Abstract
Leaf trichomes in Arabidopsis thaliana develop through several distinct cellular processes, such as patterning, differentiation, and growth. Although recent studies have identified several key transcription factors as regulating early patterning and differentiation steps, it is still largely unknown how these regulatory proteins mediate subsequent trichome development, which is accompanied by rapid cell growth and branching. Here, we report a novel trichome mutation in Arabidopsis, which in contrast with previously identified mutants, increases trichome cell size without altering its overall patterning or branching. We show that the corresponding gene encodes a GT-2-LIKE1 (GTL1) protein, a member of the trihelix transcription factor family. GTL1 is present within the nucleus during the postbranching stages of trichome development, and its loss of function leads to an increase in the nuclear DNA content only in trichomes that have completed branching. Our data further demonstrate that the gtl1 mutation modifies the expression of several cell cycle genes and partially rescues the ploidy defects in the cyclin-dependent kinase inhibitor mutant siamese. Taken together, this study provides the genetic evidence for the requirement of transcriptional regulation in the repression of ploidy-dependent plant cell growth as well as for an involvement of GTL trihelix proteins in this regulation.
Highlights
Plant trichomes are highly specialized epidermal cells implicated in several important functions, including transpiration control, freezing tolerance, and protection against insects, diseases, and UV light (Johnson, 1975; Mauricio and Rausher, 1997)
Recent studies have shown that five other single-repeat MYB homologs, CAPRICE (CPC), ENHANCER OF TRY AND CPC1 (ETC1), ETC2, ETC3/CPC-LIKE-MYB3, and TRICHOMELESS1 (TCL1), participate in trichome development, and all, except TCL1, which is required for the stem and pedicel trichome formation, act redundantly with TRY in leaf trichome initiation (Esch et al, 2004; Kirik et al, 2004a, 2004b; Schellmann et al, 2007; Wang et al, 2007; Tominaga et al, 2008; Wester et al, 2009)
We demonstrate that the corresponding gene encodes a plant-specific trihelix transcription factor, GT-2LIKE1 (GTL1), and that it functions as a negative regulator of ploidy-dependent cell growth during postbranching phases of trichome development
Summary
Plant trichomes are highly specialized epidermal cells implicated in several important functions, including transpiration control, freezing tolerance, and protection against insects, diseases, and UV light (Johnson, 1975; Mauricio and Rausher, 1997). Leaf trichomes in Arabidopsis thaliana develop through several distinct cellular processes, and over the last decade, they have become an ideal model system to study various developmental processes, such as cell patterning, differentiation, and morphogenesis, at the single cell level (Hulskamp et al, 1994). Recent studies have shown that five other single-repeat MYB homologs, CAPRICE (CPC), ENHANCER OF TRY AND CPC1 (ETC1), ETC2, ETC3/CPC-LIKE-MYB3, and TRICHOMELESS1 (TCL1), participate in trichome development, and all, except TCL1, which is required for the stem and pedicel trichome formation, act redundantly with TRY in leaf trichome initiation (Esch et al, 2004; Kirik et al, 2004a, 2004b; Schellmann et al, 2007; Wang et al, 2007; Tominaga et al, 2008; Wester et al, 2009)
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