title: Dissecting the role of CHITINASE-LIKE1 in nitrate-dependent changes in root architecture.
abstract: The root phenotype of an Arabidopsis (Arabidopsis thaliana) mutant of CHITINASE-LIKE1 (CTL1), called arm (for anion-related root morphology), was previously shown to be conditional on growth on high nitrate, chloride, or sucrose. Mutants grown under restrictive conditions displayed inhibition of primary root growth, radial swelling, proliferation of lateral roots, and increased root hair density. We found here that the spatial pattern of CTL1 expression was mainly in the root and root tips during seedling development and that the protein localized to the cell wall. Fourier-transform infrared microspectroscopy of mutant root tissues indicated differences in spectra assigned to linkages in cellulose and pectin. Indeed, root cell wall polymer composition analysis revealed that the arm mutant contained less crystalline cellulose and reduced methylesterification of pectins. We also explored the implication of growth regulators on the phenotype of the mutant response to the nitrate supply. Exogenous abscisic acid application inhibited more drastically primary root growth in the arm mutant but failed to repress lateral branching compared with the wild type. Cytokinin levels were higher in the arm root, but there were no changes in mitotic activity, suggesting that cytokinin is not directly involved in the mutant phenotype. Ethylene production was higher in arm but inversely proportional to the nitrate concentration in the medium. Interestingly, eto2 and eto3 ethylene overproduction mutants mimicked some of the conditional root characteristics of the arm mutant on high nitrate. Our data suggest that ethylene may be involved in the arm mutant phenotype, albeit indirectly, rather than functioning as a primary signal.
authors.affiliation: Laboratory of Plant Physiology and Molecular Genetics, Université Libre de Bruxelles, B-1050 Brussels, Belgium. chermans@ulb.ac.be
authors.forename: Christian
authors.initials: C
authors.lastname: Hermans
authors.forename: Silvana
authors.initials: S
authors.lastname: Porco
authors.forename: Filip
authors.initials: F
authors.lastname: Vandenbussche
authors.forename: Sascha
authors.initials: S
authors.lastname: Gille
authors.forename: Jérôme
authors.initials: J
authors.lastname: De Pessemier
authors.forename: Dominique
authors.initials: D
authors.lastname: Van Der Straeten
authors.forename: Nathalie
authors.initials: N
authors.lastname: Verbruggen
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Bush
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000033:anatomy & histology* / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism; D005030:Ethylenes / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009566:Nitrates / Q000494:pharmacology*; D018517:Plant Roots / Q000033:anatomy & histology* / Q000187:drug effects / Q000201:enzymology*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects; D036226:Seedlings / Q000033:anatomy & histology / Q000187:drug effects / Q000235:genetics; D017550:Spectroscopy, Fourier Transform Infrared; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D005030:Ethylenes; D009566:Nitrates; D000040:Abscisic Acid; C036216:ethylene; C455513:CTL1 protein, Arabidopsis; D006026:Glycoside Hydrolases