Adjacent Epidermal Cells Research Articles

Tissue and cellular localization of condensed tannins in poplar roots and potential association with nitrogen uptake.

Condensed tannins are common in vegetative tissues of woody plants, including in roots. In hybrid poplar (Populus tremula x alba; also known as P. x canescens) CT assays indicated they were most concentrated in younger white roots and at the root tip. Furthermore, CT-specific staining of embedded tissue sections demonstrated accumulation in root cap cells and adjacent epidermal cells, as well as a more sporadic presence in cortex cells. In older, brown roots as well as roots with secondary growth (cork zone), CT concentration was significantly lower. The insoluble fraction of CTs was greatest in the cork zone. To determine if CT accumulation correlates with nutrient uptake in poplar roots, a microelectrode ion flux measurement (MIFE™) system was used to measure flux along the root axis. Greatest NH4 + uptake was measured near the root tip, but NO3- and Ca2+ did not vary along the root length. In agreement with earlier work, providing poplars with ample nitrogen led to higher accumulation of CTs across root zones. To test the functional importance of CTs in roots directly, CT-modified transgenic plants could be important tools.

Stomatal variations and their position relative to leaf epidermal cells in ten Maple species

Abstract In the present study, we investigated the structure of stomata in seven native species of Hyrcanian forests (Acer hyrcanum, A. velutinum Boiss., A. campestre, A. platanoides L., A. cappadocicum, A. monspessulanum, A. amazandaranicum), as well as non-native species that have fully adapted (A. negundo, A. negundo variegatum, and A. palmatum). We used light and electron microscopy to determine the form and position of the stomata in relation to the leaf epidermal cells. The length, width, shape, area, perimeter, and stomatal density were all measured. Our findings revealed that the stomata type of A. negundo varengiayum, A. campestre, A. hyrcanum, A. mazandaranicum and A. monsspesulanum is anomocytic, A. platanoides and A. cappadocicum have anomocytic stomata with wavy subsidiary cells, while A. palmatum has anisocytic stomata and A. velutinum has parasitic stomata. A. negundo has actinocytic stomata. Regarding the location of stomata relative to adjacent epidermal cells, we identified three types. In the first type, the stomata were flush with adjacent epidermal cells (A. cappadocicum, A. negundo, A. platanoides). In the second type, the stomata were higher (A. negundo variegatum), and in the third type, the stomata were lower (A. velutinum, A. monspesulanom, A. campestre, A. mazandaranicum, A. hyrcanum). The principal component analysis was used to determine the essential stomatal traits in differentiating between species. We also investigated the distribution of trees in the coordinate axis space based on two main components and performed cluster analysis based on stomatal characteristics. A. platanoides, A. negundo, A. negundo variegatum were in one cluster, while the other species were in separate clusters. The calculation of dissimilarity among the studied species revealed the lowest similarity between A. negundo and A. hyrcanum and the highest similarity between A. campestre and A. mazandaranicum. The results of the discriminant analysis identified stomatal density as the essential factor in differentiation between the studied species.

Leaf physiology and histopathology of the interaction between the opportunistic phytopathogen Fusarium equiseti and Gossypium hirsutum plants

