Biology subjects

Schrick, K.

Publications and source records attributed to Schrick, K..

6 recordsLinked to original sources

bioRxiv2026

GLABRA2 regulates gene expression via its own EAR-motif mediated recruitment of the TPL/TPR corepressors

The Arabidopsis HD-Zip IV transcription factor GLABRA2 (GL2) displays dual regulatory capabilities, as an activator and repressor of genes that mediate cell-type differentiation of the epidermis. GL2 binds L1 box elements in the promoters of its target genes; however, the mechanisms by which it controls gene expression remain elusive. GL2 contains two putative ethylene-responsive element-binding factor-associated amphiphilic repression (EAR) motifs proximal to its N- and C-termini. The N-terminal EAR motif is highly conserved among GL2 orthologs that form a distinct clade of HD-Zip IV transcription factors in monocots and dicots. We demonstrate that deletion or Ala substitution of this N-terminal EAR motif results in a partial loss-of-function phenotypes in trichomes, non-hair root cells, and seed coat mucilage. In contrast, mutations affecting the C-terminal EAR motif display improper nuclear localization, likely due to protein misfolding. Yeast two-hybrid and in planta co-immunoprecipitation assays show that GL2 selectively interacts with the TOPLESS (TPL) and TPL-RELATED (TPR) corepressors via its N-terminal EAR motif. Fusion of the SUPERMAN REPRESSIVE DOMAIN X (SRDX) with the gl2 N-terminal EAR motif mutant (gl2EAR-N) rescues the epidermal defects of gl2 mutants. Transcriptome analysis of mutant and wild-type seedling roots further confirms the role of the GL2 N-terminal EAR motif in tuning gene expression. Our findings support a model whereby GL2 recruits TPL/TPR corepressors via its EAR motif to sequester histone-modifying proteins, resulting in chromatin remodeling required for epidermal development.

plant biology↗

bioRxiv2026

ATML1-GIR1-TPL/TPR transcriptional repression module controls glucosinolates and giant cells in Arabidopsis thaliana sepals

Glucosinolates (GSLs) are sulfur- and nitrogen-containing secondary metabolites that serve as defense compounds in Arabidopsis and other members of the Brassicales. Although the enzymatic pathway that produces GSLs is well-studied, the upstream mechanisms that control their tissue-specific synthesis are poorly understood. We identified a novel repression module that transcriptionally regulates GSL levels in sepals, the modified leaves that protect reproductive tissues within the floral bud. GLABRA2 (GL2) INTERACTING REPRESSOR1 (GIR1) interacts directly with Arabidopsis thaliana MERISTEM LAYER1 (ATML1), an HD-Zip IV transcription factor known to be required for giant cell formation in the sepal epidermis. This interaction requires a predicted Zn finger of GIR1 and the C-terminal START adjacent domain (STAD) of ATML1. The gir1 loss-of-function mutants exhibit excess giant cells, in contrast to atml1 mutants which display fewer giant cells, supporting the role of GIR1 as a negative regulator of ATML1. We confirmed that GIR1 interacts with TOPLESS (TPL) and TOPLESS-RELATED (TPR) corepressors, and coimmunoprecipitation demonstrated that GIR1 acts as an adaptor protein connecting ATML1 and TPL/TPR. RNA sequencing revealed that numerous genes involved in GSL biosynthesis, including the key transcriptional regulator MYB29, are upregulated in gir1 mutants. Consistent with the transcriptomic data, chemical analysis revealed that gir1 mutants display elevated GSL levels in sepals. Mass spectrometry imaging confirmed high GSL accumulation in gir1 sepals compared to wild type and atml1. Overall, our findings uncover a previously unrecognized link between cell expansion and GSL metabolism, suggesting strategies for engineering plants with cell-type specific GSL profiles. Significance StatementPlants belonging to the order Brassicales produce sulfur-containing glucosinolate (GSL) metabolites that serve in defense against herbivory. In cruciferous vegetables such as broccoli and kale, these compounds contribute to their unique flavors and health-promoting attributes. In agriculturally important oilseed crops, they affect the palatability of animal feeds. Here, we identified a novel transcriptional regulatory module that controls GSL biosynthesis in the epidermis of the sepal, the floral organ that protects the reproductive tissues. This regulatory module also controls cell expansion of specific cell types in the sepal, demonstrating a surprising connection between cell growth and a chemical defense pathway in plants. Our results suggest strategies for engineering crops with tissue-specific GSL profiles to fit agronomic needs.

plant biology↗

bioRxiv2024

The transcription factor ATML1 maintains giant cell identity by inducing synthesis of its own (very) long-chain fatty acid-containing ligands

During development, cells not only adopt specialized identities but also maintain those identities. Endoreduplication is thought to maintain cell identity. High concentrations of ARABIDOPSIS THALIANA MERISTEM LAYER1 (ATML1) specify giant cell identity and induce endoreduplication in sepals. How different concentrations of ATML1 can specify different identities remains unclear. Here, we show that high concentrations of ATML1 induce the biosynthesis of both long-chain and very long-chain fatty acids (LCFAs/VLCFAs), and these fatty acids are required for the maintenance of giant cell identity. Inhibition of VLCFA biosynthesis causes endoreduplicated giant cells to resume division and lose their identity, indicating that endoreduplication is not sufficient to maintain cell identity. Structural predictions suggest that LCFA-containing lipids bind to the START domain 2 of ATML1, causing ATML1 dimerization and its auto-activation. Our data and modeling imply that ATML1 induces biosynthesis of its own lipid ligands in a positive feedback loop, shedding light on the intricate network dynamics that specify and maintain giant cell identity. Teaser: Endoreduplicated cells in Arabidopsis thaliana sepals divide and de-differentiate in the absence of VLCFA biosynthesis.

