MYB23 Localizes to the Nucleus of N-Position Epidermal Cells As a predicted transcription factor protein produced from N cell– specific transcripts, MYB23 may be expected to localize and act within the nucleus of cells in the N position of the root epidermis. On the other hand, some transcription factors participating in root epidermal cell specification (e.g., CPC and GL3) are able to move from cell to cell (Bernhardt et al., 2005; Kurata et al., 2005). To define the location of the MYB23 protein, we generated and analyzed a transgenic line bearing an in-frame MYB23-GFP (for green fluorescent protein) reporter translational fusion (PMYB23: MYB23-GFP) (Figure 3A). This transgene was expressed under the control of MYB23 regulatory sequences (3.1-kb 59 flanking DNA fragment and 1.0-kb 39 flanking DNA fragment) previously determined to be sufficient in genomic complementation experiments to rescue the trichome-branching defect in the myb23 mutant (Kirik et al., 2005). We found that this translational fusion was able to rescue the branching defect in the myb23 mutant trichomes (Figure 3B), indicating that the MYB23-GFP protein functions like the native MYB23 in Arabidopsis. Analysis of the PMYB23:MYB23-GFP plants showed that GFP fluorescence was present in the nucleus of the developing root epidermal cells located in the N position (Figure 3C). As a negative control, we generated a GFP transcriptional fusion driven by the same regulatory sequences that were used for the PMYB23:MYB23-GFP construction (PMYB23: GFP), which exhibited fluorescence generally distributed throughout the cells (Figure 3C). This overall distribution seems to be caused by the nonspecific diffusion of the GFP, which is expressed in the N-position cells, based on the fact that the fluorescent signal from the endoplasmic reticulum (ER)–targeted GFP driven by the same regulatory sequences is found only in the N-position cells (Figure 3C, inset). These results indicate that the MYB23 protein accumulates in the nuclei of the developing non-hair cells and does not move from cell to cell.