An analysis of the NET1 proteins: a group of novel plant actin-binding proteins

Abstract

The NET protein superfamily is a recently discovered family of novel, plant-specific actin binding proteins. The identification of this family represents a significant discovery as the plant cytoskeleton is not identical to the animal cytoskeleton and plant cells show plant specific processes and subcellular structures which rely on actin. There is a need for plant specific proteins which are capable of modelling actin within plant cells.

The NET family comprises thirteen proteins in Arabidopsis thaliana, which share the NET actin binding domain (found at the N-terminal end of each protein). Based on the C-terminal domains of the proteins, the family can be separated into four groups, each with a particular localisation. The localisations of these proteins are frequently within plant specific cell types, such as pollen tubes, guard cells or roots, or to plant specific cell structures such as plasmodesmata. It is thought that these proteins may be involved in modelling the actin cytoskeleton at junctions between actin and membranes (either cell membranes or membrane bound structures such as the endoplasmic reticulum).

The NET1 proteins are a group of four proteins, each consisting of an N-terminal actin binding domain and C-terminal coiled-coil domains. NET1a was the first protein to be discovered in a high-throughput screen of plant proteins for novel localisations carried out by Karl Oparka, where it was shown to bind to filaments. Work by Calcutt (Calcutt 2009) showed the filaments to be the actin cytoskeleton.

The aim of this thesis has been to complete the characterisation of all Group 1 NET proteins, building on the analysis of NET1a by Calcutt (Calcutt 2009) and to investigate the possible functions of the NET1 subfamily proteins. All four proteins have been shown to be capable of actin binding and to be expressed in, and locate to structures within, the roots of A. thaliana. NET1a has been linked to plasmodesmata, and the combined absence of NET1a and NET1b in the plant results in a cumulative, long root phenotype. Theories to explain this phenotype are suggested here, although the validation and testing of these will form the basis of future work.