Root Epidermal Cell Patterning Is Modulated by a Critical Residue in the WEREWOLF Transcription Factor.

The Arabidopsis (Arabidopsis thaliana) root epidermis exhibits a position-dependent pattern of root-hair and nonhair cell types. A highly orchestrated network of gene regulatory interactions, including the R2R3-type MYB transcription factor WEREWOLF (WER), is responsible for generating this cell pattern during root development. In this study, we identified a novel wer mutant from a genetic enhancer screen, designated wer-4, that exhibits an abnormal pattern of root-hair and nonhair cells. We established that wer-4 bears a single-residue substitution (D105N) in the DNA-binding R3 MYB repeat of WER, which differentially affects the transcription of WER target genes, including GLABRA2, CAPRICE, TRIPTYCHON, and ENHANCER OF TRY AND CPC1 This modulation of the gene regulatory network leads to altered levels and distributions of cell fate regulators in the differentiating epidermal cells that ultimately generate the abnormal cell-type pattern. We also created several WER variants with substitutions at the Asp-105 position, and these exhibited a variety of gene expression and cell-type pattern alterations, further supporting the critical role of this residue. These findings provide insight into WER protein function and its importance in generating the proper balance of downstream transcriptional factors in the gene regulatory network that establishes root epidermal cell fate.