Characterization of three novel members of the Arabidopsis SHAGGY-related protein kinase (ASK) multigene family

In this paper we report the characterization of three novel members of the Arabidopsis shaggy-related protein kinase (ASK) multigene family, named ASK dzeta (ASK zeta), ASKetha (ASK eta) and ASKiota (ASK iota). The proteins en coded by the ASK genes share a highly conserved catalytic protein kinase do main and show about 70% identity to SHAGGY (SGG) and glycogen synthase kina se-3 (GSK-3) from Drosophila and rat respectively. SGG is an ubiquitous int racellular component of the wingless signalling pathway that establishes ce ll fate and/or pattern formation in Drosophila. At least ten different ASK genes are expected to be present per haploid genome of A. thaliana. Differe nt amino- and carboxy-terminal extensions distinguish different ASK family members. Five ASK gene sequences were analysed and shown to be present as s ingle-copy genes in the Arabidopsis genome. A comparison based on the highl y conserved catalytic domain sequences of all known sequences of the GSK-3 subfamily of protein kinases demonstrated a clear distinction between the p lant and the animal kinases. Furthermore, we established the presence of at least three distinct groups of plant homologues of SGG/GSK-3. These differ ent groups probably reflect biochemical and/or biological properties of the se kinases. The differential expression patterns of five ASK genes were acc essed by northern and in situ hybridization experiments using gene-specific probes. While ASK zeta is expressed in the whole embryo during its develop ment, ASK eta expression is limited to the suspensor cells. No signal was d etected for ASK alpha, ASK gamma and ASK iota in developing embryos.