Periderm Development Research Articles

Rhytidome- and cork-type barks of holm oak, cork oak and their hybrids highlight processes leading to cork formation

BackgroundThe periderm is basic for land plants due to its protective role during radial growth, which is achieved by the polymers deposited in the cell walls. In most trees, like holm oak, the first periderm is frequently replaced by subsequent internal periderms yielding a heterogeneous outer bark made of a mixture of periderms and phloem tissues, known as rhytidome. Exceptionally, cork oak forms a persistent or long-lived periderm which results in a homogeneous outer bark of thick phellem cell layers known as cork. Cork oak and holm oak distribution ranges overlap to a great extent, and they often share stands, where they can hybridize and produce offspring showing a rhytidome-type bark.ResultsHere we use the outer bark of cork oak, holm oak, and their natural hybrids to analyse the chemical composition, the anatomy and the transcriptome, and further understand the mechanisms underlying periderm development. We also include a unique natural hybrid individual corresponding to a backcross with cork oak that, interestingly, shows a cork-type bark. The inclusion of hybrid samples showing rhytidome-type and cork-type barks is valuable to approach cork and rhytidome development, allowing an accurate identification of candidate genes and processes. The present study underscores that abiotic stress and cell death are enhanced in rhytidome-type barks whereas lipid metabolism and cell cycle are enriched in cork-type barks. Development-related DEGs showing the highest expression, highlight cell division, cell expansion, and cell differentiation as key processes leading to cork or rhytidome-type barks.ConclusionTranscriptome results, in agreement with anatomical and chemical analyses, show that rhytidome and cork-type barks are active in periderm development, and suberin and lignin deposition. Development and cell wall-related DEGs suggest that cell division and expansion are upregulated in cork-type barks whereas cell differentiation is enhanced in rhytidome-type barks.

The application of zebrafish model in the study of cleft lip and palate development: A systematic review

ObjectiveCraniofacial growth and development are more than a scientific curiosity; it is of tremendous interest to clinicians. Insights into the genetic etiology of cleft lip and palate development are essential for improving diagnosis and treatment planning. The purpose of this systematic review was to utilize a zebrafish model to highlight the role of the IRF6 gene in cleft lip and palate development in humans. DataThis review adhered to the guidelines outlined in the PRISMA statement. Nine studies were included in the analysis. SourcesThis study used major scientific databases such as MEDLINE, EMBASE, Web of Science, and the Zebrafish Information Network and yielded 1275 articles. Two reviewers performed the screening using COVIDENCE™ independently, and a third reviewer resolved any conflicts. Study selectionAfter applying the inclusion and exclusion criteria and screening, nine studies were included in the analysis. The Systematic Review Center for Laboratory Animal Experimentation's (SYRCLE's) risk-of-bias tool was used to assess the quality of the included studies. ResultsThe main outcome supports the role of the IRF6 gene in zebrafish periderm development and embryogenesis, and IRF6 variations result in cleft lip and palate development. The overall SYRCLE risk of bias was low-medium. ConclusionIn conclusion, this review indicated the critical role of the IRF6 gene and its downstream genes (GRHL3, KLF17, and ESRP1/2) in the development of cleft lip and palate in zebrafish models. Genetic mutation zebrafish models provide a high level of insights into zebrafish craniofacial development. Clinical relevancethis review provides a productive avenue for understanding the powerful and conserved zebrafish model for investigating the pathogenesis of human cleft lip and palate.

Plant periderm as a continuum in structural organisation: a tracheophyte-wide survey and hypotheses on evolution.

