Amino acid substitution in CAPRICE (CPC) protein affects its cell-to-cell movement in the root epidermis of Arabidopsis thaliana

CAPRICE (CPC), a single-repeat R3-type MYB transcription factor, regulates root hair formation by transferring from non-root hair cells to root hair cells. The CPC homologue protein ENHANCER OF TRY AND CPC1 (ETC1) does not move between the cells in the root epidermis. To understand which region of the CPC is involved in cell-to-cell movement, three types of chimeric constructs (chimaeras 6, 7, and 8) were generated by replacing specific amino acids of ETC1, and transforming them into wild-type Arabidopsis thaliana (Col-0). The root phenotypes, root hair and trichome numbers, and location of the CPC protein in each transgenic plant were investigated. Our previous study indicated that transgenic plants expressing CPC::CPC:2 × GFP and CPC:ETC1:2 × GFP had more root hair than Col-0. Compared to CPC::CPC:2 × GFP and CPC:ETC1:2 × GFP, the chimeras 6 and 7 had similar root hair numbers and GFP localizations. However, the chimera 8 had lower root hair numbers and chimera 8:GFP fusion proteins exhibited no fluorescence in some cells. These results suggest that the two amino acids substituted in chimeras 6 and 7 did not affect cell-to-cell movement ability; however, replacing the 24th cysteine of CPC with serine at the 20th position of ETC1 (chimera 8) could influence the root hair formation and cell-to-cell movement translocation of CPC. Our results provide insights into which amino acids in CPC may contribute to the difference in cell-to-cell movement ability. Elucidating the mechanism of cell-to-cell transfer of CPCs will lead to a better understanding of epidermal cell differentiation in plants.