Fungal diseases constitute a major challenge in the cultivation of the world's most important textile plant, cotton. Opportunistic fungi attack plants and promote physiological alterations and tissue damage, thereby causing losses in productivity. Herein, the hypothesis that Gossypium hirsutum L. plants are physiologically affected, depending on the phenological stage and site of infection (root system or leaf), when affected by the opportunistic phytopathogen Fusarium equiseti was tested. To this end, the photosynthetic pigment production, gas exchange, chlorophyll a fluorescence, and histopathological mechanisms involved in the plant-phytopathogen interaction were evaluated. This study aimed to diagnose the most aggressive route of infection by comparing infection via root with infection via the leaf, and to identify the developmental stage with the highest susceptibility by comparing different phenological stages. Cotton plants show metabolic losses at the maturation stage, resulting in low photosynthetic pigment concentrations, low photosynthetic rates, and photochemical stress. However, when infected by F. equiseti in the root region, the photosynthesis and photochemistry of these plants are more affected than plants inoculated in the leaf region. Low net photosynthesis (A) and water use efficiency (WUE) rates, but high light absorption flux (ABS/RC) and energy dissipation flux (DI0/RC) values were observed. Regardless of the phenological stage, the presence of F. equiseti in the roots of cotton plants caused high transpiratory rates in the plants, suggesting non-stomatic water loss and photochemical damage. In contrast, non-inoculated plants produced more photosynthetic pigments and showed higher WUE and photochemical efficiency, as indicated by the high PIABS values. Leaf histopathology assessment revealed more fragile regions of the epidermis, such as the contact region between the guard cells and adjacent epidermal cells, as well as the basal region of glandular trichomes as important access routes for F. equiseti to the inner leaf layers at all developmental stages. This study confirmed that the root colonization of cotton plants with F. equiseti can more intensely impact the physiological quality of the plants, regardless of the developmental stage.

Detection and quantification of cotton trichomes by deep learning algorithm

Cotton is one of the most economically important agricultural crops with the harvest of cotton fibers. Trichomes are initiated from the plant epidermis, which is responsible for plant resistance to many abiotic and biotic stresses. Cotton fibers share similar underlying developmental molecular mechanisms with trichomes on the stem and leaf margins of cotton. Compared with fibers, it is easier to observe the trichome phenotype of cotton stem and leaf margins. However, because of the variability in coloration and the high occlusion of the trichomes, counting the density and observing the distribution of trichomes is still highly laborious. To help resolve this problem, the present research provides a solution based on deep learning in the screening of cotton trichomes, which makes it possible to monitor the phenotype of the cotton efficiently. With a fluorescent microscopy imaging procedure, we clearly observed that there are two types of trichome phenotype inGossypium hirsutum(‘TM-1′), which are singled and clustered trichomes. The clustered trichome originates from two or more adjacent epidermal cells with no branches. The TM1 trichome was used to create a collection of singled and clustered trichome pictures. Following data production, we evaluated the effectiveness of several you only look once (YOLO) model iterations in the context of identifying singled and clustered trichomes, respectively. Results show that the YOLOv5s model outperforms YOLOv3 and YOLOv4 in average accuracy, recall, accuracy, and F1 score. We utilized the clustered trichome data set to assess the performance of YOLOv5s and Mask R-CNN in order to more precisely detect the real trichome distribution with simultaneous detection of single and clustered trichomes. The obtained findings show that both models may be utilized to concurrently identify singled and clustered trichomes since the discrepancy between the detected values of the two models and the real values is quite minimal. Mask R-CNN has a high IOU value, whereas YOLOv5s has a low false-positive detection rate and fast detection speed. Our models and datasets can be used as a starting point to measure the trichome trait in other cotton species and establish a cotton trichome detection and counting system based on deep learning technology.

Intercellular Communication during Stomatal Development with a Focus on the Role of Symplastic Connection.

Stomata are microscopic pores on the plant epidermis that serve as a major passage for the gas and water exchange between a plant and the atmosphere. The formation of stomata requires a series of cell division and cell-fate transitions and some key regulators including transcription factors and peptides. Monocots have different stomatal patterning and a specific subsidiary cell formation process compared with dicots. Cell-to-cell symplastic trafficking mediated by plasmodesmata (PD) allows molecules including proteins, RNAs and hormones to function in neighboring cells by moving through the channels. During stomatal developmental process, the intercellular communication between stomata complex and adjacent epidermal cells are finely controlled at different stages. Thus, the stomata cells are isolated or connected with others to facilitate their formation or movement. In the review, we summarize the main regulation mechanism underlying stomata development in both dicots and monocots and especially the specific regulation of subsidiary cell formation in monocots. We aim to highlight the important role of symplastic connection modulation during stomata development, including the status of PD presence at different cell-cell interfaces and the function of relevant mobile factors in both dicots and monocots.

Mechanical force drives the initial mesenchymal-epithelial interaction during skin organoid development.

