A generalized method for transfecting root epidermis uncovers endosomal dynamics in Arabidopsis root hairs

Progress in analysing the cellular functions of many structural proteins has accelerated through the use of confocal microscopy together with transient gene expression. Several methods for transient expression have been developed in the past few years, but their application has seen limited success beyond a few tractable species and tissues. We have developed a simple and efficient method to visualize fluorescent proteins in Arabidopsis root epidermis using co-cultivation of seedlings with Agrobacterium rhizogenes. The method is equally suitable for transient gene expression in other species, including Thellungiella, and can be combined with supporting molecular and biochemical analyses. The method promises significant advantages for study of membrane dynamics, cellular development and polar growth in root hairs without interference in the development of the plant. Since the method targets specifically the root epidermis, it also offers a powerful tool to approach issues of root-rhizosphere interactions, such as ion transport and nutrient acquisition. As a proof of principle, we carried out transfections with fluorescent markers for the plasma membrane (NpPMA2-GFP, Nicotiana plumbaginifolia L. Plasma Membrane H+-ATPase 2), the endoplasmic reticulum (YFP-HDEL), and the Golgi apparatus (sialyl transferase-GFP) to trace their distribution in growing Arabidopsis root hairs and epidermis. The results demonstrate that, in Arabidopsis root hairs, movement of the Golgi is faster than previously reported for tobacco leaf epidermal cells, consistent with the high secretory dynamics of the tip growing cell; they show a pattern to the endoplasmic reticulum within the cytoplasm that is more diffuse than found in tobacco leaf epidermis, and they confirm previous findings of a polarized distribution of the endoplasmic reticulum at the tip of growing root hairs.