Root hair formation: F-actin-dependent tip growth is initiated by local assembly of profilin-supported F-actin meshworks accumulated within expansin-enriched bulges

Dev Biol. 2000 Nov 15;227(2):618-32. doi: 10.1006/dbio.2000.9908.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism*
  • Animals
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism
  • Arabidopsis Proteins
  • Contractile Proteins*
  • DNA Primers / genetics
  • Green Fluorescent Proteins
  • In Situ Hybridization
  • Luminescent Proteins / genetics
  • Mice
  • Microfilament Proteins / genetics
  • Microfilament Proteins / metabolism*
  • Microscopy, Confocal
  • Microtubules / metabolism
  • Plant Proteins / metabolism*
  • Plant Roots / growth & development*
  • Plant Roots / metabolism*
  • Plants, Genetically Modified
  • Profilins
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Plant / genetics
  • RNA, Plant / metabolism
  • Talin / genetics
  • Zea mays / genetics
  • Zea mays / growth & development
  • Zea mays / metabolism


  • Actins
  • Arabidopsis Proteins
  • Contractile Proteins
  • DNA Primers
  • Luminescent Proteins
  • Microfilament Proteins
  • PRF1 protein, Arabidopsis
  • Pfn1 protein, mouse
  • Plant Proteins
  • Profilins
  • RNA, Messenger
  • RNA, Plant
  • Talin
  • expansin protein, plant
  • Green Fluorescent Proteins