Analysis of the Regulation of TTG1-dependent Pathways

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SummaryThe plant epidermis is the plant's environmental contact layer and, as such, is critical for controlling such processes as gas exchange, nutrient uptake, interactions with insects and disease organisms, and the transmission of light. The Arabidopsis protodermal cell differentiates into just a few epidermal cell types. On the primary root there are just two cell types, hair and non-hair. On the leaf there are three or four cell types, guard cell, trichome (and trichome subsidiary cell), and pavement cell. This proposal aims to study the processes and molecules that lead to epidermal cell fate decision events and control of the anthocyanin secondary metabolic pathway. The control of cell fate in the plant epidermis is a valuable model system for understanding plant developmental processes and eventually understanding how a plant interacts with its environment. The theme running through this proposal is to understand the processes that are dependent on a key WD-repeat-containing pleiotropic epidermal regulator, Transparent Testa Glabra 1 (TTG1). TTG1 controls such disparate epidermal pathways as shoot trichome and root hair differentiation, anthocyanin pigment production, and seed coat mucilage cell differentiation.Plants triple mutant for three basic-Helix-Loop-Helix loci, Glabra3, Enhancer of Glabra3, and TT8, phenocopy the ttg1 mutant. These proteins form protein-protein interactions with TTG1, with each other and with a series of myb elements. When overexpressed, these bHLH proteins can suppress the ttg1 mutation. Molecular, genetic and biochemical experiments are proposed to understand the function of the TTG1-associated complex.Specific goals for this proposal include: exploration of the differential roles for GL3, EGL3 and TT8 in trichome initiation and in activating the anthocyanin pathway; determination of whether the GL2 and DFR promoters are the direct targets of bHLH/myb transcription factors and test the hypothesis that promoter discrimination is at the myb level; continue the characterization of TTG1's role in controlling the activity of transcription complexes; and work towards identifying all members of TTG1-associated transcription complexes.Broader impactOne way this project will have a broader impact is that the information resulting from the research proposed here will increase our basic knowledge of the control of plant epidermal cell-fate decisions and plant secondary metabolism. Eventual uses of this knowledge include the ability to manipulate crops to make them better able to cope with diverse environments and to make them more nutritious for livestock and humans. Another impact will be that the original research provides opportunities for undergraduate, graduate and postdoctoral students to learn both technology and creative thinking. A third impact will be the felt by both Lloyd lab members and students from a local elementary and the Austin Community College (ACC). For the past six years, all lab members have participated in judging the yearly science fair at Barton Hills Elementary. This includes interactive interviews of the elementary students. For the past three years, the Lloyd lab has taught a lab section for the Biotechnology program at ACC. This section consists of the ACC students coming to UT to do a hands-on plant transformation and lab robotics experiments.