Regulation of root epidermal cell fate specification in Arabidopsis.

摘要

The formation of the root epidermis in Arabidopsis provides a simple and elegant model for the study of cell fate specification. An epidermal cell develops as a root hair cell when it overlies two cortical cells, and develops as a root non-hair cell when it overlies a single cortical cell. A network of transcription factor proteins, WEREWOLF (WER), GLABRA3 (EGL3), ENHANCER OF GLABRA3 (EGL3), and TRANSPARENT TESTA GLABRA1 (TTG1), promote the non-hair cell fate through the activation of GLABRA2 (GL2) gene expression in the non-hair cell position, and promote the hair cell fate through the activation of CAPRICE (CPC) gene expression in the non-hair cell position. The CPC protein acts through a mechanism of lateral inhibition to regulate gene expression in the neighboring hair cells by the direct movement of the CPC protein from non-hair cells to hair cells and throughout the epidermis. We have identified four CPC homologs, TRIPTYCHON (TRY), ENHANCER OF TRY AND CPC 1, 2 and 3 (ETC1, ETC2 and ETC3), that are able to functionally substitute for the CPC in root epidermal patterning. CPC, TRY and ETC1 are expressed in the non-hair cell position and act in a partially redundant manner to regulate cell fate specification in the root, whereas ETC2 and ETC3 are not expressed in the root and do not have a role in root epidermal patterning. We identify a new regulator of root epidermal patterning, TRANSPARENT TESTA GLABRA2 (TTG2), that enhances a cpc mutant phenotype. We find that the TTG2 and GL2 and genes positively regulate TRY gene expression, but do not regulate CPC or ETC1 gene expression in the non-hair cell position. Thus, we propose that TTG2 and GL2 act in a secondary step to initiate and maintain lateral inhibition signaling through the regulation of TRY gene expression in the root epidermis.