Meagher Laboratory

Ectopic expression of late pollen actin ACT1 protein in leaves from a vegetative ACT2 promoter dramataicaly disrupts the cytoskeleton and reveals that there are distinct protein isovariant differences. Control plants overexpressing the ACT2 protein in leaves show little effect. The work proves the functional non-equivalency of at least two plant actin isovariants.

In a wild type Arabidopsis leaf mesophyll cell chloroplasts (red) are attached to F-actin filaments & bundles (green) positioned in the cell cortex. This attachement is essential to the streaming of chloroplants in the cytoplasm.

Ectopically expressed reproductive ACT1 protein is organized into bizaare actin filaments, bundles, and sheets in Arabidopsis leaf mesophyll cells. This is not observed for over-expressed ACT2. One model to explain this result is that actin binding proteins that can sequester the ACT2 protein isovariant do not bind the ACT1 isovariant properly. The Arabidopsis genome encodes nearly 200 actin binding proteins.
Kandasamy et al., 2002; Meagher et al., 1999a,b; Meagher & Fechheimer, 2002.