Abstract
Phosphoprotein-binding domains are found in many different proteins and specify protein-protein interactions critical for signal transduction pathways. Forkhead-associated (FHA) domains bind phosphothreonine and control many aspects of cell proliferation in yeast (Saccharomyces cerevisiae) and animal cells. The Arabidopsis (Arabidopsis thaliana) protein kinase-associated protein phosphatase includes a FHA domain that mediates interactions with receptor-like kinases, which in turn regulate a variety of signaling pathways involved in plant growth and pathogen responses. Screens for insertional mutations in other Arabidopsis FHA domain-containing genes identified a mutant with pleiotropic defects. dawdle (ddl) plants are developmentally delayed, produce defective roots, shoots, and flowers, and have reduced seed set. DDL is expressed in the root and shoot meristems and the reduced size of the root apical meristem in ddl plants suggests a role early in organ development.