Periderm is a well-known structural feature with vital roles in protection of inner plant tissues and wound healing. Despite its importance to plant survival, knowledge of periderm occurrences outside the seed plants is limited and the evolutionary origins of periderm remain poorly explored. Here, we review the current knowledge of the taxonomic distribution of periderm in its two main forms - canonical periderm (periderm formed as a typical ontogenetic stage) and wound periderm (periderm produced as a self-repair mechanism) - with a focus on major plant lineages, living and extinct. We supplement the published occurrences with data based on our own observations and experiments. This updated body of data reveals that the distribution of wound periderm is more widespread taxonomically than previously recognized and some living and extinct groups are capable of producing wound periderm, despite canonical periderm being absent from their normal developmental program. A critical review of canonical and wound periderms in extant and fossil lineages indicates that not all periderms are created equal. Their organisation is widely variable and the differences can be characterised in terms of variations in three structural features: (i) the consistency in orientation of periclinal walls within individual files of periderm cells; (ii) the lateral coordination of periclinal walls between adjacent cell files; and (iii) whether a cambial layer and conspicuous layering of inward and outward derivatives can be distinguished. Using a new system of scoring periderm structure based on these criteria, we characterise the level of organisation of canonical and wound periderms in different lineages. Looking at periderms through the lens provided by their level of organisation reveals that the traditional image of periderm as a single generalised feature, is best viewed as a continuum of structural configurations that are all predicated by the same basic process (periclinal divisions), but can fall anywhere between very loosely organized (diffuse periclinal growth) to very tightly coordinated (organized periclinal growth). Overall, wound periderms in both seed plants and seed-free plants have lower degrees of organisation than canonical periderms, which may be due to their initiation in response to inherently disruptive traumatic events. Wound and canonical periderms of seed plants have higher degrees of organisation than those of seed-free plants, possibly due to co-option of the programs responsible for organizing their vascular cambial growth. Given the importance of wound periderm to plant survival, its widespread taxonomic distribution, and its early occurrence in the fossil record, we hypothesise that wound periderm may have had a single origin in euphyllophytes and canonical periderm may have originated separately in different lineages by co-option of the basic regulatory toolkit of wound periderm formation. In one evolutionary scenario, wound periderm regulators activated initially by tissue tearing due to tensional stresses elicited by woody growth underwent heterochronic change that switched their activation trigger from tissue tearing to the tensional stresses that precede it, with corresponding changes in the signalling that triggered the regulatory cascade of periderm development from tearing-induced signals to signalling induced by tension in cells.

PAT (Periderm Assessment Toolkit): A Quantitative and Large-Scale Screening Method for Periderm Measurements.

The periderm is a vital protective tissue found in the roots, stems, and woody elements of diverse plant species. It plays an important function in these plants by assuming the role of the epidermis as the outermost layer. Despite its critical role for protecting plants from environmental stresses and pathogens, research on root periderm development has been limited due to its late formation during root development, its presence only in mature root regions, and its impermeability. One of the most straightforward measurements for comparing periderm formation between different genotypes and treatments is periderm (phellem) length. We have developed PAT (Periderm Assessment Toolkit), a high-throughput user-friendly pipeline that integrates an efficient staining protocol, automated imaging, and a deep-learning-based image analysis approach to accurately detect and measure periderm length in the roots of Arabidopsis thaliana. The reliability and reproducibility of our method was evaluated using a diverse set of 20 Arabidopsis natural accessions. Our automated measurements exhibited a strong correlation with human-expert-generated measurements, achieving a 94% efficiency in periderm length quantification. This robust PAT pipeline streamlines large-scale periderm measurements, thereby being able to facilitate comprehensive genetic studies and screens. Although PAT proves highly effective with automated digital microscopes in Arabidopsis roots, its application may pose challenges with nonautomated microscopy. Although the workflow and principles could be adapted for other plant species, additional optimization would be necessary. While we show that periderm length can be used to distinguish a mutant impaired in periderm development from wild type, we also find it is a plastic trait. Therefore, care must be taken to include sufficient repeats and controls, to minimize variation, and to ensure comparability of periderm length measurements between different genotypes and growth conditions.

Cell wall response of field grown Populus to Septoria infection.

Due to its ability to spread quickly and result in tree mortality, Sphaerulina musiva (Septoria) is one of the most severe diseases impacting Populus. Previous studies have identified that Septoria infection induces differential expression of phenylpropanoid biosynthesis genes. However, more extensive characterization of changes to lignin in response to Septoria infection is lacking. To study the changes of lignin due to Septoria infection, four field grown, naturally variant Populus trichocarpa exhibiting visible signs of Septoria infection were sampled at health, infected, and reaction zone regions for cell wall characterization. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and acid hydrolysis were applied to identify changes to the cell wall, and especially lignin. FTIR and subsequent principal component analysis revealed that infected and reaction zone regions were similar and could be distinguished from the non-infected (healthy) region. NMR results indicated the general trend that infected region had a higher syringyl:guaiacyl ratio and lower p-hydroxybenzoate content than the healthy regions from the same genotype. Finally, Klason lignin content in the infected and/or reaction zone regions was shown to be higher than healthy region, which is consistent with previous observations of periderm development and metabolite profiling. These results provide insights on the response of Populus wood characteristics to Septoria infection, especially between healthy and infected region within the same genotype.

