Actin control over microtubules suggested by DISTORTED2 encoding the Arabidopsis ARPC2 subunit homolog

Abstract

In Arabidopsis, based on the randomly misshapen phenotype of leaf epidermal trichomes, eight genes have been grouped into a 'DISTORTED' class. Three of the DIS genes, WURM, DISTORTED1 and CROOKED have been cloned recently and encode the ARP2, ARP3 and ARPC5 subunits respectively, of a conserved actin modulating ARP2/3 complex. Here we identify a fourth gene, DISTORTED2 as the Arabidopsis homolog of the ARPC2 subunit of the ARP2/3 complex. Like other mutants in the complex dis2 trichomes also display supernumerary, randomly localized cortical actin patches. In addition dis2 trichomes possess abnormally clustered endoplasmic microtubules near sites of actin aggregation. Since microtubules are strongly implicated in the establishment and maintenance of growth directionality in higher plants our observations of aberrant microtubule clustering in dis2 trichomes suggests a convincing explanation for the randomly distorted trichome phenotype in dis mutants. In addition, the close proximity of microtubule clusters to the arbitrarily dispersed cortical actin patches in the dis mutants provides fresh insights into cytoskeletal interactions leading us to suggest that in higher plants microtubule arrangements directed towards the establishment and maintenance of polar growth-directionality are guided by cortical actin behavior and organization.