Abstract: Profilin is an actin-binding protein that shows complex effects on the dynamics of the actin cytoskeleton. There are five profilin isoforms in Arabidopsis thaliana. However, it is still an open question whether these isoforms are functionally different. In present study, two profilin isoforms from Arabidopsis, PRF1 and PRF2 were fused with GFP tag and expressed in E. coli and Arabidopsis thaliana in order to compare their biochemical properties in vitro and their cellular distributions in vivo. Biochemical analysis revealed that fusion proteins of GFP-PRF1 and GFP-PRF2 can bind to poly-L-proline and G-actin showing remarkable differences. GFP-PRF1 has much higher affinities for both poly-L-proline and G-actin comparing to GFP-PRF2. Observations of living cells in stable transgenic Arabidopsis thaliana lines revealed that 35S::GFP-PRF1 formed a filamentous network, while 35S::GFP-PRF2 formed polygonal meshes. Results from the treatment with latrunculin A and subsequent recovery experiment indicated that filamentous alignment of GFP-PRF1 was likely associated with actin filaments. However, GFP-PRF2 localized to polygonal meshes resembling the endoplasmic reticulum. Our results provide evidence that Arabidopsis profilin isoforms PRF1 and PRF2 have different biochemical affinities for poly-L-proline and G-actin, and show distinctive localizations in living cells. These data suggest that PRF1 and PRF2 are functionally different isoforms.

Key words: profilin isoforms, PRF1, PRF2, actin filaments, endoplasmic reticulum;Arabidopsis