The multistep phosphorelay （MSP） is a central signaling pathway in plants integrating a wide spectrum of hormonal and environmental inputs and controlling numerous developmental adaptations. For the thor- ough compr...The multistep phosphorelay （MSP） is a central signaling pathway in plants integrating a wide spectrum of hormonal and environmental inputs and controlling numerous developmental adaptations. For the thor- ough comprehension of the molecular mechanisms underlying the MSP-mediated signal recognition and transduction, the detailed structural characterization of individual members of the pathway is critical. In this review we describe and discuss the recently known crystal and nuclear magnetic resonance structures of proteins acting in MSP signaling in higher plants, focusing particularly on cytokinin and ethylene signaling in Arabidopsis thaliana. We discuss the range of functional aspects of available structural infor- mation including determination of ligand specificity, activation of the receptor via its autophosphorylaUon, and downstream signal transduction through the phosphorelay. We compare the plant structures with their bacterial counterparts and show that although the overall similarity is high, the differences in structural de- tails are frequent and functionally important. Finally, we discuss emerging knowledge on molecular recog- nition mechanisms in the MSP, and mention the latest findings regarding structural determinants of signaling specificity in the Arabidopsis MSP that could serve as a general model of this pathway in all higher plants.展开更多
The multi-step phosphorelay （MSP） system defines a key signal transduction pathway in plants and many eukaryotes. In this system, external stimuli first lead to the activation of a histidine kinase, followed by tran...The multi-step phosphorelay （MSP） system defines a key signal transduction pathway in plants and many eukaryotes. In this system, external stimuli first lead to the activation of a histidine kinase, followed by transfer of a phosphoryl group from the receiver domain of the kinase （HKRD） to downstream, cytosolic phosphotransfer proteins （HPs）. In order to establish the determinants of specificity for this signaling relay system, we have solved the first crystal structure of a plant HKRD, AHK5RD, in complex with one of its cognate HPs, AHP1. AHP1 binds AHK5RD via a prominent hydrogen bond docking ridge and a hydrophobic patch. These features are conserved among all AHP proteins, but differ significantly from other structurally characterized prokaryotic and eukaryotic HPs. Surface plasmon resonance experiments show that AHK5RD binds to AHP1-3 with similar, micromolar affinity, consistent with the transient nature of this signaling complex. Our correlation of structural and functional data provide the first insight, at the atomic level as well as with quantitative affinity data, into the molecular recognition events governing the MSP in plants.展开更多
Nitrogen （N） metabolism is essential for the biosynthesis of vital biomolecules. N status thus exerts profound effects on plant growth and development, and must be closely monitored. In bacteria and fungi, a few sop...Nitrogen （N） metabolism is essential for the biosynthesis of vital biomolecules. N status thus exerts profound effects on plant growth and development, and must be closely monitored. In bacteria and fungi, a few sophisticated N sensing systems have been extensively studied. In animals, the ability to receive amino acid signals has evolved to become an integral part of the nervous coordination system. In this review, we will summarize recent developments in the search for putative N sensing systems in higher plants based on homologous systems in bacteria, fungi, and animals. Apparently, although plants have separated and diversified from other organisms during the evolution process, striking similarities can be found in their N sensing systems compared with those of their counterparts; however, our understanding of these systems is still incomplete. Significant modifications of the N sensing systems （including cross-talk with other signal transduction pathways） in higher plants may be a strategy of adaptation to their unique mode of life.展开更多
Two principal growth regulators,cytokinins and ethylene,are known to interact in the regulation of plant growth.However,information about the underlying molecular mechanism and positional specificity of cytokinin/ethy...Two principal growth regulators,cytokinins and ethylene,are known to interact in the regulation of plant growth.However,information about the underlying molecular mechanism and positional specificity of cytokinin/ethylene crosstalk in the control of root growth is scarce.We have identified the spatial specificity of cytokinin-regulated root elongation and root apical meristem(RAM)size,both of which we demonstrate to be dependent on ethylene biosynthesis.Upregulation of the cytokinin biosynthetic gene ISOPENTENYLTRANSFERASE(IPT)in proximal and peripheral tissues leads to both root and RAM shortening.By contrast,IPT activation in distal and inner tissues reduces RAM size while leaving the root length comparable to that of mock-treated controls.We show that cytokinins regulate two steps specific to ethylene biosynthesis:production of the ethylene precursor 1-aminocyclopropane-1-carboxylate(ACC)by ACC SYNTHASEs(ACSs)and its conversion to ethylene by ACC OXIDASEs(ACOs).We describe cytokinin-and ethylene-specific regulation controlling the activity of ACSs and ACOs that are spatially discrete along both proximo/distal and radial root axes.Using direct ethylene measurements,we identify ACO2,ACO3,and ACO4 as being responsible for ethylene biosynthesis and ethylene-regulated root and RAM shortening in cytokinin-treated Arabidopsis.Direct interaction between ARABIDOPSIS RESPONSE REGULATOR 2(ARR2),a member of the multistep phosphorelay cascade,and the C-terminal portion of ETHYLENE INSENSITIVE 2(EIN2-C),a key regulator of canonical ethylene signaling,is involved in the cytokinin-induced,ethylene-mediated control of ACO4.We propose tight cooperation between cytokinin and ethylene signaling in the spatially specific regulation of ethylene biosynthesis as a key aspect of the hormonal control of root growth.展开更多
文摘The multistep phosphorelay （MSP） is a central signaling pathway in plants integrating a wide spectrum of hormonal and environmental inputs and controlling numerous developmental adaptations. For the thor- ough comprehension of the molecular mechanisms underlying the MSP-mediated signal recognition and transduction, the detailed structural characterization of individual members of the pathway is critical. In this review we describe and discuss the recently known crystal and nuclear magnetic resonance structures of proteins acting in MSP signaling in higher plants, focusing particularly on cytokinin and ethylene signaling in Arabidopsis thaliana. We discuss the range of functional aspects of available structural infor- mation including determination of ligand specificity, activation of the receptor via its autophosphorylaUon, and downstream signal transduction through the phosphorelay. We compare the plant structures with their bacterial counterparts and show that although the overall similarity is high, the differences in structural de- tails are frequent and functionally important. Finally, we discuss emerging knowledge on molecular recog- nition mechanisms in the MSP, and mention the latest findings regarding structural determinants of signaling specificity in the Arabidopsis MSP that could serve as a general model of this pathway in all higher plants.
