Functional Analysis of TIMID Protein Promoting the Root-Hair Elongation in Response to Touching Stimulus of the Root.

Abstract

It is important for root hairs to keep touching soil in order to uptake water and nutrients efficiently. In Arabidopsis grown on agar, root hairs become longer when the roots are apart from the agar surface.
In the timid (tmd) mutant, however, the root hairs became shorter in the air. The TMD gene encodes a GPI-anchored protein. When the cells expressing GFP:TMD fusion protein were plasmolyzed, GFP signal was observed in the outside of the plasma membrane at the root-hair tips as well as around the cell boundary. The TMD protein, which lacks C-terminal region and was expected to be secreted from the plasma membrane, was able to complement the tmd mutant. These results suggest that the TMD protein is released from plasma membrane in the root-hair tip, and regulates the root hair elongation in response to touching stimulus.