Abstract
Plants have evolved an elaborate system to cope with a variety of biotic and abiotic stresses. Typically, under stress conditions an appropriate defense response is invoked which is accompanied by changes in the metabolic status of the plant. Photosynthesis is downregulated and sucrose is imported into the tissue, which provides a faster and more constant flux of energy and carbon skeletons to perform the defense response. Interestingly, these processes are co-ordinately regulated and the signal transduction chains underlying these cellular programs appear to share at least some common elements. Both the induction of sink metabolism and defense response is dependent on signal transduction pathways involving protein phosphorylation. Furthermore, regulation of extracellular invertase (INV) and phenylalanine ammonia lyase (PAL) which are markers for sink metabolism and defense response is preceded by the transient activation of MAP kinases. In depth analysis of MAP kinase activation by partial purification led to the discovery that, depending on the stimulus, different subsets of MAP kinases are activated. This differential MAPK activation is likely to possess a signal encoding function. In addition, the partial purification of MAP kinases was found to be suitable to address specific cellular functions to individual MAP kinase isoenzymes. By this way, LpWIPK was identified as the major MAP kinase activity induced after stimulation of tomato cells with different elicitors. LpWIPK is thus considered as a key regulator of defense response together with sink induction in tomato. A study using nonmetabolisable sucrose analogs revealed that the regulation of photosynthesis is not directly coupled to this signal transduction pathway since it is independent of MAP kinase activation. Nonetheless, downregulation is induced by the same stimuli that induce the defense response and sink metabolism and it will therefore be interesting to uncover the branch points of this signalling network in the future. MAP kinases are not only central components regulating the response to biotic stresses. In addition to e.g. pathogens, MAP kinases are as well involved in signal transduction events invoked by abiotic stresses like cold and drought. In a recent study, we could show that a MAP kinase is activated by heat stress, under conditions a plant will encounter in nature. This previously unknown MAP kinase is able to specifically recognise the heat stress transcription factor HsfA3 as a substrate, which supports a role of this MAP kinase in the regulation of the heat stress response. Moreover, the observation that HsfA3 is phosphorylated by the heat activated MAP kinase in vitro provides a promising basis to identify HsfA3 as the first physiological substrate of a plant MAP kinase. Intracellular protons have been implicated in the signal transduction of defense related signals. In a study using Chenopodium rubrum cells, we could show that cytosolic changes in pH values do not precede the regulation of the marker genes INV and PAL. Depending on the stimulus applied, cytosolic acidification or alkalinisation can be observed, which excludes a role for protons as signals in this pathway. Together with the concomitant changes of the pH value of the extracellular space, these variations can thus be considered as terminal part of the defense response itself rather than as a second messenger. WRKY transcription factors have only recently been identified as indirect targets of a central plant MAP kinase cascade. In addition, the identification of cognate binding sites in the promoters of INV and PAL supports a role for these proteins in the co-ordinate regulation of defense response and sink induction. A novel elicitor responsive WRKY transcription factor, LpWRKY1, was cloned from tomato and characterised with respect to its posttranslational modification. This immediate early transcription factor is transiently induced upon pathogen attack and the induction is dependent on phosphorylation. Furthermore, it was shown for the first time with respect to WRKY transcription factors, that LpWRKY1 is phosphorylated in vivo. Analysis of the role of this phosphorylation by in gel assays using recombinant WRKY protein as the substrate revealed two protein kinases that are transiently activated during the defense response to phosphorylate LpWRKY1. This data demonstrates that WRKY proteins require phosphorylation to modulate their DNA binding or transactivating activity.
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Claims 11
Claim · model-written summary
Different subsets of MAP kinases are activated depending on the stimulus.
Not reportedTaxon
Verbatim
e1“depending on the stimulus, different subsets of MAP kinases are activated”
Claim · model-written summary
LpWIPK was identified as the major MAP kinase activity induced after stimulation of tomato cells with different elicitors.
- Taxon
- tomato
Solanum lycopersicume1 - Treatment
- different elicitorse1
- Gene
- LpWIPKe1
- Outcome
- major MAP kinase activity inducede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“LpWIPK was identified as the major MAP kinase activity induced after stimulation of tomato cells with different elicitors”
Claim · model-written summary
LpWIPK is considered a key regulator of defense response together with sink induction in tomato.
- Taxon
- tomatoSolanum lycopersicume1
- Gene
- LpWIPKe1
- Outcome
- defense response together with sink inductione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“LpWIPK is thus considered as a key regulator of defense response together with sink induction in tomato”
Claim · model-written summary
Regulation of photosynthesis is not directly coupled to the MAP kinase signal transduction pathway, since it is independent of MAP kinase activation.
Not reportedTaxon
Verbatim
e1“the regulation of photosynthesis is not directly coupled to this signal transduction pathway since it is independent of MAP kinase activation”
Claim · model-written summary
A MAP kinase is activated by heat stress under conditions a plant will encounter in nature.
Not reportedTaxon
Verbatim
e1“we could show that a MAP kinase is activated by heat stress, under conditions a plant will encounter in nature”
Claim · model-written summary
The newly found heat-activated MAP kinase specifically recognises the heat stress transcription factor HsfA3 as a substrate.
Not reportedTaxon
Verbatim
e1“This previously unknown MAP kinase is able to specifically recognise the heat stress transcription factor HsfA3 as a substrate”
Claim · model-written summary
In Chenopodium rubrum cells, cytosolic changes in pH do not precede the regulation of the marker genes INV and PAL.
- Taxon
- Chenopodium rubrum
Oxybasis rubrae1 - Gene
- INV and PALe1
- Outcome
- cytosolic changes in pH valuese1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In a study using Chenopodium rubrum cells, we could show that cytosolic changes in pH values do not precede the regulation of the marker genes INV and PAL”
Claim · model-written summary
The elicitor-responsive WRKY transcription factor LpWRKY1 was cloned from tomato.
- Taxon
- tomatoSolanum lycopersicume1
- Gene
- LpWRKY1e1
- Outcome
- clonede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“A novel elicitor responsive WRKY transcription factor, LpWRKY1, was cloned from tomato”
Claim · model-written summary
LpWRKY1 is transiently induced upon pathogen attack and the induction is dependent on phosphorylation.
- Taxon
- tomatoSolanum lycopersicume0
- Gene
- LpWRKY1e0
- Outcome
- transiently induced upon pathogen attacke1
- Qualifier
- dependent on phosphorylatione1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A novel elicitor responsive WRKY transcription factor, LpWRKY1, was cloned from tomato”
e1“This immediate early transcription factor is transiently induced upon pathogen attack and the induction is dependent on phosphorylation”
Claim · model-written summary
LpWRKY1 is phosphorylated in vivo, shown for the first time for WRKY transcription factors.
- Taxon
- tomatoSolanum lycopersicume0
- Gene
- LpWRKY1e1
- Outcome
- phosphorylated in vivoe1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A novel elicitor responsive WRKY transcription factor, LpWRKY1, was cloned from tomato”
e1“it was shown for the first time with respect to WRKY transcription factors, that LpWRKY1 is phosphorylated in vivo”
Claim · model-written summary
Two protein kinases are transiently activated during the defense response to phosphorylate LpWRKY1.
- Taxon
- tomatoSolanum lycopersicume0
- Gene
- LpWRKY1e1
- Outcome
- two protein kinases that are transiently activated during the defense responsee1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A novel elicitor responsive WRKY transcription factor, LpWRKY1, was cloned from tomato”
e1“revealed two protein kinases that are transiently activated during the defense response to phosphorylate LpWRKY1”