plant biology↗

bioRxiv2023

Nuclear localization of HD-Zip IV transcription factor GLABRA2 is driven byImportin α

GLABRA2 (GL2), a class IV homeodomain leucine-zipper (HD-Zip IV) transcription factor (TF) from Arabidopsis, is a developmental regulator of specialized cell types in the epidermis. GL2 contains a putative monopartite nuclear localization sequence (NLS) partially overlapping with its homeodomain (HD). We demonstrate that NLS deletion or alanine substitution of its basic residues (KRKRKK) affects nuclear localization and results in a loss-of-function phenotype. Fusion of the predicted NLS (GTNKRKRKKYHRH) to the fluorescent protein EYFP is sufficient for its nuclear localization in roots and trichomes. The functional NLS is evolutionarily conserved in a distinct subset of HD-Zip IV members including PROTODERMAL FACTOR2 (PDF2). Despite partial overlap of the NLS with the HD, genetic dissection of the NLS from PDF2 indicates that nuclear localization and DNA binding are separable functions. Affinity purification of GL2 from plant tissues followed by mass spectrometry-based proteomics identified Importin (IMP) isoforms as potential GL2 interactors. NLS structural prediction and molecular docking studies with IMP-3 revealed major interacting residues. Split-ubiquitin cytosolic yeast two-hybrid assays suggest interaction between GL2 and four IMP isoforms from Arabidopsis. Direct interactions were verified in vitro by co-immunoprecipitation with recombinant proteins. IMP triple mutants (imp- 1,2,3) exhibit defects in EYFP:GL2 nuclear localization in trichomes but not in roots, consistent with tissue-specific and redundant functions of IMP isoforms in Arabidopsis. Taken together, our findings provide mechanistic evidence for IMP-dependent nuclear localization of GL2 and other HD-Zip IV TFs in plants. One sentence summaryGLABRA2, a representative HD-Zip IV transcription factor from Arabidopsis, contains an evolutionarily conserved monopartite nuclear localization sequence that is recognized by Importin for translocation to the nucleus, a process that is necessary for cell-type differentiation of the epidermis.

plant biology↗

bioRxiv2021

START domain mediates Arabidopsis GLABRA2 transcription factor dimerization and turnover independently of homeodomain DNA binding

Class IV homeodomain leucine-zipper transcription factors (HD-Zip IV TFs) are key regulators of epidermal differentiation that are characterized by a DNA-binding homeodomain (HD) in conjunction with a lipid-binding domain termed START (Steroidogenic Acute Regulatory (StAR)-related lipid Transfer). Previous work established that the START domain of GLABRA2 (GL2), a HD-Zip IV member from Arabidopsis, is required for transcription factor activity. Here, we address the functions and possible interactions of START and the HD in DNA binding, dimerization, and protein turnover. Deletion analysis of the HD and missense mutations of a conserved lysine (K146) result in phenotypic defects in leaf trichomes, root hairs and seed mucilage, similar to those observed for START domain mutants, despite nuclear localization of the respective proteins. In vitro and in vivo experiments demonstrate that while HD mutations impair binding to target DNA, the START domain is dispensable for DNA binding. Vice versa, protein interaction assays reveal impaired GL2 dimerization for multiple alleles of START mutants, but not HD mutants. Using in vivo cycloheximide chase experiments, we provide evidence for the role of START, but not HD, in maintaining protein stability. This work advances our mechanistic understanding of HD-Zip TFs as multidomain regulators of epidermal development in plants.

plant biology↗

bioRxiv2021

Arabidopsis PROTODERMAL FACTOR2 binds lysophosphatidylcholines and transcriptionally regulates phospholipid metabolism

Plant homeodomain leucine-zipper IV (HD-Zip IV) transcription factors (TFs) contain an evolutionarily conserved steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domain. The START domain is required for TF activity; however, its presumed role as a lipid sensor is not well understood. Here we used tandem affinity purification from Arabidopsis cell cultures to demonstrate that PROTODERMAL FACTOR2 (PDF2), a representative family member which controls epidermal differentiation, recruits lysophosphatidylcholines in a START-dependent manner. In vitro assays with recombinant protein verified that a missense mutation in a predicted ligand contact site reduces lysophospholipid binding. We additionally uncovered that PDF2 controls the expression of phospholipid-related target genes by binding to a palindromic octamer with consensus to a phosphate (Pi) response element. Phospholipid homeostasis and elongation growth were altered in pdf2 mutants according to Pi availability. Cycloheximide chase experiments further revealed a role for START in maintaining protein levels, and Pi limitation resulted in enhanced protein destabilization, suggesting a mechanism by which lipid binding controls TF activity. We propose that the START domain serves as a molecular sensor for membrane phospholipid status in the epidermis. Overall our data provide insights towards understanding how the lipid metabolome integrates Pi availability with gene expression.

plant biology↗