文摘The multi-step phosphorelay （MSP） system defines a key signal transduction pathway in plants and many eukaryotes. In this system, external stimuli first lead to the activation of a histidine kinase, followed by transfer of a phosphoryl group from the receiver domain of the kinase （HKRD） to downstream, cytosolic phosphotransfer proteins （HPs）. In order to establish the determinants of specificity for this signaling relay system, we have solved the first crystal structure of a plant HKRD, AHK5RD, in complex with one of its cognate HPs, AHP1. AHP1 binds AHK5RD via a prominent hydrogen bond docking ridge and a hydrophobic patch. These features are conserved among all AHP proteins, but differ significantly from other structurally characterized prokaryotic and eukaryotic HPs. Surface plasmon resonance experiments show that AHK5RD binds to AHP1-3 with similar, micromolar affinity, consistent with the transient nature of this signaling complex. Our correlation of structural and functional data provide the first insight, at the atomic level as well as with quantitative affinity data, into the molecular recognition events governing the MSP in plants.
基金Supported by the Hong Kong UGC Area of Excellence on Plant and Fungal Biotechnology Center and Hong Kong RGC earmarked grant CUHK4263/ 00M
文摘Nitrogen （N） metabolism is essential for the biosynthesis of vital biomolecules. N status thus exerts profound effects on plant growth and development, and must be closely monitored. In bacteria and fungi, a few sophisticated N sensing systems have been extensively studied. In animals, the ability to receive amino acid signals has evolved to become an integral part of the nervous coordination system. In this review, we will summarize recent developments in the search for putative N sensing systems in higher plants based on homologous systems in bacteria, fungi, and animals. Apparently, although plants have separated and diversified from other organisms during the evolution process, striking similarities can be found in their N sensing systems compared with those of their counterparts; however, our understanding of these systems is still incomplete. Significant modifications of the N sensing systems （including cross-talk with other signal transduction pathways） in higher plants may be a strategy of adaptation to their unique mode of life.
基金Ministry of Education,Youth and Sports of the Czech Republic under the projects TANGENC(CZ.02.01.01/00/22_008/0004581)and LUAUS24277German Research Foundation(CRC 1101 project D02)+1 种基金Howard Hughes Medical Institute(to E.M.M.)Russian Science Foundation(20-14-00140).
文摘Two principal growth regulators,cytokinins and ethylene,are known to interact in the regulation of plant growth.However,information about the underlying molecular mechanism and positional specificity of cytokinin/ethylene crosstalk in the control of root growth is scarce.We have identified the spatial specificity of cytokinin-regulated root elongation and root apical meristem(RAM)size,both of which we demonstrate to be dependent on ethylene biosynthesis.Upregulation of the cytokinin biosynthetic gene ISOPENTENYLTRANSFERASE(IPT)in proximal and peripheral tissues leads to both root and RAM shortening.By contrast,IPT activation in distal and inner tissues reduces RAM size while leaving the root length comparable to that of mock-treated controls.We show that cytokinins regulate two steps specific to ethylene biosynthesis:production of the ethylene precursor 1-aminocyclopropane-1-carboxylate(ACC)by ACC SYNTHASEs(ACSs)and its conversion to ethylene by ACC OXIDASEs(ACOs).We describe cytokinin-and ethylene-specific regulation controlling the activity of ACSs and ACOs that are spatially discrete along both proximo/distal and radial root axes.Using direct ethylene measurements,we identify ACO2,ACO3,and ACO4 as being responsible for ethylene biosynthesis and ethylene-regulated root and RAM shortening in cytokinin-treated Arabidopsis.Direct interaction between ARABIDOPSIS RESPONSE REGULATOR 2(ARR2),a member of the multistep phosphorelay cascade,and the C-terminal portion of ETHYLENE INSENSITIVE 2(EIN2-C),a key regulator of canonical ethylene signaling,is involved in the cytokinin-induced,ethylene-mediated control of ACO4.We propose tight cooperation between cytokinin and ethylene signaling in the spatially specific regulation of ethylene biosynthesis as a key aspect of the hormonal control of root growth.
