Participation of the Arabidopsis bHLH Factor GL3 in Trichome Initiation Regulatory Events

Abstract

The development of trichomes (leaf hairs) from pluripotent epidermal cells in Arabidopsis (Arabidopsis thaliana) provides a powerful system to investigate the regulatory motifs involved in plant cell differentiation. We show here that trichome initiation is triggered within 4 h of the induction of the GLABRA3 (GL3) basic helix-loop-helix transcription factor. Within this developmental window, GL3 binds to the promoters of at least three genes previously implicated in the development and patterning of trichomes (GL2, CAPRICE, and ENHANCER OF TRIPTYCHON AND CAPRICE1) and activates their transcription. The in vivo binding of GL3 to the promoters of these genes requires the presence of the R2R3-MYB factor GL1, supporting a model in which a GL3-GL1 complex is part of the trichome initiation enhanceosome. In contrast, GL3 is recruited to its own promoter in a GL1-independent manner, and this results in decreased GL3 expression, suggesting the presence of a GL3 negative autoregulatory loop. In support of genetic analyses indicating that ENHANCER OF GL3 (EGL3) is partially redundant with GL3, we show that EGL3 shares some direct targets with GL3. However, our results suggest that GL3 and EGL3 work independently of each other. Taken together, our results provide a regulatory framework to understand early events of epidermal cell differentiation.

Jasmonic acid control of GLABRA3 links inducible defense and trichome patterning inArabidopsis

“…Previous studies have established that GL3 must interact with GL1 to be recruited to chromatin and regulate the expression of downstream genes to direct trichome development (Morohashi et al, 2007;Zhao et al, 2008). This is also true for induced trichome formation because gl1-S92F and urm23 (ttg1) mutants, both of which probably impair GL1-GL3 interaction, did not induce any trichomes after wounding or MeJA treatment.…”

A Single Amino Acid Substitution in IIIf Subfamily of Basic Helix-Loop-Helix Transcription Factor AtMYC1 Leads to Trichome and Root Hair Patterning Defects by Abolishing Its Interaction with Partner Proteins in Arabidopsis

“…AtMYC1 Is Required for Full GL2 Expression-We next focused on the epidermal cell determination defects in Atmyc1 mutants. To further explore the role of AtMYC1 in trichome and root hair determination, we examined the expression level of GL2 in Atmyc1, GL2 is a crucial transcription factor in trichome and non-hair cell development (16 -20), and it has been shown to be a direct target of the GL1-GL3-TTG1 complex (13,53). We, therefore, examined the expression level of GL2 in Atmyc1 by quantitative real-time PCR.…”

Arabidopsis VASCULAR-RELATED NAC-DOMAIN6 Directly Regulates the Genes That Govern Programmed Cell Death and Secondary Wall Formation during Xylem Differentiation

“…ChIP experiments were performed according to the method of Morohashi et al (2007). Cultured cells harboring estrogen-inducible VND6 treated with estrogen or DMSO for 24 h were fixed.…”