title: Glutamate signalling via a MEKK1 kinase-dependent pathway induces changes in Arabidopsis root architecture.
abstract: A chemical genetic approach has been used to investigate the mechanism by which external glutamate (l-Glu) is able to trigger major changes in root architecture in Arabidopsis thaliana L. An initial screen of 80 agonists and antagonists of mammalian glutamate and GABA receptors, using a specially developed 96-well microphenotyping system, found none that replicated the response of the root to l-Glu or antagonized it. However, a larger screen using >1500 molecules bioactive in Saccharomyces cerevisiae (yeast) identified two groups that interfered with the l-Glu response. One of the antagonists, 2-(4-chloro-3-methylphenyl)-2-oxoethyl thiocyanate (CMOT), has been reported to target Ste11, an evolutionarily conserved MAP kinase kinase kinase (MAP3K) in yeast. This led to the discovery that root growth in a triple mekk1 mekk2 mekk3 mutant (mekk1/2/3), defective in a set of three tandemly arranged MAP3Ks, was almost insensitive to l-Glu. However, the sensitivity of mekk1/2/3 roots to inhibition by other amino acids reported to act as agonists of glutamate receptor-like (GLR) channels in Arabidopsis roots (Asn, Cys, Gly and Ser) was unaffected. The l-Glu sensitivity of the mekk1/2/3 mutant was restored by transformation with a construct carrying the intact MEKK1 gene. These results demonstrate that MEKK1 plays a key role in transducing the l-Glu signal that elicits large-scale changes in root architecture, and provide genetic evidence for the existence in plants of an l-Glu signalling pathway analogous to that found in animals.
authors.affiliation: Centre for Sustainable Agriculture, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Forde
authors.affiliation: Department of Botany and Plant Sciences, Center for Plant Biology, University of California, Riverside, CA, 92521, USA.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Cutler
authors.affiliation: Genome Center of Wisconsin and Department of Horticulture, University of Wisconsin-Madison, 1575 Linden Drive, Madison, WI, 53706, USA.
authors.forename: Najia
authors.initials: N
authors.lastname: Zaman
authors.affiliation: Genome Center of Wisconsin and Department of Horticulture, University of Wisconsin-Madison, 1575 Linden Drive, Madison, WI, 53706, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Krysan
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000033:anatomy & histology / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018698:Glutamic Acid / Q000378:metabolism*; D048728:MAP Kinase Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D009154:Mutation; D018517:Plant Roots / Q000033:anatomy & histology / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified; D011760:Pyrrolidinones / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000033:anatomy & histology / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D054852:Small Molecule Libraries; D013861:Thiocyanates / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D029681:Arabidopsis Proteins; D011760:Pyrrolidinones; D054852:Small Molecule Libraries; D013861:Thiocyanates; D018698:Glutamic Acid; D048728:MAP Kinase Kinase Kinase 1