Rationale: Stem cells self-organize to form organoids that generate mini-organs that resemble the physiologically-developed ones. The mechanism by which the stem cells acquire the initial potential for generating mini-organs remains elusive. Here we used skin organoids as an example to study how mechanical force drives initial epidermal-dermal interaction which potentiates skin organoids to regenerate hair follicles. Methods: Live imaging analysis, single-cell RNA-sequencing analysis, and immunofluorescence were used to analyze the contractile force of dermal cells in skin organoids. Bulk RNA-sequencing analysis, calcium probe detection, and functional perturbations were used to verify that calcium signaling pathways respond to the contractile force of dermal cells. In vitro mechanical loading experiment was used to prove that the stretching force triggers the epidermal Piezo1 expression which negatively regulates dermal cell attachment. Transplantation assay was used to test the regenerative ability of skin organoids. Results: We found that dermal cell-derived contraction force drives the movement of dermal cells surrounding the epidermal aggregates to trigger initial mesenchymal-epithelial interaction (MEI). In response to dermal cell contraction force, the arrangement of the dermal cytoskeleton was negatively regulated by the calcium signaling pathway which further influences dermal-epidermal attachment. The native contraction force generated from the dermal cell movement exerts a stretching force on the adjacent epidermal cells, activating the stretching force sensor Piezo1 in the epidermal basal cells during organoid culture. Epidermal Piezo1 in turn drives strong MEI to negatively regulate dermal cell attachment. Proper initial MEI by mechanical-chemical coupling during organoid culture is required for hair regeneration upon transplantation of the skin organoids into the back of the nude mice. Conclusion: Our study demonstrated that mechanical-chemical cascade drives the initial event of MEI during skin organoid development, which is fundamental to the organoid, developmental, and regenerative biology fields.

250 Effect of organic osmolytes improving skin’s barrier function

Tight junctions connect adjacent epidermal cells contributing to maintenance of the skin protective permeability barrier, and disturbances in this barrier may result various diseases. We investigated the effect of osmolyte candidates, betaine, proline, serine and inositol, as combination (GENENCARE® OSMS PRO) and as single compounds, and their contribution to skin barrier function by two exemplary methods: analyzing the diffusion of topically applied caffeine through reconstructed human epidermis (RHE) and by measuring transepithelial electric resistance (TEER) of differentiated normal human epidermal keratinocytes (NHEKs). RHE were treated with the osmolytes systemically, and the diffusion of radioactive 14C¬caffeine through the RHE was followed. NHEK cells were cultured on inserts and after three days of differentiation in high calcium concentration, the test substances were applied apically to the cells, and the effect on tight junction integrity was measured using chopstick electrodes. The systemic osmolyte combinations of betaine, L-proline, L-serine and myo-inositol (3 and 10 mg/ml), induced a decrease of caffeine diffusion through the RHE, during the first two hours with a significant effect at 30 min and 1 h compared to medium control, indicating stronger epidermal structure and barrier function in the osmolyte treated RHE. Betaine alone (3 mg/ml) induced a decrease of caffeine diffusion only after 30 min while L-proline alone (3 and 10 mg/ml) did not decrease caffeine diffusion. Application of topical osmolyte combination (10 mg/ml) resulted increase in %change in TEER values of 28% (at 2 h), 28% (at 3 h) and 43% (at 5 h) compared to medium control without osmolytes having %change in TEER -5 %, -7 % and 14 %, respectively. 0.15 M NaCl, which modelled the hyperosmotic stress, resulted significant decrease in %change in TEER in all time points. The results indicate that osmolytes may have beneficial effects on epidermal permeability barrier and tight junction integrity, that might be especially advantageous during a stress compromising the function of the tight junctions and permeability barrier.

A Face-Split Study to Evaluate the Effects of Microneedle Radiofrequency with Q-Switched Nd:YAG Laser for the Treatment of Melasma.

