The bHLH genes GLABRA3 (GL3) and ENHANCER OF GLABRA3 (EGL3) specify epidermal cell fate in the Arabidopsis root.
The position-dependent specification of the hair and non-hair cell types in the Arabidopsis root epidermis provides a simple model for the study of cell fate determination in plants. Several putative transcriptional regulators are known to influence this cell fate decision. Indirect evidence from studies with the maize R gene has been used to suggest that a bHLH transcription factor also participates in this process. We show that two Arabidopsis genes encoding bHLH proteins, GLABRA3 (GL3) and ENHANCER OF GLABRA3 (EGL3), act in a partially redundant manner to specify root epidermal cell fates. Plants homozygous for mutations in both genes fail to specify the non-hair cell type, whereas plants overexpressing either gene produce ectopic non-hair cells. We also find that these genes are required for appropriate transcription of the non-hair specification gene GL2 and the hair cell specification gene CPC, showing that GL3 and EGL3 influence both epidermal cell fates. Furthermore, we show that these bHLH proteins require a functional WER MYB protein for their action, and they physically interact with WER and CPC in the yeast two-hybrid assay. These results suggest a model in which GL3 and EGL3 act together with WER in the N cell position to promote the non-hair cell fate, whereas they interact with the incomplete MYB protein CPC in the H position, which blocks the non-hair pathway and leads to the hair cell fate.
Bernhardt
Christine
C
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 830 North University Avenue, Ann Arbor, MI 48109, USA.
Lee
Myeong Min
MM
Gonzalez
Antonio
A
Zhang
Fan
F
Lloyd
Alan
A
Schiefelbein
John
J
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics*; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D018257:Helix-Loop-Helix Motifs; D018517:Plant Roots / Q000235:genetics* / Q000254:growth & development; D030821:Plants, Genetically Modified / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D002352:Carrier Proteins; D018749:RNA, Plant; D014157:Transcription Factors; C417284:GL3 protein, Arabidopsis