The Role of Actin during Arabidopsis Trichome Morphogenesis

Arabidopsis trichome (leaf hair) development is being used as a genetic system to study actin-dependent growth. Arabidopsis trichomes are unicellular structures that are derived from the epidermis. Trichome development has been established as a powerful model system to study the control of cell fate and pattern formation. Results from several recent papers suggest that a genetic analysis of trichome morphogenesis may yield insight into the role of the cytoskeleton during cellular morphogenesis. In particular, it is found that filamentous actin (F-actin) plays an important role during Arabidopsis trichome development. Specific rearrangements of the actin cytoskeleton occur during the development of the mature trichome cell. F-actin-disrupting drugs do not affect the establishment of polarity during trichome development; however, the maintenance and coordination of the normal pattern of cell growth are very sensitive to the same agents. In contrast, inhibitors that depolymerize microtubules severely inhibit cell polarization. Disruption of the actin cytoskeleton in growing trichomes phenocopies a class of mutations that cause a distorted trichome morphology. An analysis of cell shape and microfilament structure in wild-type, mutant, and drugtreated trichomes is consistent with a role for actin microfilaments in the maintenance and co-ordination of an established growth pattern during Arabidopsis trichome formation. 1. GENETIC ANALYSIS OF THE PLANT CYTOSKELETON The actin cytoskeleton comprises an intricate filamentous network that is essential for the trafficking of organelles and vesicles in eukaryotic cells. This transport activity is thought to be necessary for the normal growth of many