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Stomatal pores in leaves mediate CO2 uptake into the plant and water loss via transpiration. Most plants are hypostomatous with stomata present only in the lower leaf surface (abaxial epidermis). Many herbs, including the model plant Arabidopsis, have substantial numbers of stomata also on the upper (adaxial) leaf surface. Studies of stomatal development have mostly focused on abaxial stomata and very little is known of adaxial stomatal formation. We analysed the role of leaf number in determining stomatal density and stomatal ratio, and studied adaxial and abaxial stomatal patterns in Arabidopsis mutants deficient in known abaxial stomatal development regulators. We found that stomatal density in some genetic backgrounds varies between different fully expanded leaves, and thus we recommend using defined leaves for analyses of stomatal patterning. Our results indicate that stomatal development is at least partly independently regulated in adaxial and abaxial epidermis, as (i) plants deficient in ABA biosynthesis and perception have increased stomatal ratios, (ii) the epf1epf2, tmm, and sdd1 mutants have reduced stomatal ratios, (iii) erl2 mutants have increased adaxial but not abaxial stomatal index, and (iv) stomatal precursors preferentially occur in abaxial epidermis. Further studies of adaxial stomata can reveal new insights into stomatal form and function., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Plant prickles are controlled by genes involved in the final step of cytokinin biosynthesis.

Plant leaves consist of three layers, including epidermis, mesophyll and vascular tissues. Their development is meticulously orchestrated. Stomata are the specified structures on the epidermis for uptake of carbon dioxide (CO 2 ) while release of water vapour and oxygen (O 2 ), and thus play essential roles in regulation of plant photosynthesis and water use efficiency. To function efficiently, stomatal formation must coordinate with the development of other epidermal cell types, such as pavement cell and trichome, and tissues of other layers, such as mesophyll and leaf vein. This review summarizes the regulation of stomatal development in three dimensions (3D). In the epidermis, specific stomatal transcription factors determine cell fate transitions and also activate a ligand-receptor- MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) signaling for ensuring proper stomatal density and patterning. This forms the core regulation network of stomatal development, which integrates various environmental cues and phytohormone signals to modulate stomatal production. Under the epidermis, mesophyll, endodermis of hypocotyl and inflorescence stem, and veins in grasses secrete mobile signals to influence stomatal formation in the epidermis. In addition, long-distance signals which may include phytohormones, RNAs, peptides and proteins originated from other plant organs modulate stomatal development, enabling plants to systematically adapt to the ever changing environment., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

The placenta in fruits of most plants either desiccate and shrink as the fruits mature or develop further to form the fleshy tissues. In poplars, placental epidermal cells protrude collectively to produce catkin fibers. In this study, three carpel limited MIXTA genes, PdeMIXTA02, PdeMIXTA03, PdeMIXTA04, were find to specifically expressed in carpel immediately after pollination. Heterologous expression of the three genes in Arabidopsis demonstrated that PdeMIXTA04 significantly promoted trichomes density and could restore trichomes in the trichomeless mutant. By contrast, such functions were not observed with PdeMIXTA02, PdeMIXTA03. In situ hybridization revealed that PdeMIXTA04 was explicitly expressed in poplar placental epidermal cells. We also confirmed trichome-specific expression of the PdeMIXTA04 promoter. Multiple experimental proofs have confirmed the interaction between PdeMIXTA04, PdeMYC and PdeWD40, indicating PdeMIXTA04 functioned through the MYB-bHLH-WD40 ternary complex. Our work provided distinctive understanding of the molecular mechanism triggering differentiation of poplar catkins., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

The alternating cell specifications of root epidermis to form hair cells or nonhair cells in Arabidopsis are determined by the expression level of GL2 , which is activated by an MYB-bHLH-WD40 (WER-GL3-TTG1) transcriptional complex. The phytohormone ethylene (ET) has a unique effect of inducing N-position epidermal cells to form root hairs. However, the molecular mechanisms underlying ET-induced ectopic root hair development remain enigmatic. Here, we show that ET promotes ectopic root hair formation through down-regulation of GL2 expression. ET-activated transcription factors EIN3 and its homolog EIL1 mediate this regulation. Molecular and biochemical analyses further revealed that EIN3 physically interacts with TTG1 and interferes with the interaction between TTG1 and GL3, resulting in reduced activation of GL2 by the WER-GL3-TTG1 complex. Furthermore, we found through genetic analysis that the master regulator of root hair elongation, RSL4, which is directly activated by EIN3, also participates in ET-induced ectopic root hair development. RSL4 negatively regulates the expression of GL2 , likely through a mechanism similar to that of EIN3. Therefore, our work reveals that EIN3 may inhibit gene expression by affecting the formation of transcription-activating protein complexes and suggests an unexpected mutual inhibition between the hair elongation factor, RSL4, and the hair specification factor, GL2. Overall, this study provides a molecular framework for the integration of ET signaling and intrinsic root hair development pathway in modulating root epidermal cell specification., Competing Interests: The authors declare no competing interest.

Shoot regeneration involves reprogramming of somatic cells and de novo organization of shoot apical meristems (SAMs). In the best-studied model system of shoot regeneration using Arabidopsis, regeneration is mediated by the auxin-responsive pluripotent callus formation from pericycle or pericycle-like tissues according to the lateral root development pathway. In contrast, shoot regeneration can be induced directly from fully differentiated epidermal cells of stem explants of Torenia fournieri (Torenia), without intervening the callus mass formation in culture with cytokinin; yet, its molecular mechanisms remain unaddressed. Here, we characterized this direct shoot regeneration by cytological observation and transcriptome analyses. The results showed that the gene expression profile rapidly changes upon culture to acquire a mixed signature of multiple organs/tissues, possibly associated with epidermal reprogramming. Comparison of transcriptomes between three different callus-inducing cultures (callus induction by auxin, callus induction by wounding and protoplast culture) of Arabidopsis and the Torenia stem culture identified genes upregulated in all the four culture systems as candidates of common factors of cell reprogramming. These initial changes proceeded independently of cytokinin, followed by cytokinin-dependent, transcriptional activations of nucleolar development and cell cycle. Later, SAM regulatory genes became highly expressed, leading to SAM organization in the foci of proliferating cells in the epidermal layer. Our findings revealed three distinct phases with different transcriptomic and regulatory features during direct shoot regeneration from the epidermis in Torenia, which provides a basis for further investigation of shoot regeneration in this unique culture system., (© The Author(s) 2021. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.)

