The role of adenylate cyclase-associated protein in higher plant development

Abstract

The Actin Cytoskeleton is essential for Eukaryotic life and is involved in a diverse range of cellular functions. Cyclase Associated Protein (CAP) was first identified in yeast as a regulator of the CYR1 Adenylate Cyclase. Subsequently CAP family members have been identified in every Eukaryotic kingdom and have also been implicated in the regulation of Actin dynamics. It has been proposed that the CAP family promotes the recycling of Actin monomers by cooperating with members of the Profilin and Actin Depolymerising Factor families. This study represents an attempt to investigate the function and developmental role of AtCAP1, an Arabidopsis member of the CAP family. Arabidopsis thaliana is widely used as a model for higher plant development due to its small sequenced genome and the availability of a wide variety of mutants. The elimination of AtCAP1 expression results in a distinct developmental phenotype. Early characteristics include the absence of the root hair collar, reduced root hair initiation and extension. Later onset phenotypes include reduced plant height and a severe reduction in pollen viability. In vivo studies of the CAP-deficient cytoskeleton reveal a distinct loss of fine filamentous Actin and the appearance of dense Actin aggregates. Cell expansion is also significantly reduced. The interaction between AtCAP1 and F-Actin is demonstrated in vitro by a biochemical interaction study and a filament bundling activity is suggested. The multimerisation of AtCAP1 and its interaction with other components of the Actin Cytoskeleton are demonstrated via Yeast Two Hybrid interactions. It is concluded that AtCAP1 is essential for the organisation of the plant cells F-Actin network and that this in turn is required for correct growth and development. It is hypothesised that AtCAP1 function is mediated by regulating the interaction between F-Actin and other Actin-interacting proteins.