TCO, a Putative Transcriptional Regulator in , Is a Target of the Protein Kinase CK2.

As multicellular organisms grow, spatial and temporal patterns of gene expression are strictly regulated to ensure that developmental programs are invoked at appropriate stages. In this work, we describe a putative transcriptional regulator in , TACO LEAF (TCO), whose overexpression results in the ectopic activation of reproductive genes during vegetative growth. Isolated as an activation-tagged allele, displays gene misexpression and phenotypic abnormalities, such as curled leaves and early flowering, characteristic of chromatin regulatory mutants.

HISTONE DEACETYLASE 19 and the flowering time gene FD maintain reproductive meristem identity in an age-dependent manner.

The shoot apical meristem (SAM) undergoes developmental transitions that include a shift from vegetative to reproductive growth. This transition is triggered by flowering time genes, which up-regulate floral meristem (FM) identity genes that, in turn, control flower development by activating floral organ identity genes. This cascade of transcriptional activation is refined by repression mechanisms that temporally and spatially restrict gene expression to ensure proper development.

Spatial Auxin Signaling Controls Leaf Flattening in Arabidopsis.

The flattening of leaves to form broad blades is an important adaptation that maximizes photosynthesis. However, the molecular mechanism underlying this process remains unclear. The WUSCHEL-RELATED HOMEOBOX (WOX) genes WOX1 and PRS are expressed in the leaf marginal domain to enable leaf flattening, but the nature of WOX expression establishment remains elusive.

The role of AUXIN RESPONSE FACTORs in the development and differential growth of inflorescence stems.

Plants react to environmental cues by altering their growth and development, which can include organ tropic responses. These differential growth responses are triggered by the hormone auxin, and AUXIN RESPONSE FACTORs (ARFs) have been implicated in numerous organ tropisms in Arabidopsis thaliana. Surprisingly, despite being critical for light capture and overall plant morphology, inflorescence stem tropic responses remain relatively understudied, with presumed direct links to ARF function yet to be established.

The auxin response factor MONOPTEROS controls meristem function and organogenesis in both the shoot and root through the direct regulation of PIN genes.

The regulatory effect auxin has on its own transport is critical in numerous self-organizing plant patterning processes. However, our understanding of the molecular mechanisms linking auxin signal transduction and auxin transport is still fragmentary, and important regulatory genes remain to be identified. To track a key link between auxin signaling and auxin transport in development, we established an Arabidopsis thaliana genetic background in which fundamental patterning processes in both shoot and root were essentially abolished and the expression of PIN FORMED (PIN) auxin efflux facilitators was dramatically reduced.

The identification and characterization of specific ARF-Aux/IAA regulatory modules in plant growth and development.

The current model of auxin-inducible transcription describes numerous regulatory interactions between AUXIN RESPONSE FACTORs (ARFs) and Aux/IAAs. However, specific relationships between individual members of these families in planta remain largely uncharacterized. Using a systems biology approach, the entire suite of Aux/IAA genes directly regulated by the developmentally pivotal ARF MONOPTEROS (MP) was recently determined for multiple Arabidopsis tissue types.

Distinct subclades of Aux/IAA genes are direct targets of ARF5/MP transcriptional regulation.

The regulatory interactions between AUXIN RESPONSE FACTORS (ARFs) and Aux/IAA repressors play a central role in auxin signal transduction. Yet, the systems properties of this regulatory network are not well established. We generated a steroid-inducible ARF5/MONOPTEROS (MP) transgenic background to survey the involvement of this factor in the transcriptional regulation of the entire Aux/IAA family in Arabidopsis thaliana.

Transcriptional regulation of LUX by CBF1 mediates cold input to the circadian clock in Arabidopsis.

Circadian clocks allow organisms to anticipate daily changes in the environment to enhance overall fitness. Transcription factors (TFs) play a prominent role in the molecular mechanism but are incompletely described possibly due to functional redundancy, gene family proliferation, and/or lack of context-specific assays. To overcome these, we performed a high-throughput yeast one-hybrid screen using the LUX ARRYHTHMO (LUX) gene promoter as bait against an Arabidopsis TF library.