BackgroundLaser toning using a low-fluence 1,064 nm Q-switched Nd:YAG laser is one of the most frequently used treatment modalities for melasma. However, this therapy is time consuming because it requires a lot of treatment sessions. Recently, it has been reported that transdermal radiofrequency (RF) is effective for the treatment of melasma.ObjectiveTo determine whether microneedle RF conduction could be an adjunct therapy for melasma, we have studied the effect of simultaneous treatments with laser toning and RF for melasma.MethodsFifteen patients with melasma underwent five sessions of laser toning and microneedle RF on the right side of the face, and only laser toning on the left side. Responses to treatments were evaluated using the Mexameter® (Courage Khazaka, Germany) score, the pigmentation and severity index (PSI) score, and the patient's overall assessment. Additionally, an electron microscopic study of a skin biopsy was performed.ResultsBoth laser toning and combination therapy showed significant decreases in the Mexameter® and PSI score after five treatment sessions. Combination therapy showed a more significant improvement of melasma than laser toning. No remarkable side effects were reported. Electron microscopic analysis showed a greater number of vacuolar changes and increased loosening of melanocytes and adjacent epidermal cells after combination therapy.ConclusionThe combination treatment of laser toning and microneedle RF therapy showed a better therapeutic effect for melasma than laser toning alone. Therefore, the microneedle RF technique could be a new and safe adjunct therapy for the treatment of melasma.

Contrasting pectin polymers in guard cell walls of Arabidopsis and the hornwort Phaeoceros reflect physiological differences

In seed plants, stomata regulate CO2 acquisition and water relations via transpiration, while minimizing water loss. Walls of guard cells are strong yet flexible because they open and close the pore by changing shape over the substomatal cavity. Pectins are necessary for wall flexibility and proper stomata functioning. This study investigates the differences in pectin composition in guard cells of two taxa that represent key lineages of plants with stomata: Arabidopsis, an angiosperm with diurnal stomatal activity, and Phaeoceros, a bryophyte that lacks active stomatal movement. Using immunolocalization techniques in transmission electron microscopy, this study describes and compares the localization of pectin molecule epitopes essential to stomata function in guard cell walls of Arabidopsis and Phaeoceros. In Arabidopsis, unesterified homogalacturonans very strongly localize throughout guard cell walls and are interspersed with arabinan pectins, while methyl-esterified homogalacturonans are restricted to the exterior of the wall, the ledges and the junction with adjacent epidermal cells. In contrast, arabinans are absent in Phaeoceros, and both unesterified and methyl-esterified homogalacturonans localize throughout guard cell walls. Arabinans and unesterified homogalacturonans are required for wall flexibility, which is consistent with active regulation of pore opening in Arabidopsis stomata. In contrast, the lack of arabinans and high levels of methyl-esterified homogalacturonans in guard cell walls of Phaeoceros are congruent with the inability of hornwort stomata to open and close with environmental change. Comparisons across groups demonstrate that variations in guard cell wall composition reflect different physiological activity of stomata in land plants.

Adding a Piece to the Leaf Epidermal Cell Shape Puzzle

The jigsaw puzzle-shaped pavement cells in the leaf epidermis collectively function as a load-bearing tissue that controls organ growth. In this issue of Developmental Cell, Majda etal. (2017) shed light on how the jigsaw shape can arise from localized variations in wall stiffness between adjacent epidermal cells.

Emergent cellular self-organization and mechanosensation initiate follicle pattern in the avian skin.

The spacing of hair in mammals and feathers in birds is one of the most apparent morphological features of the skin. This pattern arises when uniform fields of progenitor cells diversify their molecular fate while adopting higher-order structure. Using the nascent skin of the developing chicken embryo as a model system, we find that morphological and molecular symmetries are simultaneously broken by an emergent process of cellular self-organization. The key initiators of heterogeneity are dermal progenitors, which spontaneously aggregate through contractility-driven cellular pulling. Concurrently, this dermal cell aggregation triggers the mechanosensitive activation of β-catenin in adjacent epidermal cells, initiating the follicle gene expression program. Taken together, this mechanism provides a means of integrating mechanical and molecular perspectives of organ formation.