Multi-omics analysis of green- and russet skin pear cultivars identify key regulators of skin russeting

Different periderm development makes the partial and full russet skin of pear fruit, which negatively influence pear fruit appearance quality. The switch gene for russet skin formation and the functional conservation of the homologs among different species showed to have multiple significance to clarify the transcriptional network underlying russet skin formation. In this study, two pear cultivars coupled with their mutants were used to explore the underlying molecular regulatory network of russet skin formation. RNA-sequencing and metabolomics were used to identify the key pathways and switch genes involved in russet skin formation, and identified genes involved in lignin biosynthesis, suberin biosynthesis, and suberin transporters. Additionally, a set of transcription factors was identified via coexpression network analysis and differential expression analysis, including PbMYB308, PbbHLH49, PbWRKY24, and PbNAC40, which had a high correlation with russet skin-related genes. These genes were predicted as putative regulators involved in russet pear skin formation. qRT–PCR was performed to validate the transcriptome data. Two varieties and their mutants were used for the first time to explore the switch genes and underlying mechanisms of russet formation. We concentrated on the russet skin development in pear fruit, with an emphasis on exploring the underlying regulatory mechanisms.

Complex wound response mechanisms and phellogen evolution - insights from Early Devonian euphyllophytes.

We analyze the oldest fossil occurrences of wound-response periderm to characterize the development of wound responses in early tracheophytes. The origin of periderm production by a cambium (phellogen), an innovation with key roles in protection of inner plant tissues, is poorly explored; understanding periderm development in early tracheophytes can illuminate key aspects of this process. Anatomy of wound-response tissues is characterized in serial sections in a new Early Devonian (Emsian; c. 400 Ma) euphyllophyte from Quebec (Canada) - Nebuloxyla mikmaqiana sp. nov. - and compared to previously described euphyllophyte periderm from the same fossil locality to reconstruct periderm development. Characterizing development in these oldest periderm occurrences allows us to propose a model for the development of wound-response periderm in early tracheophytes: by phellogen activity that is poorly coordinated laterally but bifacial, producing secondary tissues initially outwardly and subsequently inwardly. The earliest occurrences of wound periderm pre-date the oldest known periderm produced systemically as a regular ontogenetic stage (canonical periderm), suggesting that periderm evolved initially as a wound-response mechanism. We hypothesize that canonical periderm evolved by exaptation of this wound sealing mechanism, whose deployment was triggered by tangential tensional stresses induced in the superficial tissues by vascular cambial growth from within.

Solving the regulation puzzle of periderm development using advances in fruit skin.

Periderm protects enlarged organs of most dicots and gymnosperms as a barrier to water loss and disease invasion during their secondary growth. Its development undergoes a complex process with genetically controlled and environmental stress-induced characters. Different development of periderm makes the full and partial russet of fruit skin, which diverges in inheritance with qualitative and quantitative characters, respectively, in pear pome. In addition to its specific genetics, fruit periderm has similar development and structure as that of stem and other organs, making it an appropriate material for periderm research. Recently, progress in histochemical as well as transcriptome and proteome analyses, and quantitative trait locus (QTL) mapping have revealed the regulatory molecular mechanism in the periderm based on the identification of switch genes. In this review, we concentrate on the periderm development, propose the conservation of periderm regulation between fruit and other plant organs based on their morphological and molecular characteristics, and summarize a regulatory network with the elicitors and repressors for the tissue development. Spontaneous programmed-cell death (PCD) or environmental stress produces the original signal that triggers the development of periderm. Spatio-temporal specific PCD produced by PyPPCD1 gene and its homologs can play a key role in the coordinated regulation of cell death related tissue development.

Potato Periderm Development and Tuber Skin Quality.

The periderm is a corky tissue that replaces the epidermis when the latter is damaged, and is critical for preventing pathogen invasion and water loss. The periderm is formed through the meristematic activity of phellogen cells (cork cambium). The potato skin (phellem cells) composes the outer layers of the tuber periderm and is a model for studying cork development. Early in tuber development and following tuber expansion, the phellogen becomes active and produces the skin. New skin layers are continuously added by division of the phellogen cells until tuber maturation. Some physiological disorders of the potato tuber are related to abnormal development of the skin, including skinning injuries and russeting of smooth-skinned potatoes. Thus, characterizing the potato periderm contributes to modeling cork development in plants and helps to resolve critical agricultural problems. Here, we summarize the data available on potato periderm formation, highlighting tissue characteristics rather than the suberization processes.