As an adaptive innovation in plant terrestrialization, cuticle covers the plant surface and greatly contributes to the development and stress tolerance in land plants. Although past decades have seen great progress in understanding the molecular mechanism of cuticle biosynthesis in flowering plants with the contribution of cuticle biosynthesis mutants and advanced cuticle composition profiling techniques, origins and evolution of cuticle biosynthesis are poorly understood. Recent chemical, phylogenomic, and molecular genetic studies on cuticle biosynthesis in early-diverging extant land plant lineages, the bryophytes, shed novel light on the origins and evolution of plant cuticle biosynthesis. In this mini-review, we highlighted these recent advances in the molecular biology of cuticle biosynthesis in bryophytes, and provided evolutionary insights into plant cuticle biosynthesis.

The shoot apical meristem allows for reiterative formation of new aerial structures throughout the life cycle of a plant. We use single-cell RNA sequencing to define the cellular taxonomy of the Arabidopsis vegetative shoot apex at the transcriptome level. We find that the shoot apex is composed of highly heterogeneous cells, which can be partitioned into 7 broad populations with 23 transcriptionally distinct cell clusters. We delineate cell-cycle continuums and developmental trajectories of epidermal cells, vascular tissue, and leaf mesophyll cells and infer transcription factors and gene expression signatures associated with cell fate decisions. Integrative analysis of shoot and root apical cell populations further reveals common and distinct features of epidermal and vascular tissues. Our results, thus, offer a valuable resource for investigating the basic principles underlying cell division and differentiation in plants at single-cell resolution., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Cutin is a polyester matrix mainly composed of hydroxy-fatty acids that occurs in the cuticles of shoots and root-caps. The cuticle, of which cutin is a major component, protects the plant from biotic and abiotic stresses, and cutin has been postulated to constrain organ expansion. We propose that, to allow cutin restructuring, ester bonds in this net-like polymer can be transiently cleaved and then re-formed (transacylation). Here, using pea epicotyl epidermis as the main model, we first detected a cutin:cutin-fatty acid endo-transacylase (CCT) activity. In-situ assays used endogenous cutin as the donor substrate for endogenous enzymes; the exogenous acceptor substrate was a radiolabelled monomeric cutin-acid, 16-hydroxy-[3H]hexadecanoic acid (HHA). High-molecular-weight cutin became ester-bonded to intact [3H]HHA molecules, which thereby became unextractable except by ester-hydrolysing alkalis. In-situ CCT activity correlated with growth rate in Hylotelephium leaves and tomato fruits, suggesting a role in loosening the outer epidermal wall during organ growth. The only well-defined cutin transacylase in the apoplast, CUS1 (a tomato cutin synthase), when produced in transgenic tobacco, lacked CCT activity. This finding provides a reference for future CCT protein identification, which can adopt our sensitive enzyme assay to screen other CUS1-related enzymes., (© 2021 The Author(s).)

Optimal plant growth is hampered by deficiency of the essential macronutrient phosphate in most soils. Plant roots can, however, increase their root hair density to efficiently forage the soil for this immobile nutrient. By generating and exploiting a high-resolution single-cell gene expression atlas of Arabidopsis roots, we show an enrichment of TARGET OF MONOPTEROS 5/LONESOME HIGHWAY (TMO5/LHW) target gene responses in root hair cells. The TMO5/LHW heterodimer triggers biosynthesis of mobile cytokinin in vascular cells and increases root hair density during low-phosphate conditions by modifying both the length and cell fate of epidermal cells. Moreover, root hair responses in phosphate-deprived conditions are TMO5- and cytokinin-dependent. Cytokinin signaling links root hair responses in the epidermis to perception of phosphate depletion in vascular cells., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The cuticle is the outermost layer of plant aerial tissue that interacts with the environment and protects plants against water loss and various biotic and abiotic stresses. ADP ribosylation factor guanine nucleotide exchange factor proteins (ARF-GEFs) are key components of the vesicle trafficking system. Our study discovers that AtMIN7, an Arabidopsis ARF-GEF, is critical for cuticle formation and related leaf surface defense against the bacterial pathogen Pseudomonas syringae pathovar tomato ( Pto ). Our transmission electron microscopy and scanning electron microscopy studies indicate that the atmin7 mutant leaves have a thinner cuticular layer, defective stomata structure, and impaired cuticle ledge of stomata compared to the leaves of wild type plants. GC-MS analysis further revealed that the amount of cutin monomers was significantly reduced in atmin7 mutant plants. Furthermore, the exogenous application of either of three plant hormones-salicylic acid, jasmonic acid, or abscisic acid-enhanced the cuticle formation in atmin7 mutant leaves and the related defense responses to the bacterial Pto infection. Thus, transport of cutin-related components by AtMIN7 may contribute to its impact on cuticle formation and related defense function.

In this report, we describe studies on symplasmic communication and cellular rearrangement during direct somatic embryogenesis (SE) in the tree fern Cyathea delgadii. We analyzed changes in the symplasmic transport of low-molecular-weight fluorochromes, such as 8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt (HPTS) and fluorescein (delivered to cells as fluorescein diacetate, FDA), within stipe explants and somatic embryos originating from single epidermal cells and developing during 16-d long culture. Induction of SE is preceded by a restriction in fluorochrome distribution between certain explant cells. Microscopic analysis showed a series of cellular changes like a decrease in vacuole size, increase in vacuole numbers, and increased density of cytoplasm and deposition of electron-dense material in cell walls that may be related with embryogenic transition. In somatic embryos, the limited symplasmic communication between cells was observed first in linear tri-cellular embryos. Further development of the fern embryo was associated with the formation of symplasmic domains corresponding to the four segments of the plant body. Using symplasmic tracers, we provided evidence that the changes in plasmodesmata permeability are corelated with somatic-to-embryogenic transition and somatic embryo development., (© The Author(s) 2020. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.)

Reproduction-specific small RNAs are vital regulators of germline development in animals and plants. MicroRNA2118 (miR2118) is conserved in plants and induces the production of phased small interfering RNAs (phasiRNAs). To reveal the biological functions of miR2118, we describe here rice mutants with large deletions of the miR2118 cluster. Our results demonstrate that the loss of miR2118 causes severe male and female sterility in rice, associated with marked morphological and developmental abnormalities in somatic anther wall cells. Small RNA profiling reveals that miR2118-dependent 21-nucleotide (nt) phasiRNAs in the anther wall are U-rich, distinct from the phasiRNAs in germ cells. Furthermore, the miR2118-dependent biogenesis of 21-nt phasiRNAs may involve the Argonaute proteins OsAGO1b/OsAGO1d, which are abundant in anther wall cell layers. Our study highlights the site-specific differences of phasiRNAs between somatic anther wall and germ cells, and demonstrates the significance of miR2118/U-phasiRNA functions in anther wall development and rice reproduction.