مطالعه صفات تشریحی برگ و دمبرگ سرده Alchemilla از تیره گل سرخیان در ایران و کاربرد آنها در تاکسونومی عددی

The current study deals with leaf and petiole anatomical survey of 24 species of the genus Alchemilla from Iran. After collecting and identifying the specimens, leaf and petiole cross sections were prepared by hand and best sections were taken for staining and light microscope studies. In this survey, 43 anatomical traits were carefully examined. The result showed that glandular trichome, number and arrangement of adjacent epidermal cells and their wavy or smooth walls, presence and absence of the extraxylary fibers are the most outstanding anatomical evidences. In order to determine the species relationship, 39 quantitative characters were undertaken in principal component analysis (PCA). PCA analysis led to complete separation of some species including A. persica, A. caucasica, A. hessii, A. pseudocartalinica, A. rechingeri, A. melancholica, A. hyrcana, A. microscopica and A. erythropoda, formation of 3 main groups and two subgroups. Our findings revealed that leaf and petiole anatomical characters are limited taxonomic value. The numerical analysis of these traits has disability in revealing the species relationship.

Maize leaf trichomes represent an entry point of infection for Fusarium species

Fifteen day old maize seedlings were inoculated with Fusarium graminearum, Fusarium proliferatum, and Fusarium verticillioides. More than 90 % F. proliferatum and F. verticillioides conidia and 50 % of F. graminearum formed one germ tube whereas the other 50 % of F. graminearum conidia formed two to three germ tubes. The germ tubes of F. graminearum conidia were longer than those of F. proliferatum and F. verticillioides. The three species of Fusarium infected bi-cellular trichomes by adhering and growing along the trichomes or by attaching to the cap cell of the trichomes 48 h after inoculation. Hyphae penetrated into the trichomes at the base, the side or at the top of the cap cells. The hyphae colonized the cap cells and then spread to base cells. Prickle trichomes were infected 72 h after inoculation. The hyphae either wrapped around prickle trichomes or formed a mass of hyphae around the top of prickle trichomes or formed appressorium. Macro trichomes were infected by F. graminearum 7 d after inoculation. Following penetration, the fungus spread to adjacent epidermal cells and to the subcuticle. This investigation provides the first assessment of F. graminearum, F. proliferatum, and F. verticillioides infection via trichomes of maize leaves.

Isolation and Phenotypic Characterization of Lotus japonicus Mutants Specifically Defective in Arbuscular Mycorrhizal Formation

Several symbiotic mutants of legume plants defective in nodulation have also been shown to be mutants related to arbuscular mycorrhizal (AM) symbiosis. The origin of the AM symbiosis can be traced back to the early land plants. It has therefore been postulated that the older system of AM symbiosis was partially incorporated into the newer system of legume-rhizobium symbiosis. To unravel the genetic basis of the establishment of AM symbiosis, we screened about 34,000 plants derived from ethyl methanesulfonate (EMS)-mutagenized Lotus japonicus seeds by microscopic observation. As a result, three lines (ME778, ME966 and ME2329) were isolated as AM-specific mutants that exhibit clear AM-defective phenotypes but form normal effective root nodules with rhizobial infection. In the ME2329 mutant, AM fungi spread their hyphae into the intercellular space of the cortex and formed trunk hyphae in the cortical cells, but the development of fine branches in the arbuscules was arrested. The ME2329 mutant carried a nonsense mutation in the STR-homolog gene, implying that the line may be an str mutant in L. japonicus. On the ME778 and ME966 mutant roots, the entry of AM fungal hyphae was blocked between two adjacent epidermal cells. Occasionally, hyphal colonization accompanied by arbuscules was observed in the two mutants. The genes responsible for the ME778 and ME966 mutants were independently located on chromosome 2. These results suggest that the ME778 and ME966 lines are symbiotic mutants involved in the early stage of AM formation in L. japonicus.

Stomatal encryption by epicuticular waxes as a plastic trait modifying gas exchange in a Mediterranean evergreen species (Quercus coccifera L.)

