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Glutamate signalling and the regulation of plant growth

Reference	BB/C005120/1
Principal Investigator / Supervisor	Professor Brian Gordon Forde
Co-Investigators / Co-Supervisors
Institution	Lancaster University
Department	Biological Sciences
Funding type	Research
Value (£)	202,693
Status	Completed
Type	Research Grant
Start date	01/03/2005
End date	29/02/2008
Duration	36 months

Abstract

Glutamate is a remarkably versatile amino acid with diverse signalling roles in a wide range of organisms, suggesting that its special properties have early evolutionary origins. Arabidopsis has a family of twenty AtGLR genes closely related to the animal ionotropic glutamate receptors (iGluRs) involved in fast excitatory neurotransmission. Although their exact function is unknown, members of the AtGLR gene family are expressed throughout the plant. The circumstantial evidence therefore points to some important signalling roles for glutamate (or other amino acids) in plant biology. We have recently obtained evidence that low concentrations of glutamate (but not amino acids) can modify root morphology and root architecture in a way that suggests the ability of the root tip to sense and respond to the external presence of the amino acid. Furthermore, there is a strong genetic component to the effect, with different Arabidopsis ecotypes showing wide variations in glutamate sensitivity. We have identified a major quantitative trait locus (QTL) for glutamate sensitivity (the ROOT RESPONSE TO GLUTAMATE or RRG locus) which we have mapped to chromosome 5 using recombinant inbred lines from a Col-0 x Ler cross. Our aim in this project is to determine the genetic basis for glutamate sensing in the Arabidopsis root tip and to elucidate the cellular and physiological basis of the glutamate effect. In so doing we will be testing the hypothesis that an amino acid sensory pathway with ancient evolutionary origins has been conserved in plants and has a previously unrecognised role in regulating plant growth and development. Our specific objectives are: 1. Identification of the RRG gene using a strategy that combines QTL mapping and transcript profiling. Single Recombinant Lines (SRLs) for chromosome 5 will be used to obtain an initial map location. Transcript profiling of SRLs differing only in the interval containing the RRG locus will be used to identify potential candidate geneswithin the QTL interval that are differentially expressed. Fine mapping will be performed on homozygous recombinant F2 progeny from a cross between adjacent SRLs. 2. Validation of the candidate RRG gene by gene knockouts, DNA sequencing and genetic complementation. 3. Investigation of the mechanism the root growth response to glutamate at the cellular and physiological levels. We will examine the relative contribution of effects on cell division and cell elongation in accounting for the inhibition of root growth and the induction of root bending. We will use pharmacological approaches, aequorin lines and existing mutants to investigate the role of iGluRs, calcium signalling and hormonal signalling pathways in the root response to glutamate. 4. Identification of gene networks involved in the root response to glutamate. Microarray data generated in the course of mapping the RRG locus will be analysed to identify the genes in the rest of the genome whose expression is up- or down-regulated in the short-term response to an external glutamate stimulus, and in particular those genes whose response differs between the glutamate-sensitive and the glutamate-tolerant SRLs. A successful outcome to this project will add a new signalling molecule to the growing lexicon of compounds with hormonal properties in plants. Glutamate signalling in the root tip may be just part of a network of related amino acid signalling pathways that serve to integrate physiological and developmental processes with fluctuations in the nutrient status of the plant. Progress in elucidating glutamate signalling pathways in plants, and their physiological functions, could lead the way to a better understanding of the function of iGluRs in peripheral tissues of animals.

Summary

unavailable

Committee	Closed Committee - Genes & Developmental Biology (GDB)
Research Topics	X – not assigned to a current Research Topic
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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