A dominant mutation reveals asymmetry in MP/ARF5 function along the adaxial-abaxial axis of shoot lateral organs.

The establishment of adaxial-abaxial polarity in plant lateral organs involves elaborate interactions between members of several transcription factor families, including the Auxin Response Factors (ARFs). We previously described a dominant allele of ARF5/MONOPTEROS (MP), termed MPΔ, which causes severe vascular hypertrophy in shoot lateral organs. Here we report that these organs are also disrupted in adaxial-abaxial polarity.

Deletion of MP/ARF5 domains III and IV reveals a requirement for Aux/IAA regulation in Arabidopsis leaf vascular patterning.

Combinatorial interactions of AUXIN RESPONSE FACTORs (ARFs) and auxin/indole acetic acid (Aux/IAA) proteins through their common domains III and IV regulate auxin responses, but insight into the functions of individual proteins is still limited. As a new tool to explore this regulatory network, we generated a gain-of-function ARF genotype by eliminating domains III and IV from the functionally well-characterized ARF MONOPTEROS(MP)/ARF5. This truncated version of MP, termed MPΔ, conferred complementing MP activity, but also displayed a number of semi-dominant traits affecting auxin signaling and organ patterning.

Spatio-temporal sequence of cross-regulatory events in root meristem growth.

A central question in developmental biology is how multicellular organisms coordinate cell division and differentiation to determine organ size. In Arabidopsis roots, this balance is controlled by cytokinin-induced expression of SHORT HYPOCOTYL 2 (SHY2) in the so-called transition zone of the meristem, where SHY2 negatively regulates auxin response factors (ARFs) by protein-protein interaction. The resulting down-regulation of PIN-FORMED (PIN) auxin efflux carriers is considered the key event in promoting differentiation of meristematic cells.

Why so repressed? Turning off transcription during plant growth and development.

To ensure correct patterns of gene expression, eukaryotes use a variety of strategies to repress transcription. The transcriptional regulators mediating this repression can be broadly categorized as either passive or active repressors. While passive repressors rely on mechanisms such as steric hindrance of transcriptional activators to repress gene expression, active repressors display inherent repressive abilities commonly conferred by discrete repression domains.

AMP1 and MP antagonistically regulate embryo and meristem development in Arabidopsis.

AUXIN RESPONSE FACTOR (ARF)-mediated signaling conveys positional information during embryonic and postembryonic organogenesis and mutations in MONOPTEROS (MP/ARF5) result in severe patterning defects during embryonic and postembryonic development. Here we show that MP patterning activity is largely dispensable when the presumptive carboxypeptidase ALTERED MERISTEM PROGRAM 1 (AMP1) is not functional, indicating that MP is primarily necessary to counteract AMP1 activity. Closer inspection of the single and double mutant phenotypes reveals antagonistic influences of both genes on meristematic activities throughout the Arabidopsis life cycle.

Investigating the in vivo activity of the DeaD protein using protein-protein interactions and the translational activity of structured chloramphenicol acetyltransferase mRNAs.

Here, we report the use of an in vivo protein-protein interaction detection approach together with focused follow-up experiments to study the function of the DeaD protein in Escherichia coli. In this method, functions are assigned to proteins based on the interactions they make with others in the living cell. The assigned functions are further confirmed using follow-up experiments.

Auxin signals--turning genes on and turning cells around.

The extremely wide spectrum of the plant processes that are influenced by auxin raises the question of how signals conveyed by a single molecule can trigger such a variety of responses. Although many aspects of auxin function remain elusive, others have become genetically tractable. The identification of crucial genes in auxin signal transduction and auxin transport in the past few years has led to molecularly testable concepts of how auxin signals regulate gene activities in individual cells, and how the polar transport of auxin could impact on patterning processes throughout the plant.