title: Visualization of highly dynamic F-actin plus ends in growing phaseolus vulgaris root hair cells and their responses to Rhizobium etli nod factors.
abstract: Legume plants secrete signaling molecules called flavonoids into the rhizosphere. These molecules activate the transcription of rhizobial nod genes, which encode proteins involved in the synthesis of signaling compounds named Nod factors (NFs). NFs, in turn, trigger changes in plant gene expression, cortical cell dedifferentiation and mitosis, depolarization of the root hair cell membrane potential and rearrangement of the actin cytoskeleton. Actin polymerization plays an important role in apical growth in hyphae and pollen tubes. Using sublethal concentrations of fluorescently labeled cytochalasin D (Cyt-Fl), we visualized the distribution of filamentous actin (F-actin) plus ends in living Phaseolus vulgaris and Arabidopsis root hairs during apical growth. We demonstrated that Cyt-Fl specifically labeled the newly available plus ends of actin microfilaments, which probably represent sites of polymerization. The addition of unlabeled competing cytochalasin reduced the signal, suggesting that the labeled and unlabeled forms of the drug bind to the same site on F-actin. Exposure to Rhizobium etli NFs resulted in a rapid increase in the number of F-actin plus ends in P. vulgaris root hairs and in the re-localization of F-actin plus ends to infection thread initiation sites. These data suggest that NFs promote the formation of F-actin plus ends, which results in actin cytoskeleton rearrangements that facilitate infection thread formation.
authors.affiliation: Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, UNAM, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico.
authors.forename: Isaac
authors.initials: I
authors.lastname: Zepeda
authors.forename: Rosana
authors.initials: R
authors.lastname: Sánchez-López
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Kunkel
authors.forename: Luis A
authors.initials: LA
authors.lastname: Bañuelos
authors.forename: Alejandra
authors.initials: A
authors.lastname: Hernández-Barrera
authors.forename: Federico
authors.initials: F
authors.lastname: Sánchez
authors.forename: Carmen
authors.initials: C
authors.lastname: Quinto
authors.forename: Luis
authors.initials: L
authors.lastname: Cárdenas
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D027805:Phaseolus / Q000187:drug effects* / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D000199:Actins; D008070:Lipopolysaccharides; C092533:Nod factor, Rhizobium etli
keywords: Fluorescently labeled cytochalasin D; Infection thread; Nodulation; Root hair; Tip growth