Main Conclusion: To compensate for the lack of capacity for external salt storage in the epidermal bladder cells, quinoa plants employ tissue-tolerance traits, to confer salinity stress tolerance. Our previous studies indicated that sequestration of toxic Na + and Cl - ions into epidermal bladder cells (EBCs) is an efficient mechanism conferring salinity tolerance in quinoa. However, some halophytes do not develop EBCs but still possess superior salinity tolerance. To elucidate the possible compensation mechanism(s) underlying superior salinity tolerance in the absence of the external salt storage capacity, we have selected four quinoa accessions with contrasting patterns of EBC development. Whole-plant physiological and electrophysiological characteristics were assessed after 2 days and 3 weeks of 400 mM NaCl stress. Both accessions with low EBC volume utilised Na + exclusion at the root level and could maintain low Na + concentration in leaves to compensate for the inability to sequester Na + load in EBC. These conclusions were further confirmed by electrophysiological experiments showing higher Na + efflux from roots of these varieties (measured by a non-invasive microelectrode MIFE technique) as compared to accessions with high EBC volume. Furthermore, accessions with low EBC volume had significantly higher K + concentration in their leaves upon long-term salinity exposures compared to plants with high EBC sequestration ability, suggesting that the ability to maintain high K + content in the leaf mesophyll was as another important compensation mechanism.

Differential growth plays a crucial role during morphogenesis [1-3]. In plants, development occurs within mechanically connected tissues, and local differences in cell expansion lead to deformations at the organ level, such as buckling or bending [4, 5]. During early seedling development, bending of hypocotyl by differential cell elongation results in apical hook structure that protects the shoot apical meristem from being damaged during emergence from the soil [6, 7]. Plant hormones participate in apical hook development, but not how they mechanistically drive differential growth [8]. Here, we present evidence of interplay between hormonal signals and cell wall in auxin-mediated differential cell elongation using apical hook development as an experimental model. Using genetic and cell biological approaches, we show that xyloglucan (a major primary cell wall component) mediates asymmetric mechanical properties of epidermal cells required for hook development. The xxt1 xxt2 mutant, deficient in xyloglucan [9], displays severe defects in differential cell elongation and hook development. Analysis of xxt1 xxt2 mutant reveals a link between cell wall and transcriptional control of auxin transporters PINFORMEDs (PINs) and AUX1 crucial for establishing the auxin response maxima required for preferential repression of elongation of the cells on the inner side of the hook. Genetic evidence identifies auxin response factor ARF2 as a negative regulator acting downstream of xyloglucan-dependent control of hook development and transcriptional control of polar auxin transport. Our results reveal a crucial feedback process between the cell wall and transcriptional control of polar auxin transport, underlying auxin-dependent control of differential cell elongation in plants., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The aerial epidermis of plants plays a major role in environmental interactions, yet the development of the cellular components of the aerial epidermis-trichomes, stomata, and pavement cells-is still not fully understood. We have performed a detailed screen of the leaf epidermis in two generations of the well-established Solanum lycopersicum cv M82 × Solanum pennellii ac. LA716 introgression line (IL) population using a combination of scanning electron microscopy (SEM) techniques. Quantification of trichome and stomatal densities in the ILs revealed four genomic regions with a consistently low trichome density. This study also found ILs with abnormal proportions of different trichome types and aberrant trichome morphologies. This work has led to the identification of new, unexplored genomic regions with roles in trichome formation in tomato. This study investigated one interval in IL2-6 in more detail and identified a new function for the transcription factor SlMixta - like in determining trichome patterning in leaves. This illustrates how these SEM images, publicly available to the research community, provide an important dataset for further studies on epidermal development in tomato and other species of the Solanaceae family., (© 2020 American Society of Plant Biologists. All rights reserved.)

The palea and lemma (hull) are grass-specific organs, and determine grain size and quality. In the study, AH2 encodes a MYB domain protein, and functions in the development of hull and grain. Mutation of AH2 produces smaller grains and alters grain quality including decreased amylose content and gel consistency, and increased protein content. Meantime, part of the hull lost the outer silicified cells, and induces a transformation of the outer rough epidermis to inner smooth epidermis cells, and the body of the palea was reduced in the ah2 mutant. We confirmed the function of AH2 by complementation, CRISPR-Cas9, and cytological and molecular tests. Additionally, AH2, as a repressor, repress transcription of the downstream genes. Our results revealed that AH2 plays an important role in the determination of hull epidermis development, palea identity, and grain size., (© 2019 The Authors The Plant Journal © 2019 John Wiley & Sons Ltd.)

The CUP-SHAPED COTYLEDON 2 ( CUC2 ) gene, which is negatively regulated by microRNA164 ( miR164 ), has been specifically linked to the regulation of leaf margin serration and the maintenance of phyllotaxy in model plants. However, few studies have investigated these effects in woody plants. In this study, we integrated genomic, transcriptomic, and physiology approaches to explore the function of BpCUC2 gene in Betula pendula growth and development. Our results showed that Betula pendula plants overexpressing BpCUC2 , which is targeted by BpmiR164 , exhibit shortened internodes and abnormal leaf shapes. Subsequent analysis indicated that the short internodes of BpCUC2 overexpressed transgenic lines and were due to decreased epidermal cell size. Moreover, transcriptome analysis, yeast one-hybrid assays, and ChIP-PCR suggested that BpCUC2 directly binds to the LTRECOREATCOR15 (CCGAC), CAREOSREP1 (CAACTC), and BIHD1OS (TGTCA) motifs of a series of IAA-related and cyclin-related genes to regulate expression. These results may be useful to our understanding of the functional role and genetic regulation of BpCUC2 .

Biodiversity in plant shape is mainly attributable to the diversity of leaf shape, which is largely determined by the transient morphogenetic activity of the leaf margin that creates leaf serrations. However, the precise mechanism underlying the establishment of this morphogenetic capacity remains poorly understood. We report here that INDOLE-3-BUTYRIC ACID RESPONSE 5 (IBR5), a dual-specificity phosphatase, is a key component of leaf-serration regulatory machinery. Loss-of-function mutants of IBR5 exhibited pronounced serrations due to increased cell area. IBR5 was localized in the nucleus of leaf epidermis and petiole cells. Introducing a C129S mutation within the highly conserved VxVHCx 2 GxSRSx 5 AYLM motif of IBR5 rendered it unable to rescue the leaf-serration defects of the ibr5-3 mutant. In addition, auxin reporters revealed that the distribution of auxin maxima was expanded ectopically in ibr5-3 . Furthermore, we found that the distribution of PIN1 on the plasma membrane of the epidermal and cells around the leaf vein was compromised in ibr5-3 . We concluded that IBR5 is essential for the establishment of PIN-FORMED 1 (PIN1)-directed auxin maxima at the tips of leaf serration, which is vital for the elaborated regulation during its formation.