The adaptive benefit of stomatal crypts remains a matter of controversy. This work studies the effect on gas exchange of cuticular rims that overarch the stomatal pore in the Mediterranean species Quercus coccifera L. growing under Mediterranean (lower relative humidities and high summer temperatures) or oceanic conditions (higher daily relative humidities and mild temperatures). After microscopic assessment of the leaf surfaces and stomatal architecture, the impact of the cuticular 'cup' on gas exchange was evaluated by employing three-dimensional finite element models. Here, we provide evidence for a high plasticity of the Q. coccifera cuticular cup, with much larger vents under oceanic conditions compared to small vents under Mediterranean conditions. This structure adds a substantial fixed resistance thereby strongly decreasing gas exchange under Mediterranean conditions. The cuticular cup, which also increases leaf internal humidity, might buffer the rapid changes in vapour pressure deficit (VPD) often observed under Mediterranean conditions. Since water loss of guard and adjacent epidermal cells regulates stomatal aperture, we suggest that this structure allows an efficient regulation of stomatal conductance and optimum use of resources under high VPD. This study provides evidence that plasticity of stomatal architecture can be an important structural component of hydraulic adaptation to different climate conditions.

Infection and establishment of Ascochyta anemones in leaves of windflower

Leaf spot, caused by Ascochyta anemones, is one of the major diseases of windflower in China. Histological studies of the artificially inoculated leaf tissues with A. anemonesconidia were observed by light and electron microscopy to elucidate the host-pathogen interaction. Conidial germination and germ tube formation began after 4 h of inoculation. Each conidium produced one germ tube which penetrated the host surface. The fungus gain entry of the host by direct penetration of the leaf cuticle, following the formation of appressorium after 12-24 h of inoculation. Most appressoria were formed in the grooves between adjacent epidermal cells. Once the fungus was fully established, it destroyed internal tissues, resulting in diseased lesions on the leaves after 3-6 days of inoculation. Development of leaf spots and fungal pycnidia could be observed on necrotic areas within 7-14 days after inoculation. Key words: Windflower, Ascochyta anemones, infection process.

An Avirulent Tomato Powdery Mildew Isolate Induces Localized Acquired Resistance to a Virulent Isolate in a Spatiotemporal Manner

Hypersensitive response (HR) of plant cells to the attack of pathogens induces resistance to subsequent attacks by a broad spectrum of pathogens, leading to acquired resistance. In this study, we characterized the localized acquired resistance (LAR) in the epidermal cells of tomato. First, we report the discovery of a new isolate of tomato powdery mildew occurring in Japan, KTP-02, which has a different virulence spectrum compared with the previously-characterized isolate, KTP-01. Using these two isolates, we investigated LAR phenomenon in the epidermal cells of tomato plants carrying the Ol-4 resistance gene. Ol-4 encodes a nucleotide-binding site leucine-rich repeat protein that triggers HR in the epidermal cells in response to KTP-01 but not KTP-02. We mounted a single conidium of KTP-01 on a single tomato epidermal cell and then monitored the progress of HR in that cell by live microscopy. Once HR occurred in that cell, we mounted a single conidium of KTP-02 on cells adjacent to or at one-cell distance from the first challenged cells, in different time points. With a digital microscope, we consecutively tracked the progress of HR (i.e., induction of LAR) in those cells. Results showed that, in tomato plants carrying the Ol-4 gene, HR to KTP-01 results in induction of HR in the adjacent epidermal cells challenged with KTP-02. Our results show that LAR can be triggered only in adjacent cell layer and lasts 24 to 48 h after HR occurred in the first cell. We did not observe the reverse phenomenon, induced susceptibility to KTP-01 by KTP-02. Altogether, we report an advanced technique for investigating LAR phenomena, and provide data on spatiotemporal characteristics of LAR in tomato epidermal cells.

