Plant Physiol, February 2003, Vol. 131, pp. 643-655

The Arabidopsis STICHEL Gene Is a Regulator of Trichome Branch Number and Encodes a Novel Protein¹

Zentrum für Molekularbiologie Pflanzen, Entwicklungsgenetik, Universität Tübingen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany (H.I., D.B., A.S., B.S., G.J., M.H.); University of Köln, Botanical Institute III, Gyrhofstrasse 15, 50931 Köln, Germany (J.M., V.K., M.H.); and Rockefeller University, 1230 York Avenue, New York, New York 10021 (N.-H.C.)

Here, we analyze the STICHEL (STI) gene, which plays an important role in the regulation of branch number of the unicellular trichomes in Arabidopsis. We have isolated the STI locus by positional cloning and confirmed the identity by sequencing seven independent sti alleles. The STI gene encodes a protein of 1,218 amino acid residues containing a domain with sequence similarity to the ATP-binding eubacterial DNA-polymerase III -subunits. Because endoreduplication was found to be normal in sti mutants the molecular function of STI in cell morphogenesis is not linked to DNA replication and, therefore, postulated to represent a novel pathway. Northern-blot analysis shows that STI is expressed in all organs suggesting that STI function is not trichome specific. The analysis of sti alleles and transgenic lines overexpressing STI suggests that STI regulates branching in a dosage-dependent manner.