title: Regulation of root hair initiation and expansin gene expression in Arabidopsis.
abstract: The expression of two Arabidopsis expansin genes (AtEXP7 and AtEXP18) is tightly linked to root hair initiation; thus, the regulation of these genes was studied to elucidate how developmental, hormonal, and environmental factors orchestrate root hair formation. Exogenous ethylene and auxin, as well as separation of the root from the medium, stimulated root hair formation and the expression of these expansin genes. The effects of exogenous auxin and root separation on root hair formation required the ethylene signaling pathway. By contrast, blocking the endogenous ethylene pathway, either by genetic mutations or by a chemical inhibitor, did not affect normal root hair formation and expansin gene expression. These results indicate that the normal developmental pathway for root hair formation (i.e., not induced by external stimuli) is independent of the ethylene pathway. Promoter analyses of the expansin genes show that the same promoter elements that determine cell specificity also determine inducibility by ethylene, auxin, and root separation. Our study suggests that two distinctive signaling pathways, one developmental and the other environmental/hormonal, converge to modulate the initiation of the root hair and the expression of its specific expansin gene set.
authors.affiliation: Department of Biology, Pennsylvania State University, 208 Mueller Laboratory, University Park, Pennsylvania 16802, USA. hxc31@psu.edu
authors.forename: Hyung-Taeg
authors.initials: HT
authors.lastname: Cho
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Cosgrove
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D003521:Cyclopropanes / Q000494:pharmacology; D005030:Ethylenes / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000494:pharmacology; D008969:Molecular Sequence Data; D010937:Plant Growth Regulators / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D011401:Promoter Regions, Genetic / Q000235:genetics
chemical_list: C472143:AT-EXP18 protein, Arabidopsis; D029681:Arabidopsis Proteins; C472142:AtEXP7 protein, Arabidopsis; D003521:Cyclopropanes; D005030:Ethylenes; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; C095825:expansin protein, plant; C105498:1-methylcyclopropane; C036216:ethylene