Water deficit is a major environmental threat affecting crop yields worldwide. In this study, a drought stress-sensitive mutant drought sensitive 8 (ds8) was identified in rice (Oryza sativa L.). The DS8 gene was cloned using a map-based approach. Further analysis revealed that DS8 encoded a Nck-associated protein 1 (NAP1)-like protein, a component of the SCAR/WAVE complex, which played a vital role in actin filament nucleation activity. The mutant exhibited changes in leaf cuticle development. Functional analysis revealed that the mutation of DS8 increased stomatal density and impaired stomatal closure activity. The distorted actin filaments in the mutant led to a defect in abscisic acid (ABA)-mediated stomatal closure and increased ABA accumulation. All these resulted in excessive water loss in ds8 leaves. Notably, antisense transgenic lines also exhibited increased drought sensitivity, along with impaired stomatal closure and elevated ABA levels. These findings suggest that DS8 affects drought sensitivity by influencing actin filament activity., (© 2019 The Authors. The Plant Journal published by John Wiley & Sons Ltd and Society for Experimental Biology.)

Even though cell walls have essential functions for bacteria, fungi, and plants, tools to investigate their dynamic structure in living cells have been missing. Here, it is shown that changes in the intensity of the plasma membrane dye FM4-64 in response to extracellular quenchers depend on the nano-scale porosity of cell walls. The correlation of quenching efficiency and cell wall porosity is supported by tests on various cell types, application of differently sized quenchers, and comparison of results with confocal, electron, and atomic force microscopy images. The quenching assay was used to investigate how changes in cell wall porosity affect the capability for extension growth in the model plant Arabidopsis thaliana Results suggest that increased porosity is not a precondition but a result of cell extension, thereby providing new insight on the mechanism plant organ growth. Furthermore, it was shown that higher cell wall porosity can facilitate the action of antifungal drugs in Saccharomyces cerevisiae , presumably by facilitating uptake., (© 2019 Liu et al.)

Pavement cells in the leaf epidermis of many plant species have intricate shapes that fit together much like the pieces of a jigsaw puzzle. They provide an accessible system to understand the development of complex cell shape. Since a protrusion in one cell must fit into the indentation in its neighbor, puzzle cells are also a good system to study how cell shape is coordinated across a plant tissue. Although molecular mechanisms have been proposed for both the patterning and coordination of puzzle cells, evidence is accumulating that mechanical and/or geometric cues may play a more significant role than previously thought., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Plant microtubules form a highly dynamic intracellular network with important roles for regulating cell division, cell proliferation, and cell morphology. Their organization and dynamics are co-ordinated by various microtubule-associated proteins (MAPs) that integrate environmental and developmental stimuli to fine-tune and adjust cytoskeletal arrays. IQ67 DOMAIN (IQD) proteins recently emerged as a class of plant-specific MAPs with largely unknown functions. Here, using a reverse genetics approach, we characterize Arabidopsis IQD5 in terms of its expression domains, subcellular localization, and biological functions. We show that IQD5 is expressed mostly in vegetative tissues, where it localizes to cortical microtubule arrays. Our phenotypic analysis of iqd5 loss-of-function lines reveals functions of IQD5 in pavement cell (PC) shape morphogenesis. Histochemical analysis of cell wall composition further suggests reduced rates of cellulose deposition in anticlinal cell walls, which correlate with reduced anisotropic expansion. Lastly, we demonstrate IQD5-dependent recruitment of calmodulin calcium sensors to cortical microtubule arrays and provide first evidence for important roles for calcium in regulation of PC morphogenesis. Our work identifies IQD5 as a novel player in PC shape regulation and, for the first time, links calcium signaling to developmental processes that regulate anisotropic growth in PCs.

Main Conclusion: The subfamily II catalytic subunits of protein phosphatase 2A (PP2A) regulate the cortical microtubule dynamics in Arabidopsis, through interaction with TONNEAU2 (TON2)/FASS and modulation of α-tubulin dephosphorylation. Protein phosphatase 2A is a major protein phosphatase in eukaryotes that dephosphorylates many different substrates to regulate their function. PP2A is assembled into a heterotrimeric complex of scaffolding A subunit, regulatory B subunit, and catalytic C subunit. Plant PP2A catalytic C subunit (PP2AC) isoforms are classified into two subfamilies. In this study, we investigated the cellular functions of the Arabidopsis PP2AC subfamily II genes PP2AC-3 and PP2AC-4, particularly regarding the cortical microtubule (MT) organization. PP2AC-3 and PP2AC-4 strongly interacted with the B'' regulatory subunit TON2. Simultaneous silencing of PP2AC-3 and PP2AC-4 by virus-induced gene silencing (PP2AC-3,4 VIGS) significantly altered plant morphology in Arabidopsis, increasing cell numbers in leaves and stems. The leaf epidermis of PP2AC-3,4 VIGS plants largely lost its jigsaw-puzzle shape and exhibited reduced trichome branch numbers. VIGS of PP2AC-3,4 in Arabidopsis transgenic plants that expressed GFP-fused β-tubulin 6 isoform (GFP-TUB6) for the visualization of MTs caused a reduction in the cortical MT array density in the pavement cells. VIGS of TON2 also led to similar cellular phenotypes and cortical MT patterns compared with those after VIGS of PP2AC-3,4, suggesting that PP2AC-3,4 and their interaction partner TON2 play a role in cortical MT organization in leaf epidermal cells. Furthermore, silencing of PP2AC-3,4 did not affect salt-induced phosphorylation of α-tubulin but delayed its dephosphorylation after salt removal. The reappearance of cortical MT arrays after salt removal was impaired in PP2AC-3,4 VIGS plants. These results suggest an involvement of PP2AC subfamily II in the regulation of cortical MT dynamics under normal and salt-stress conditions in Arabidopsis.

