Deletion analysis of AGD1 reveals domains crucial for plasma membrane recruitment and function in root hair polarity.

AGD1, a plant ACAP-type ADP-ribosylation factor-GTPase activating protein (ARF-GAP), functions in specifying root hair polarity in Arabidopsis thaliana To better understand how AGD1 modulates root hair growth, we generated full-length and domain-deleted AGD1-green fluorescent protein (GFP) constructs, and followed their localization during root hair development. AGD1-GFP localized to the cytoplasm and was recruited to specific regions of the root hair plasma membrane (PM). Distinct PM AGD1-GFP signal was first detected along the site of root hair bulge formation. The construct continued to mark the PM at the root hair apical dome, but only during periods of reduced growth. During rapid tip growth, AGD1-GFP labeled the PM of the lateral flanks and dissipated from the apical-most PM. Deletion analysis and a single domain GFP fusion revealed that the pleckstrin homology (PH) domain is the minimal unit required for recruitment of AGD1 to the PM. Our results indicate that differential recruitment of AGD1 to specific PM domains is an essential component of the membrane trafficking machinery that facilitates root hair developmental phase transitions and responses to changes in the root microenvironment.