An ARF1-binding factor triggering programmed cell death and periderm development in pear russet fruit skin.

Plants have a cuticular membrane (CM) and periderm membrane (PM), which act as barriers to terrestrial stresses. The CM covers primary organs with a continuous hydrophobic layer of waxes embedded in cutin, while the PM includes suberized cells stacked externally to the secondary tissues. The formation of native periderm is regulated by a postembryonic meristem phellogen that produces suberized phellem (cork) outwardly. However, the mechanism controlling phellogen differentiation to phellem remains to be clarified. Here, map-based cloning in a pear F1 population with segregation for periderm development in fruit skin facilitated the identification of an aspartic acid repeat deletion in Pyrus Periderm Programmed Cell Death 1.1 (PyPPCD1.1) that triggers phellogen activity for cork formation in russet fruit skin of pear. PyPPCD1.1 showed preferential expression in pear fruit skin, and the encoded protein shares a structural similarity to that of the viral capsid proteins. Aspartic acid deletion in PyPPCD1.1 weakened its nuclear localization but increased its accumulation in the chloroplast. The products of both PyPPCD1.1 and its recessive allele directly interact with ADP-ribosylation factor 1 (ARF1). PyPPCD1.1 triggered programmed cell death in an ARF1-dependent manner. Thus, this study identified the switch gene for programmed cell death and periderm development and provided a new molecular regulatory mechanism underlying the development of this trait.

The Making of Plant Armor: The Periderm.

The periderm acts as armor protecting the plant's inner tissues from biotic and abiotic stress. It forms during the radial thickening of plant organs such as stems and roots and replaces the function of primary protective tissues such as the epidermis and the endodermis. A wound periderm also forms to heal and protect injured tissues. The periderm comprises a meristematic tissue called the phellogen, or cork cambium, and its derivatives: the lignosuberized phellem and the phelloderm. Research on the periderm has mainly focused on the chemical composition of the phellem due to its relevance as a raw material for industrial processes. Today, there is increasing interest in the regulatory network underlying periderm development as a novel breeding trait to improve plant resilience and to sequester CO2. Here, we discuss our current understanding of periderm formation, focusing on aspects of periderm evolution, mechanisms of periderm ontogenesis, regulatory networks underlying phellogen initiation and cork differentiation, and future challenges of periderm research.

Van der woude syndrome

Orofacial clefts (OFCs) are the most common craniofacial birth defect in all populations worldwide and include cleft lip with or without cleft palate (CL/P) and cleft palate alone (CP). Approximately 70% of OFC are non syndromic while 30 % are syndromic. Syndromic OFCs are often caused by structural chromosomal anomalies or by coding mutations in a single gene. The most common OFC syndrome is Van der Woude syndrome (VWS, MIM #119300) which has 2% of all OFCs with an overall prevalence of 1/35,000-1/100,000 live births. The characteristic features of Van der Woude syndrome are orofacial clefts and congenital lower lip pits. IRF6 or GRHL3 plays an important role in VWS mutations. Van der Woude syndrome is inherited in an autosomal dominant pattern, mostly an affected person has one parent with the condition. Patients with Van der Woude Syndrome who has OFCs increased the risk of delayed language development, learning disabilities, or other mild cognitive problems. The average IQ of individuals with van der Woude syndrome is not significantly different. IRF6 or GRHL3 plays an important role in VWS mutations. The IRF6 protein is active in cells that give rise to tissues in the head and face. A shortage of the IRF6 protein affects the development and maturation of tissues in the face, resulting in the signs and symptoms of van der Woude syndrome such as OFCs. GRHL3 were shown to be required for the development of the periderm, and an important player in the IRF6 dependent pathway of periderm development. In this review, author will explain further about Van der Woude Syndrome and review the literature available on recent studies toward the caused of Van der Woude Syndrome whether it is developed from IRF6 genes.