TRYPTICHON (TRY) and ENHANCER OF TRY AND CPC2 (ETC2) encode R3-type MYB transcription factors that are involved in epidermal cell differentiation in Arabidopsis thaliana. TRY and ETC2 belong to the CPC-like MYB gene family, which includes seven homolog genes. Previously, we showed that among the CPC family members, TRY and ETC2 are characterized by rapid proteolysis compared with that of other members, and we demonstrated that this proteolysis is mediated by the proteasome-dependent pathway. In this study, we compared the functions of the wild-type TRY and ETC2 proteins and their amino acid-substituted versions. Our results showed that the substitution of amino acids in the C-terminal of TRY and ETC2 conferred them the ability to induce root hair formation. Furthermore, we confirmed that these mutations enhanced the stability of the TRY and ETC2 proteins. These results revealed that the amino acids, which are important for the functions of TRY and ETC2, mediate morphological pattern formation and can be useful in understanding the pathway determining the fate of root hair cells., Competing Interests: The authors have declared that no competing interests exist.

Fast directional growth is a necessity for the young seedling; after germination, it needs to quickly penetrate the soil to begin its autotrophic life. In most dicot plants, this rapid escape is due to the anisotropic elongation of the hypocotyl, the columnar organ between the root and the shoot meristems. Anisotropic growth is common in plant organs and is canonically attributed to cell wall anisotropy produced by oriented cellulose fibers. Recently, a mechanism based on asymmetric pectin-based cell wall elasticity has been proposed. Here we present a harmonizing model for anisotropic growth control in the dark-grown Arabidopsis thaliana hypocotyl: basic anisotropic information is provided by cellulose orientation) and additive anisotropic information is provided by pectin-based elastic asymmetry in the epidermis. We quantitatively show that hypocotyl elongation is anisotropic starting at germination. We present experimental evidence for pectin biochemical differences and wall mechanics providing important growth regulation in the hypocotyl. Lastly, our in silico modelling experiments indicate an additive collaboration between pectin biochemistry and cellulose orientation in promoting anisotropic growth., Competing Interests: FB, YC, BB, JC, HJ, SB No competing interests declared, (© 2018, Bou Daher et al.)

Main Conclusion: Microcracks in the cuticle of developing apples are aligned with ridges on the inner cuticle surface and are indicative of stress-strain concentrations above the anticlinal cell walls. Microcracks occur in cuticles of most fruits. Growth strains are considered causal. In apples (Malus × domestica), microcracks usually form a mesh pattern similar to that formed by cuticular ridges. Ridge patterns are similar to those of the epidermal cells' anticlinal walls. Our aim was to identify the mechanistic bases for these pattern similarities. By quantifying ridge depth, ridge width, and the areas enclosed by ridges, we reveal the presence of major and minor ridges. Major ridges enclose two-to-four epidermal cells, minor ridges only one cell. There are similar and overlying patterns of microcracking on the cuticle's outer surface and of ridges on its inner surface-microcracks generally follow the outlines of the major ridges. In biaxial tensile tests at 20 kPa, strains were low and microcracks shallow, but at > 40 kPa, strains were higher and microcracks deeper. Microcracks traversing the cuticle are usually aligned with the anticlinal walls of the underlying epidermal cells. In general, increased skin strain is associated with increased skin transpiration. Transpiration increases are reversible for low strains but irreversible for high strains. The alignment of cuticular microcracks with the major ridges, and these with the anticlinal cell walls, indicates associated stress/strain concentrations.

In land plants, the aerial epidermis is essential for growth control, protection and environmental interactions. Epidermal cell fate is specified early during embryogenesis and maintained throughout plant life. Molecular actors of epidermal specification have been characterized, but how epidermal fate is maintained during growth remains unclear. DEFECTIVE KERNEL 1 (DEK1) is required for epidermal cell fate maintenance during both embryonic and post-embryonic plant development. The activation of a mechanosensitive Ca 2+ channel was recently shown to depend on DEK1, suggesting that the interpretation of mechanical cues could be critical for maintaining epidermal cell fate. Here, we integrate these findings into the epidermal specification network and propose a model explaining why epidermal specification may depend upon the sensing of epidermal tension., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

During secondary growth in most eudicots and gymnosperms, the periderm replaces the epidermis as the frontier tissue protecting the vasculature from biotic and abiotic stresses. Despite its importance, the mechanisms underlying periderm establishment and formation are largely unknown. The herbaceous Arabidopsis thaliana undergoes secondary growth, including periderm formation in the root and hypocotyl. Thus, we focused on these two organs to establish a framework to study periderm development in a model organism. We identified a set of characteristic developmental stages describing periderm growth from the first cell division in the pericycle to the shedding of the cortex and epidermis. We highlight that two independent mechanisms are involved in the loosening of the outer tissues as the endodermis undergoes programmed cell death, whereas the epidermis and the cortex are abscised. Moreover, the phellem of Arabidopsis, as in trees, is suberized, lignified and peels off. In addition, putative regulators from oak and potato are also expressed in the Arabidopsis periderm. Collectively, the periderm of Arabidopsis shares many characteristics/features of woody and tuberous periderms, rendering Arabidopsis thaliana an attractive model for cork biology., (© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.)

Glandular trichomes and cuticles are both specialized structures that cover the epidermis of aerial plant organs. The former are commonly regarded as 'biofactories' for producing valuable natural products. The latter are generally considered as natural barriers for defending plants against abiotic and biotic stresses. However, the regulatory network for their formation and relationship remains largely elusive. Here we identify a homeodomain-leucine zipper (HD-ZIP) IV transcription factor, AaHD8, directly promoting the expression of AaHD1 for glandular trichome initiation in Artemisia annua. We found that AaHD8 positively regulated leaf cuticle development in A. annua via controlling the expression of cuticle-related enzyme genes. Furthermore, AaHD8 interacted with a MIXTA-like protein AaMIXTA1, a positive regulator of trichome initiation and cuticle development, forming a regulatory complex and leading to enhanced transcriptional activity in regulating the expression of AaHD1 and cuticle development genes. Our results reveal a molecular mechanism by which a novel HD-ZIP IV/MIXTA complex plays a significant role in regulating epidermal development, including glandular trichome initiation and cuticle formation., (© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.)

