Root hair formation: F-actin-dependent tip growth is initiated by local assembly of profilin-supported F-actin meshworks accumulated within expansin-enriched bulges.
Plant root hair formation is initiated when specialized elongating root epidermis cells (trichoblasts) assemble distinct domains at the plasma membrane/cell wall cell periphery complexes facing the root surface. These localities show accumulation of expansin and progressively transform into tip-growing root hair apices. Experimentation showed that trichoblasts made devoid of microtubules (MTs) were unaffected in root hair formation, whereas those depleted of F-actin by the G-actin sequestering agent latrunculin B had their root hair formation blocked after the bulge formation stage. In accordance with this, MTs are naturally depleted from early outgrowing bulges in which dense F-actin meshworks accumulate. These F-actin caps remain associated with tips of emerging and growing root hairs. Constitutive expression of the GFP-mouse talin fusion protein in transgenic Arabidopsis, which visualizes all classes of F-actin in a noninvasive mode, allowed in vivo confirmation of the presence of distinct F-actin meshworks within outgrowing bulges and at tips of young root hairs. Profilin accumulates, at both the protein and the mRNA levels, within F-actin-enriched bulges and at tips of emerging hairs. ER-based calreticulin and HDEL proteins also accumulate within outgrowing bulges and remain enriched at tips of emerging hairs. All this suggests that installation of the actin-based tip growth machinery takes place only after expansin-associated bulge formation and requires assembly of profilin-supported dynamic F-actin meshworks.
Baluska
F
F
Institute of Botany, Department of Plant Cell Biology, Rheinische Friedrich-Wilhelms University Bonn, Kirschallee 1, Bonn, D-53115, Germany. baluska@uni-bonn.de
Salaj
J
J
Mathur
J
J
Braun
M
M
Jasper
F
F
Samaj
J
J
Chua
N H
NH
Barlow
P W
PW
Volkmann
D
D
D000199:Actins / Q000378:metabolism*; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins; D003285:Contractile Proteins; D017931:DNA Primers / Q000235:genetics; D049452:Green Fluorescent Proteins; D017403:In Situ Hybridization; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D008870:Microtubules / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D051304:Profilins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D016608:Talin / Q000235:genetics; D003313:Zea mays / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
D000199:Actins; D029681:Arabidopsis Proteins; D003285:Contractile Proteins; D017931:DNA Primers; D008164:Luminescent Proteins; D008840:Microfilament Proteins; C495746:PRF1 protein, Arabidopsis; C495739:Pfn1 protein, mouse; D010940:Plant Proteins; D051304:Profilins; D012333:RNA, Messenger; D018749:RNA, Plant; D016608:Talin; C095825:expansin protein, plant; D049452:Green Fluorescent Proteins