The actin cytoskeleton is required to elaborate and maintain spatial patterning during trichome cell morphogenesis in Arabidopsis thaliana

Arabidopsis thaliana trichomes provide an attractive model system to dissec t molecular processes involved in the generation of shape and form in singl e cell morphogenesis in plants. We have used transgenic Arabidopsis plants carrying a GFP-talin chimeric gene to analyze the role of the actin cytoske leton in trichome cell morphogenesis. we found that during trichome cell de velopment the actin microfilaments assumed an increasing degree of complexi ty from fine filaments to thick, longitudinally stretched cables. Disruptio n of the F-actin cytoskeleton by actin antagonists produced distorted but b ranched trichomes which phenocopied trichomes of mutants belonging to the ' distorted' class. Subsequent analysis of the actin cytoskeleton in trichome s of the distorted mutants, alien, crooked, distorted1, gnarled, klunker an d wurm uncovered actin organization defects in each case. Treatments of wil d-type seedlings with microtubule-interacting drugs elicited a radically di fferent trichome phenotype characterized by isotropic growth and a severe i nhibition of branch formation; these trichomes did not show defects in acti n cytoskeleton organization, A normal actin cytoskeleton was also observed in trichomes of the zwichel mutant which have reduced branching. ZWICHEL, w hich was previously shown to encode a kinesin-like protein is thought to be involved in microtubule-linked processes. Based on our results we propose that microtubules establish the spatial patterning of trichome branches whi lst actin microfilaments elaborate and maintain the overall trichome patter n during development.