Differential Auxin-Transporting Activities of PIN-Formed Proteins in Arabidopsis Root Hair Cells

The document from May 3, 2010, details a study on the role of PIN-FORMED (PIN) proteins in auxin transport and root hair growth in Arabidopsis. Overexpression of PIN1, PIN2, PIN3, PIN4, PIN7, and PIN8 in root hair cells was found to inhibit root hair growth, with the degree of inhibition varying among the proteins. PIN8's efflux activity was newly demonstrated, and all these PINs were localized to the plasma membrane and formed internal compartments in response to brefeldin A. In contrast, PIN5 was localized mostly to internal compartments and slightly stimulated hair growth, suggesting it may enhance internal auxin availability. The study also showed that overexpression of PINs increased the length of root-hair-bearing epidermal cells and that different PINs have distinct auxin efflux activities. Treatment with an auxin efflux inhibitor or a trafficking inhibitor restored root hair growth in most PIN overexpressing lines, indicating the importance of cellular auxin levels for root hair growth. The study concluded that different PIN proteins have differential molecular activities and subcellular localizations, which affect auxin transport and root hair development in Arabidopsis.