Role of TRIPTYCHON in trichome patterning in Arabidopsis

<p>Abstract</p> <p>Background</p> <p>Trichome patterning in <it>Arabidopsis thaliana </it>is governed by three types of activators, R2R3MYB, bHLH and WD40 proteins, and six R3MYB inhibitors. Among the inhibitors <it>TRIPTYCHON </it>(<it>TRY</it>) seems to fulfill a special function. Its corresponding mutants produce trichome clusters whereas all other inhibitors are involved in trichome density regulation.</p> <p>Results</p> <p>To better understand the role of <it>TRY </it>in trichome patterning we analyzed its transcriptional regulation. A promoter analysis identified the relevant regulatory region for trichome patterning. This essential region contains a fragment required for a double negative feedback loop such that it mediates the repression of <it>TRY</it>/<it>CPC </it>auto-repression. By transforming single cells of <it>pTRY</it>:GUS lines with <it>p35S</it>:<it>GL1, p35S</it>:<it>GL3 </it>and <it>p35S</it>:<it>TTG1 </it>in the presence or absence of <it>p35S</it>:<it>TRY </it>or <it>p35S</it>:<it>CPC </it>we demonstrate that TRY and CPC can suppress the <it>TRY </it>expression without the transcriptional down regulation of the activators. We further show by promoter/CDS swapping experiments for the R3MYB inhibitors TRY and CPC that the TRY protein has specific properties relevant in the context of both, cluster formation and trichome density.</p> <p>Conclusions</p> <p>Our identification of a <it>TRY </it>promoter fragment mediating a double negative feedback loop reveals new insight in the regulatory network of the trichome patterning machinery. In addition we show that the auto-repression by TRY can occur without a transcriptional down regulation of the activators, suggesting that the differential complex formation model has a biological significance. Finally we show that the unique role of TRY among the inhibitors is a property of the TRY protein.</p

Microtubule plus-ends reveal essential links between intracellular polarization and localized modulation of endocytosis during division-plane establishment in plant cells

BACKGROUND: A key event in plant morphogenesis is the establishment of a division plane. A plant-specific microtubular preprophase band (PPB) accurately predicts the line of cell division, whereas the phragmoplast, another plant-specific array, executes cell division by maintaining this predicted line. Although establishment of these specific arrays apparently involves intracellular repolarization events that focus cellular resources to a division site, it still remains unclear how microtubules position the cell division planes. Here we study GFP-AtEB1 decorated microtubule plus-ends to dissect events at the division plane. RESULTS: Early mitotic events included guided growth of endoplasmic microtubules (EMTs) towards the PPB site and their coincident localization with endocytic vesicles. Consequently, an endosomal belt lay in close proximity to the microtubular PPB at its maturation and was maintained during spindle formation. During cytokinesis, EMTs radiated from the former spindle poles in a geometrical conformation correlating with cell-plate navigation and tilt-correction. Naphthylphtalamic acid (NPA), an inhibitor of polar auxin efflux, caused abnormal PPBs and shifted division planes. CONCLUSION: Our observations reveal a spatio-temporal link between microtubules and intracellular polarization essential for localized endocytosis and precise establishment of the division plane in plants. Additionally, they implicate the growth regulator, auxin, in this important cellular event

Development of multifunction ladder

The objective of this thesis is to develop and fabricate the multifunction ladder and to minimize the manufacturing cost. Ladder is equipment that can easier consumer’s daily activities at higher place. It is stable and safe to use. The concept of this project is based on student’s creativity. The characteristics of material to fabricate this ladder are lightweight, longer life span, corrosion resistance and can take maximum load. Thus, the suitable material that accomplished those characteristics is aluminium alloy. In this thesis, we’ll also be having more to the fabrication of this ladder

Constitutive Expressor of Pathogenesis-Related Genes5 affects cell wall biogenesis and trichome development

<p>Abstract</p> <p>Background</p> <p>The Arabidopsis thaliana <it>CONSTITUTIVE EXPRESSOR OF PATHOGENESIS-RELATED GENES5 </it>(<it>CPR5</it>) gene has been previously implicated in disease resistance, cell proliferation, cell death, and sugar sensing, and encodes a putative membrane protein of unknown biochemical function. Trichome development is also affected in <it>cpr5 </it>plants, which have leaf trichomes that are reduced in size and branch number.</p> <p>Results</p> <p>In the work presented here, the role of <it>CPR5 </it>in trichome development was examined. Trichomes on <it>cpr5 </it>mutants had reduced birefringence, suggesting a difference in cell wall structure between <it>cpr5 </it>and wild-type trichomes. Consistent with this, leaf cell walls of <it>cpr5 </it>plants contained significantly less paracrystalline cellulose and had an altered wall carbohydrate composition. We also found that the effects of <it>cpr5 </it>on trichome size and endoreplication of trichome nuclear DNA were epistatic to the effects of mutations in <it>triptychon </it>(<it>try</it>) or overexpression of <it>GLABRA3</it>, indicating that these trichome developmental regulators are dependant on <it>CPR5 </it>function for their effects on trichome expansion and endoreplication.</p> <p>Conclusion</p> <p>Our results suggest that <it>CPR5 </it>is unlikely to be a specific regulator of pathogen response pathways or senescence, but rather functions either in cell wall biogenesis or in multiple cell signaling or transcription response pathways.</p