The development and patterning of stomata in the plant epidermis has emerged as an ideal system for studying fundamental plant developmental processes. Over the past twenty years most studies of stomata have used the model dicotyledonous plant Arabidopsis thaliana. However, cultivated monocotyledonous grass (or Gramineae) varieties provide the majority of human nutrition, and future research into grass stomata could be of critical importance for improving food security. Recent studies using Brachypodium distachyon, Hordeum vulgare (barley) and Oryza sativa (rice) have led to the identification of the core transcriptional regulators essential for stomatal initiation and progression in grasses, and begun to unravel the role of secretory signaling peptides in controlling stomatal developmental. This review revisits how stomatal developmental unfolds in grasses, and identifies key ontogenetic steps for which knowledge of the underpinning molecular mechanisms remains outstanding., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Premise of the Study: In numerous vascular plants, pavement cells of the leaf epidermis are shaped like a jigsaw-puzzle piece. Knowledge about the subcellular pattern of growth that accompanies morphogenesis of such a complex shape is crucial for studies of the role of the cytoskeleton, cell wall and phytohormones in plant cell development. Because the detailed growth pattern of the anticlinal and periclinal cell walls remains unknown, our aim was to measure pavement cell growth at a subcellular resolution., Methods: Using fluorescent microbeads applied to the surface of the adaxial leaf epidermis of Arabidopsis thaliana as landmarks for growth computation, we directly assessed the growth rates for the outer periclinal and anticlinal cell walls at a subcellular scale., Key Results: We observed complementary tendencies in the growth pattern of the outer periclinal and anticlinal cell walls. Central portions of periclinal walls were characterized by relatively slow growth, while growth of the other wall portions was heterogeneous. Local growth of the periclinal walls accompanying lobe development after initiation was relatively fast and anisotropic, with maximal extension usually in the direction along the lobe axis. This growth pattern of the periclinal walls was complemented by the extension of the anticlinal walls, which was faster on the lobe sides than at the tips., Conclusions: Growth of the anticlinal and outer periclinal walls of leaf pavement cells is heterogeneous. The growth of the lobes resembles cell elongation via diffuse growth rather than tip growth., (© 2018 Botanical Society of America.)

The typical parameter used to evaluate the root growth response to gravity is the degree of root bending in time. This employs the quantification of the root tip angle toward gravity and, hence, does not directly assess the actual differential growth process. Here, we describe the cortical cell length as a parameter to quantify cell elongation during the gravitropic response, using median longitudinal confocal sections. This analysis depicts that root organ bending is a consequence of differential cellular elongation on the upper versus lower side of the gravistimulated root. Moreover, we introduce here a simple mounting setup that is suitable to gravistimulate and subsequently image seedlings on upright microscopes.

D'Arcy Thompson emphasised the importance of surface tension as a potential driving force in establishing cell shape and topology within tissues. Leaf epidermal pavement cells grow into jigsaw-piece shapes, highly deviating from such classical forms. We investigate the topology of developing Arabidopsis leaves composed solely of pavement cells. Image analysis of around 50,000 cells reveals a clear and unique topological signature, deviating from previously studied epidermal tissues. This topological distribution is established early during leaf development, already before the typical pavement cell shapes emerge, with topological homeostasis maintained throughout growth and unaltered between division and maturation zones. Simulating graph models, we identify a heuristic cellular division rule that reproduces the observed topology. Our parsimonious model predicts how and when cells effectively place their division plane with respect to their neighbours. We verify the predicted dynamics through in vivo tracking of 800 mitotic events, and conclude that the distinct topology is not a direct consequence of the jigsaw piece-like shape of the cells, but rather owes itself to a strongly life history-driven process, with limited impact from cell-surface mechanics., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

Successful fertilization relies on the production and effective release of viable pollen. Failure of anther opening (dehiscence), results in male sterility, although the pollen may be fully functional. MYB26 regulates the formation of secondary thickening in the anther endothecium, which is critical for anther dehiscence and fertility. Here, we show that although the MYB26 transcript shows expression in multiple floral organs, the MYB26 protein is localized specifically to the anther endothecium nuclei and that it directly regulates two NAC domain genes, NST1 and NST2 , which are critical for the induction of secondary thickening biosynthesis genes. However, there is a complex relationship of regulation between these genes and MYB26. Using DEX-inducible MYB26 lines and overexpression in the various mutant backgrounds, we have shown that MYB26 up-regulates both NST1 and NST2 expression. Surprisingly normal thickening and fertility rescue does not occur in the absence of MYB26, even with constitutively induced NST1 and NST2 , suggesting an additional essential role for MYB26 in this regulation. Combined overexpression of NST1 and NST2 in myb26 facilitates limited ectopic thickening in the anther epidermis, but not in the endothecium, and thus fails to rescue dehiscence. Therefore, by a series of regulatory controls through MYB26, NST1, NST2, secondary thickening is formed specifically within the endothecium; this specificity is essential for anther opening., (© 2017 American Society of Plant Biologists. All Rights Reserved.)

Background and Aims: Root absorptive characteristics rely on the presence of apoplastic barriers. However, little is known about the establishment of these barriers within a complex root system, particularly in a major portion of them - the lateral roots. In Zea mays L., the exodermis differentiates under the influence of growth conditions. Therefore, the species presents a suitable model to elucidate the cross-talk among environmental conditions, branching pattern and the maturation of barriers within a complex root system involved in the definition of the plant-soil interface. The study describes the extent to which lateral roots differentiate apoplastic barriers in response to changeable environmental conditions., Methods: The branching, permeability of the outer cell layers and differentiation of the endo- and exodermis were studied in primary roots and various laterals under different types of stress of agronomic importance (salinity, heavy metal toxicity, hypoxia, etc.). Histochemical methods, image analysis and apoplastic tracer assays were utilized., Key Results: The results show that the impact of growth conditions on the differentiation of both the endodermis and exodermis is modulated according to the type/diameter of the root. Fine laterals clearly represent that portion of a complex root system with a less advanced state of barrier differentiation, but with substantial ability to modify exodermis differentiation in response to environmental conditions. In addition, some degree of autonomy in exodermal establishment of Casparian bands (CBs) vs. suberin lamellae (SLs) was observed, as the absence of lignified exodermal CBs did not always fit with the lack of SLs., Conclusions: This study highlights the importance of lateral roots, and provides a first look into the developmental variations of apoplastic barriers within a complex root system. It emphasizes that branching and differentiation of barriers in fine laterals may substantially modulate the root system-rhizosphere interaction., (© The Author 2017. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com)