Nitric oxide modulates ozone‐induced cell death, hormone biosynthesis and gene expression in Arabidopsis thaliana

Nitric oxide (NO) is involved together with reactive oxygen species (ROS) in the activation of various stress responses in plants. We have used ozone (O₃) as a tool to elicit ROS-activated stress responses, and to activate cell death in plant leaves. Here, we have investigated the roles and interactions of ROS and NO in the induction and regulation of O₃-induced cell death. Treatment with O₃ induced a rapid accumulation of NO, which started from guard cells, spread to adjacent epidermal cells and eventually moved to mesophyll cells. During the later time points, NO production coincided with the formation of hypersensitive response (HR)-like lesions. The NO donor sodium nitroprusside (SNP) and O₃ individually induced a large set of defence-related genes; however, in a combined treatment SNP attenuated the O₃ induction of salicylic acid (SA) biosynthesis and other defence-related genes. Consistent with this, SNP treatment also decreased O₃-induced SA accumulation. The O₃-sensitive mutant rcd1 was found to be an NO overproducer; in contrast, Atnoa1/rif1 (Arabidopsis nitric oxide associated 1/resistant to inhibition by FSM1), a mutant with decreased production of NO, was also O₃ sensitive. This, together with experiments combining O₃ and the NO donor SNP suggested that NO can modify signalling, hormone biosynthesis and gene expression in plants during O₃ exposure, and that a functional NO production is needed for a proper O₃ response. In summary, NO is an important signalling molecule in the response to O₃.

The TTG1-bHLH-MYB complex controls trichome cell fate and patterning through direct targeting of regulatory loci

A network of three classes of proteins consisting of bHLH and MYB transcription factors, and a WD40 repeat protein, TRANSPARENT TESTA GLABRA1 (TTG1), act in concert to activate trichome initiation and patterning. Using YFP-TTG1 translational fusions, we show that TTG1 is expressed ubiquitously in Arabidopsis leaves and is preferentially localized in the nuclei of trichomes at all developmental stages. Using a conditional transgenic allele, we demonstrate that TTG1 directly targets the same genes as the bHLH protein GLABRA3 (GL3). In vivo binding of the R2R3-MYB protein GLABRA1 (GL1) to the promoters of GLABRA2 (GL2), TRANSPARENT TESTA GLABRA2 (TTG2), CAPRICE (CPC) and ENHANCER OF TRIPTYCHON AND CAPRICE1 (ETC1) establishes that these genes are major transcriptional targets for the TTG1-bHLH-MYB regulatory complex. By co-precipitation, we confirm that TTG1 associates with GL3 and GL1 in vivo, forming a complex. The loss of TTG1 and GL1 through mutation, affects the subcellular distribution of GL3. Using particle bombardment, we show that TTG1, GL3, GL1 and the homeodomain protein GL2 do not move between adjacent epidermal cells, while the R3-MYB, CPC, does move to neighboring cells. These data support a model for the TTG1 complex directly regulating activators and repressors and the movement of repressors to affect trichome patterning on the Arabidopsis leaf.

Muscle cell migrations of C. elegans are mediated by the α-integrin INA-1, Eph receptor VAB-1, and a novel peptidase homologue MNP-1

Cell migration is a fundamental process occurring during embryonic development and tissue morphogenesis. In the nematode Caenorhabditis elegans, morphogenesis of the body-wall musculature involves short-range migrations of 81 embryonic muscle cells from the lateral surface of the embryo towards the dorsal and ventral midlines. This study shows that mutations in ina-1 (α-integrin), as well as vab-1 (Eph receptor), and vab-2 (ephrin), display defects in embryonic muscle cell migration. Furthermore, an RNAi-based enhancer screen in an ina-1 weak loss-of-function background identified mnp-1 (matrix non-peptidase homologue-1) as a previously uncharacterized gene required for promoting proper migration of the embryonic muscle cells. mnp-1 encodes a membrane associated metalloproteinase homologue that is predicted to be catalytically inactive. Our data suggest that MNP-1 is expressed in migrating muscle cells and localizes to the plasma membrane with the non-peptidase domain exposed to the extra-cellular environment. Double-mutant analysis between mnp-1(RNAi), ina-1, and vab-1 mutations; as well as tissue specific rescue experiments; indicated that each of these gene products function predominantly independent of each other and from different cell types to affect muscle cell migration. Together these results suggest complex interactions between the adjacent epidermal, neuronal, and muscle cells are required to promote proper muscle cell migration during embryogenesis.