TheSTUDGene Is Required for Male-Specific Cytokinesis after Telophase II of Meiosis inArabidopsis thaliana

AbstractDuring male meiosis in wild-typeArabidopsisthe pollen mother cell (PMC) undergoes two meiotic nuclear divisions in the absence of cell division. Only after telophase II is a wall formed which partitions the PMC into four microspores. Each microspore undergoes two subsequent mitotic divisions to produce one vegetative cell and two sperm cells in the mature pollen grain. In this paper we describe the isolation and the phenotypic characterization of mutations in theSTUD(STD) gene, which is specifically required for male-specific cytokinesis after telophase II of meiosis. Although the male meiotic nuclear divisions are normal instdmutant plants, no walls are formed resulting in a tetranucleate microspore. Despite the absence of cell division in the PMC, postmeiotic development in the coenocytic microspore proceeds relatively normally, resulting in the formation of large pollen grains which contain four vegetative nuclei and up to eight sperm cells. Interestingly, these enlarged pollen grains which contain multiple vegetative nuclei and extra sperm cells behave as single male gametophytes, producing only single pollen tubes and resulting in partial male fertility instdmutant plants. Characterization of the process of pollen development and pollen function instdmutants thus reveals two different types of developmental regulation. Each of the four nuclei found in astdmicrospore following meiosis is capable of independently undergoing the complete mitotic cell division (including cytokinesis) which the single nucleus of a wild-type microspore would normally undertake. The ability of the four meiotic products to independently continue through mitosis does not depend on their division into separate cells, but is controlled by some subcellular component found within the coenocytic micropsore. By contrast, the maturestdpollen grain functions as a unit and produces only a single pollen tube despite the presence of multiple nuclei within the vegetative cell, suggesting that this process is controlled at the cellular level independently of the extra subcellular components

BRANCHLESS TRICHOMES links cell shape and cell cycle control in Arabidopsis trichomes

Endoreplication, also called endoreduplication, is a modified cell cycle in which DNA is repeatedly replicated without subsequent cell division. Endoreplication is often associated with increased cell size and specialized cell shapes, but the mechanism coordinating DNA content with shape and size remains obscure. Here we identify the product of the BRANCHLESS TRICHOMES (BLT) gene, a protein of hitherto unknown function that has been conserved throughout angiosperm evolution, as a link in coordinating cell shape and nuclear DNA content in endoreplicated Arabidopsis trichomes. Loss-of-function mutations in BLT were found to enhance the multicellular trichome phenotype of mutants in the SIAMESE (SIM) gene, which encodes a repressor of endoreplication. Epistasis and overexpression experiments revealed that BLT encodes a key regulator of trichome branching. Additional experiments showed that BLT interacts both genetically and physically with STICHEL, another key regulator of trichome branching. Although blt mutants have normal trichome DNA content, overexpression of BLT results in an additional round of endoreplication, and blt mutants uncouple DNA content from morphogenesis in mutants with increased trichome branching, further emphasizing its role in linking cell shape and endoreplication. © 2011. Published by The Company of Biologists Ltd

Two-Dimensional Patterning by a Trapping/Depletion Mechanism: The Role of TTG1 and GL3 in Arabidopsis Trichome Formation

Trichome patterning in Arabidopsis serves as a model system to study how single cells are selected within a field of initially equivalent cells. Current models explain this pattern by an activator–inhibitor feedback loop. Here, we report that also a newly discovered mechanism is involved by which patterning is governed by the removal of the trichome-promoting factor TRANSPARENT TESTA GLABRA1 (TTG1) from non-trichome cells. We demonstrate by clonal analysis and misexpression studies that Arabidopsis TTG1 can act non-cell-autonomously and by microinjection experiments that TTG1 protein moves between cells. While TTG1 is expressed ubiquitously, TTG1–YFP protein accumulates in trichomes and is depleted in the surrounding cells. TTG1–YFP depletion depends on GLABRA3 (GL3), suggesting that the depletion is governed by a trapping mechanism. To study the potential of the observed trapping/depletion mechanism, we formulated a mathematical model enabling us to evaluate the relevance of each parameter and to identify parameters explaining the paradoxical genetic finding that strong ttg1 alleles are glabrous, while weak alleles exhibit trichome clusters