Mechanical information is an important contributor to cell polarity in uni- and multicellular systems [1-3]. In planar tissues like the Drosophila wing, cell polarity reorients during growth as cells divide and reorganize [4]. In another planar tissue, the Arabidopsis leaf epidermis [5], polarized, asymmetric divisions of stomatal stem cells (meristemoid mother cells [MMCs]) are fundamental for the generation and patterning of multiple cell types, including stomata. The activity of key transcription factors, polarizing factors [6], and peptide signals [7] explains some local stomatal patterns emerging from the behavior of a few lineally related cells [6, 8-11]. Here we demonstrate that, in addition to locally acting signals, tissue-wide mechanical forces can act as organizing cues, and that they do so by influencing the polarity of individual MMCs. If the mechanical stress environment in the tissue is altered through stretching or cell ablations, cellular polarity changes in response. In turn, polarity predicts the orientation of cellular and tissue outgrowth, leading to increased mechanical conflicts between neighboring cells. This interplay among growth, oriented divisions, and cell specification could contribute to the characteristic patterning of stomatal guard cells in the context of a growing leaf., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: The effect of the application of benzothiadiazole (BTH) and methyl jasmonate (MeJ) at veraison on the phenolic composition of grapes from three varieties (Monastrell, Syrah and Merlot) was studied during the ripening period, using HPLC techniques to measure flavonols, anthocyanins and tannins., Results: The effects of the treatments differed in the three varieties, and the maximum concentration of phenolic compounds was not always reached at the end of the ripening period but some days before harvest. At the end of ripening both treated Syrah grapes only differed from control grapes in the flavonol concentration, whereas MeJ-treated Merlot grapes presented higher anthocyanin and skin tannin contents than the control and BTH-treated grapes. Only the anthocyanin content was significantly higher in treated Monastrell grapes at the moment of harvest., Conclusion: The results indicate that the moment of elicitor treatment should be more studied since differences between treated and control grapes were, in general greater several days before harvest in all three varieties. © 2016 Society of Chemical Industry., (© 2016 Society of Chemical Industry.)

Background: Clonal selection is one of the tools used for grapevine improvement and therefore is very important for obtaining clones with better characteristics than the variety population. The aim of this study was to select superior grapevines of Vitis vinifera L. cv. Muscat Hamburg grown for fresh consumption., Results: The viticultural parameters and fruit composition of 35 selected vines were determined during a 5-year period. The evaluated parameters showed high variability among selected vines. The significant effect of vintage was observed for all descriptors with the exception of the number of seeds per berry and sugar concentration. Additionally, all vines were examined for their tolerance to low temperatures and the results showed 73% and 90% of primary bud injury at -20 and -25 °C, respectively. In relation to berry classification, the percentage of first-class grapes ranged from 60% to 69% for all selected grapevines. Multivariate statistical analysis was performed to classify grapevines based on their performance., Conclusion: Fourteen grapevines were identified as the most promising among the 35 vines initially planted, based on high yield, bunch and berry weight, sugar content and percentage of first-grade grapes. Those grapevines were selected for the next phase of the clonal selection. This study highlighted the importance of clonal selection for improvement of the variety population. © 2016 Society of Chemical Industry., (© 2016 Society of Chemical Industry.)

Background and Aims: It has been proposed that modification of leaf size, driven by epidermal cell size, balances leaf water supply (determined by veins) with transpirational demand (generated by stomata) during acclimation to local irradiance. We aimed to determine whether this is a general pattern among plant species with contrasting growth habits., Methods: We compared observed relationships between leaf minor vein density, stomatal density, epidermal cell size and leaf size in four pairs of herbs and woody species from the same families grown under sun and shade conditions with modelled relationships assuming vein and stomatal densities respond passively to epidermal cell expansion. Leaf lignin content was also quantified to assess whether construction costs of herbaceous leaf veins differ from those of woody plants and the leaf mass fraction invested in veins., Key Results: Modelled relationships accurately described observed relationships, indicating that in all species, co-ordinated changes to the density of minor veins and stomata were mediated by a common relationship between epidermal cell size, vein density and stomatal density, with little or no impact from stomatal index. This co-ordination was independent of changes in leaf size and is likely to be an adaptive process driven by the significant proportion of biomass invested in veins (13·1 % of sun leaf dry weight and 21·7 % of shade leaf dry weight). Relative costs of venation increased in the shade, intensifying selective pressure towards economizing investment in vein density., Conclusions: Modulation of epidermal cell size appears to be a general mechanism among our experimental species to maintain a constant ratio between leaf anatomical traits that control leaf water fluxes independently of habit. We propose that this process may co-ordinate plasticity in hydraulic supply and demand in the majority of eudicot angiosperms., (© The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: The anthocyanin and tannin concentration and composition of Vitis vinifera L. cv. Sangiovese berries were investigated from post-veraison to harvest. Exhaustive extraction with methanol and acetone was performed to determine the total flavonoid concentration, while a model hydroalcoholic solution was used to prepare extracts representing the winemaking process. The aim of this study was to improve the knowledge of the phenolic maturity of Sangiovese grape., Results: The total anthocyanin concentration increased during ripening, but the quantity of extractable anthocyanins increased more rapidly than the total. The total skin tannin concentration declined from post-veraison to harvest, whereas the extractable portion increased, with little difference in the composition of the fractions. Both the total and extractable seed tannin concentration diminished rapidly just after veraison, and only small fluctuations were detected until harvest., Conclusion: These results indicate that the extractability of anthocyanins and skin tannins increases during ripening, whereas there is no clear trend for seed tannins during the same period. This is the first survey to study the behavior of phenolic compounds during different steps of ripening of Sangiovese grape. © 2016 Society of Chemical Industry., (© 2016 Society of Chemical Industry.)

Premise of the Study: The Arabidopsis MYB transcriptional factors FOUR LIPS (FLP) and MYB88 are predicted to play a broader role than just limiting the number of guard cells per stoma in the epidermis based on their expression patterns. Analysis of the numbers of all epidermal cells in cotyledons in flp mutants and the flp-1 myb88 double mutant may substantiate the functions of FLP and MYB88 in nonstomatal epidermal cells., Methods: The number of all types of abaxial epidermal cells in mature cotyledons were determined under different growth conditions in flp-1, flp-3, flp-8, and tmm-1 single mutants, flp-1 tmm-1 and flp-1 myb88 double mutants, and accessions Columbia-0 (Col, control for flp-1, flp-3, and flp-1 myb88) and Landsberg erecta (Ler, control for flp-8)., Key Results: In soil-grown plants, the number of pavement cells and meristemoids per cotyledon were not statistically different between the flp mutants and their respective controls and between flp-1 and flp-1 myb88, except sometimes for the number of meristemoids or pavement cells between flp-1 and Col. In contrast, the same comparisons yielded statistically significant differences in medium-grown plants, i.e., more cells in the flp mutants and flp-1 myb88, except for meristemoids between flp-8 and Ler and pavement cells between flp-1 and flp-1 myb88. No significant difference was detected for nonstomatal epidermal cells between tmm-1 and flp-1/tmm-1 under the two conditions., Conclusions: FLP and MYB88 inhibit the production of nonstomatal epidermal cells largely in a growth-condition-dependent manner. The tmm-1 mutation is epistatic to the flp-1 mutation in the production of nonstomatal epidermal cells in the cotyledon., (© 2016 Botanical Society of America.)

