases, via H2O2.
Just like the human gut microbiome (population of microbes), which enables a healthy immune system, the plant microbiome in the roots (rhizobiome) is unique to each plant and provides a healthy ...lifestyle. ...PGPR release chemicals and make soil minerals more available to the plant; this enhances the plant's fitness towards environmental stresses such as drought, salinity, heat, and heavy metals. Some bacteria living in soils use a special enzyme (nitrogenase) to change (or 'fix') atmospheric nitrogen into ammonia under anaerobic conditions; plants then use the ammonia to form essential molecules.
The role of Δ4-unsaturated sphingolipid long-chain bases such as sphingosine was investigated in Arabidopsis (Arabidopsis thaliana). Identification and functional characterization of the sole ...Arabidopsis ortholog of the sphingolipid Δ4-desaturase was achieved by heterologous expression in Pichia pastoris. A P. pastoris mutant disrupted in the endogenous sphingolipid Δ4-desaturase gene was unable to synthesize glucosylceramides. Synthesis of glucosylceramides was restored by the expression of Arabidopsis gene At4g04930, and these sphingolipids were shown to contain Δ4-unsaturated long-chain bases, confirming that this open reading frame encodes the sphingolipid Δ4-desaturase. At4g04930 has a very restricted expression pattern, transcripts only being detected in pollen and floral tissues. Arabidopsis insertion mutants disrupted in the sphingolipid Δ4-desaturase At4g04930 were isolated and found to be phenotypically normal. Sphingolipidomic profiling of a T-DNA insertion mutant indicated the absence of Δ4-unsaturated sphingolipids in floral tissue, also resulting in the reduced accumulation of glucosylceramides. No difference in the response to drought or water loss was observed between wild-type plants and insertion mutants disrupted in the sphingolipid Δ4-desaturase At4g04930, nor was any difference observed in stomatal closure after treatment with abscisic acid. No differences in pollen viability between wild-type plants and insertion mutants were detected. Based on these observations, it seems unlikely that Δ4-unsaturated sphingolipids and their metabolites such as sphingosine-1-phosphate play a significant role in Arabidopsis growth and development. However, Δ4-unsaturated ceramides may play a previously unrecognized role in the channeling of substrates for the synthesis of glucosylceramides.
Stomatal guard cells monitor and respond to environmental and endogenous signals such that the stomatal aperture is continually optimised for water use efficiency. A key signalling molecule produced ...in guard cells in response to plant hormones, light, carbon dioxide and pathogen-derived signals is hydrogen peroxide (H(2)O(2)). The mechanisms by which H(2)O(2) integrates multiple signals via specific signalling pathways leading to stomatal closure is not known.
Here, we identify a pathway by which H(2)O(2), derived from endogenous and environmental stimuli, is sensed and transduced to effect stomatal closure. Histidine kinases (HK) are part of two-component signal transduction systems that act to integrate environmental stimuli into a cellular response via a phosphotransfer relay mechanism. There is little known about the function of the HK AHK5 in Arabidopsis thaliana. Here we report that in addition to the predicted cytoplasmic localisation of this protein, AHK5 also appears to co-localise to the plasma membrane. Although AHK5 is expressed at low levels in guard cells, we identify a unique role for AHK5 in stomatal signalling. Arabidopsis mutants lacking AHK5 show reduced stomatal closure in response to H(2)O(2), which is reversed by complementation with the wild type gene. Over-expression of AHK5 results in constitutively less stomatal closure. Abiotic stimuli that generate endogenous H(2)O(2), such as darkness, nitric oxide and the phytohormone ethylene, also show reduced stomatal closure in the ahk5 mutants. However, ABA caused closure, dark adaptation induced H(2)O(2) production and H(2)O(2) induced NO synthesis in mutants. Treatment with the bacterial pathogen associated molecular pattern (PAMP) flagellin, but not elf peptide, also exhibited reduced stomatal closure and H(2)O(2) generation in ahk5 mutants.
Our findings identify an integral signalling function for AHK5 that acts to integrate multiple signals via H(2)O(2) homeostasis and is independent of ABA signalling in guard cells.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Hydrogen peroxide (H
2O
2) is now recognised as a key signalling molecule in eukaryotes. In plants, H
2O
2 is involved in regulating stomatal closure, gravitropic responses, gene expression and ...programmed cell death. Although several kinases, such as oxidative signal-inducible 1 (OXI1) kinase and mitogen-activated protein kinases are known to be activated by exogenous H
2O
2, little is known about the proteins that directly react with H
2O
2. Here, we utilised a proteomic approach, using iodoacetamide-based fluorescence tagging of proteins in conjunction with mass spectrometric analysis, to identify several proteins that might be potential targets of H
2O
2 in the cytosolic fraction of
Arabidopsis thaliana, the most prominent of which was cytosolic glyceraldehyde 3-phosphate dehydrogenase (cGAPDH; EC 1.2.1.12). cGAPDH from
Arabidopsis is inactivated by H
2O
2 in vitro, and this inhibition is reversible by the subsequent addition of reductants such as reduced glutathione (GSH). It has been suggested recently that
Arabidopsis GAPDH has roles outside of its catalysis as part of glycolysis, while in other systems this includes that of mediating reactive oxygen species (ROS) signalling. Here, we suggest that cGAPDH in
Arabidopsis might also have such a role in mediating ROS signalling in plants.
Histidine kinases have been shown to mediate responses to endogenous and exogenous stimuli in organisms such as yeast, bacteria and plants. In the model plant Arabidopsis, histidine kinases have been ...shown to function in hormone signaling, and abiotic and biotic stress responses. More recently, the least characterized of the Arabidopsis histidine kinases, AHK5, was demonstrated to function in resistance toward the virulent bacterium Pseudomonas syringae pv tomato DC3000 (PstDC3000) and the necrotrophic fungus Botrytis cinerea, and as a negative regulator of tolerance toward salinity. Here, we present data which indicate that AHK5 also impacts on drought stress resistance and on the outcome of an incompatible interaction with avrRpm1-expressing PstDC3000 (PstDC3000 (avrRpm1)). We present a model which proposes a role for reactive oxygen species (ROS) and hormones in integrating abiotic and biotic stress responses via AHK5.
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