Filamentous actins (F-actins) play a vital role in epidermal cell morphogenesis. However, a limited number of studies have examined actin-dependent leaf epidermal cell morphogenesis events in rice. In this study, two recessive mutants were isolated: less pronounced lobe epidermal cell2-1 (lpl2-1) and lpl3-1, whose leaf and stem epidermis developed a smooth surface, with fewer serrated pavement cell (PC) lobes, and decreased papillae. The lpl2-1 also exhibited irregular stomata patterns, reduced plant height, and short panicles and roots. Molecular genetic studies demonstrated that LPL2 and LPL3 encode the PIROGI/Specifically Rac1-associated protein 1 (PIR/SRA1)-like and NCK-associated protein 1 (NAP1)-like proteins, respectively, two components of the suppressor of cAMP receptor/Wiskott-Aldrich syndrome protein-family verprolin-homologous protein (SCAR/WAVE) regulatory complex involved in actin nucleation and function. Epidermal cells exhibited abnormal arrangement of F-actins in both lpl2 and lpl3 expanding leaves. Moreover, the distorted trichomes of Arabidopsis pir could be partially restored by an overexpression of LPL2 A yeast two-hybrid assay revealed that LPL2 can directly interact with LPL3 in vitro Collectively, the results indicate that LPL2 and LPL3 are two functionally conserved homologs of the SCAR/WAVE complex components, and that they play an important role in controlling epidermal cell morphogenesis in rice by organising F-actin., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Main Conclusions: Deletion of the ancestral gene of the land plant multigene family of receptor like kinase CR4 in Physcomitrella patens demonstrates involvement in developmental control of gametophytic and sporophytic organs. The CRINKLY4 (CR4) family of receptor kinases in angiosperms consists of three clades, one including CR4, the CR4-related CCR1 and CCR2, a second including CCR3 and CCR4 family members, and a third and more distant clade. In addition to crinkly leaves in maize, which gave rise to the mutant gene name, CR4 is implicated in ovule, embryo, flower and root development in Arabidopsis thaliana. In root tips of the same species the module including a CLAVATA3/ESR-related protein, an Arabidopsis CR4, a CLAVATA1 and a WUSCHEL-related homeobox 5 (CLE40-ACR4-CLV1-WOX5) is implicated in meristem cell regulation. In embryos and shoots, CR4 acts together with A. thaliana MERISTEM LAYER 1 and PROTODERMAL FACTOR 2 to promote A. thaliana epidermis differentiation. Phylogenetic analysis has demonstrated that early land plants, e.g. mosses carry a single ancestral CR4 gene, together with genes encoding the other members of the CLE40-ACR4-CLV1-WOX5 signaling module. Here we show that CR4 serves as a broad regulator of morphogenesis both in gametophyte phyllids, archegonia and in sporophyte epidermis of the moss Physcomitrella patens. The phenotype of the CR4 deletion mutant in moss provides insight into the role of the ancestral CR4 gene as a regulator of development in early land plants.

Plant leaf epidermal cells exhibit a jigsaw puzzle-like pattern that is generated by interdigitation of the cell wall during leaf development. The contribution of two ROP GTPases, ROP2 and ROP6, to the cytoskeletal dynamics that regulate epidermal cell wall interdigitation has already been examined; however, how interactions between these molecules result in pattern formation remains to be elucidated. Here, we propose a simple interface equation model that incorporates both the cell wall remodeling activity of ROP GTPases and the diffusible signaling molecules by which they are regulated. This model successfully reproduces pattern formation observed in vivo, and explains the counterintuitive experimental results of decreased cellulose production and increased thickness. Our model also reproduces the dynamics of three-way cell wall junctions. Therefore, this model provides a possible mechanism for cell wall interdigitation formation in vivo.

Growth and developmental processes are occasionally accompanied by multiple rounds of DNA replication, known as endoreduplication. Coordination between endoreduplication and cell size regulation often plays a crucial role in proper organogenesis and cell differentiation. Here, we report that the level of correlation between ploidy and cell volume is different in the outer and inner cell layers of leaves of Arabidopsis thaliana using a novel imaging technique. Although there is a well-known, strong correlation between ploidy and cell volume in pavement cells of the epidermis, this correlation was extremely weak in palisade mesophyll cells. Induction of epidermis cell identity based on the expression of the homeobox gene ATML1 in mesophyll cells enhanced the level of correlation between ploidy and cell volume to near that of wild-type epidermal cells. We therefore propose that the correlation between ploidy and cell volume is regulated by cell identity., (© 2016. Published by The Company of Biologists Ltd.)

Inheritance of epidermis pigmentation in the pericarp of sunflower seeds was studied. Inheritance of pigmentation was confirmed by three alleles Ew (epidermis devoid of pigmentation), Estr (epidermal pigmentation in strips), Edg (solid pigmentation). Dominance of the lack of epidermis pigmentation over striped epidermis and striped epidermis over solid pigmentation was established. It was shown that the striped epidermis pigmentation and the presence of testa layer are controlled by two genes, expression of which is independent from each other. Yellowish hypodermis was discovered in the sample I2K2218, which is inherited monogenically dominantly.

Root anatomy, cytoskeleton orientation and cell wall thickness in cells of the roots formed de novo in vitro under clinorotation (simulated microgravity) were investigated. Structure of the embryonic roots and of the roots formed de novo in cambium cells of the leaf petiole explants was shown to be similar. Root cell differentiation in vitro under clinorotation did not differ from that in control. Changes of tubulin microtubules' orientation in the epidermis of the distal elongation zone were observed under clinorotation that seems to be associated with specific physiological properties of the cells. Under clinorotation, the tendency of cell wall thinning was detected in the root cells formed in vitro.

The epidermis plays a pivotal role in plant development and interaction with the environment. However, it is still poorly understood, especially its outer epidermal wall: a singular wall covered by a cuticle. Changes in the cuticle and cell wall structures are important to fully understand their functions. In this work, an ultrastructure and immunocytochemical approach was taken to identify changes in the cuticle and the main components of the epidermal cell wall during tomato fruit development. A thin and uniform procuticle was already present before fruit set. During cell division, the inner side of the procuticle showed a globular structure with vesicle-like particles in the cell wall close to the cuticle. Transition between cell division and elongation was accompanied by a dramatic increase in cuticle thickness, which represented more than half of the outer epidermal wall, and the lamellate arrangement of the non-cutinized cell wall. Changes in this non-cutinized outer wall during development showed specific features not shared with other cell walls. The coordinated nature of the changes observed in the cuticle and the epidermal cell wall indicate a deep interaction between these two supramolecular structures. Hence, the cuticle should be interpreted within the context of the outer epidermal wall., (© 2016 American Society of Plant Biologists. All Rights Reserved.)