Potato Periderm is the First Layer of Defence against Biotic and Abiotic Stresses: a Review

The frequently changing climate has resulted in plants facing more biotic and abiotic stresses than ever before, leading to yield and quality losses. The global population is increasing at an alarming rate and feeding the world has become a huge challenge. Being a staple crop of many countries, potato can help to overcome this challenge. A comprehensive knowledge of physiology, biochemistry and molecular genetics of development and wound healing of potato tuber periderm (skin) is very important as the periderm protects the tubers from skinning injuries, dehydration, bruising and biotic and abiotic stresses. Improvements in tuber periderm are essential to enhance tuber quality and shelf life and reduce financial losses. In this paper, we have reviewed the protective roles of tuber periderm layer in response to stress and injuries. Moreover, molecular regulation of native and wound-induced periderm formation has been discussed. Since suberization is an important aspect of tuber periderm formation and wound healing, we have also reviewed the key genes involved in this process. This review will pave the way for obtaining potato tubers resistant to various abiotic and pathogenic stresses.

Genome-wide Analyses Identify a Novel Risk Locus for Nonsyndromic Cleft Palate

The 3 major subphenotypes observed in patients with nonsyndromic orofacial clefts (NSOFCs) are nonsyndromic cleft lip only (NSCLO), nonsyndromic cleft lip with palate (NSCLP), and nonsyndromic cleft palate only (NSCPO). However, the genetic architecture underlying NSCPO is largely unknown. Here we performed a 2-stage genome-wide association study (GWAS) on NSCPO and replication analyses of selected variants in other NSOFCs from the Chinese Han population. We identified a novel locus (15q24.3) and a known locus (1q32.2) where variants in or near the gene reached genome-wide significance (2.80 × 10−13 < P < 1.72 × 10−08) in a test for association with NSCPO in a case-control design. Although a variant from 15q24.3 was found to be significantly associated with both NSCPO and NSCLP, the direction of estimated effects on risk were opposite. Our functional annotation of the risk alleles within 15q24.3 coupled with previously established roles of the candidate genes within identified risk loci in periderm development, embryonic patterning, and/or regulation of cellular processes supports their involvement in palate development and the pathogenesis of cleft palate. Our study advances the understanding of the genetic basis of NSOFCs and provides novel insights into the pathogenesis of NSCPO.

Anatomical Characteristics of Sunlight-induced Bark (Periderm) Coverages on Columnar Cacti of Central Mexico

More than twenty-three species of tall, long-lived columnar cacti from a large variety of locations within the Americas show sunlight-induced periderm development on their stems. Periderm coverages lead to cactus morbidity and mortality. Our objective was to determine if periderm coverage patterns and anatomical characteristics of periderm formation differ among five cactus species located at a single site. Periderm coverages, patterns of periderm coverages and histological changes during the periderm formation process were determined for five native species of tall, long-lived columnar cacti in the Tehuac&amp;aacute;n Valley of Puebla, Mexico during May to June 2019. Periderm coverages and patterns of periderm on cactus surface varied among the species. On surfaces, some species had periderm form at crests initially, while one species had initial periderm form where troughs join. All species had the same internal tissues but the characteristics of these tissues varied among species. In response to periderm formation, one species retained its cuticle while one species retained its hypodermis intact and another produced cork cells inside the hypodermis. Overall, the histological changes that result from periderm formation were specific for each species and no pair of species showed the same responses to periderm formation. In conjunction with data from species from South America, eight distinct scenarios of histological manifestations were documented. Although, each of the five cactus species were in the same location and received the same amount of sunlight exposures, each species showed unique periderm coverages on surfaces, unique anatomical characteristics and unique anatomical responses. Thus, location was not the primary determinant of responses.

Buds of “Italia melhorada” grapevines grown under tropical conditions develop a quiescent state

A double cropping system for the grapevine (Vitis vinifera L) has been commercially adopted for use in regions where the tropical climate is characterized by high temperatures and small variations in daylength throughout the year. Under these climatic conditions, the use of hydrogen cyanamide (HC), a compound that breaks bud dormancy, is mandatory to produce homogeneous budbreak. However, it is unknown whether grapevine buds are capable of developing endodormancy (ED) under these climatic conditions. In this study, typical signals of ED, such as the number of nodes per cane, the development of periderm and the thickening of the cell wall of the bud meristematic cells, were analysed in vines of “Italia melhorada” grown in Mossoró, Brazil (5°12′16″S), under a natural (ND) photoperiod (12/12 h), a short-day (SD) photoperiod (10/14 h) and a long-day (LD) photoperiod (14/10 h). The abundance of phytochrome A (VvPHYA) and B (VvPHYB) and FLOWERING LOCUS T (VvFT) transcripts in the leaves and buds was also determined. The results showed a reduced number of nodes per cane and development of the periderm in the shoots of grapevines grown under ND and SD photoperiods. In addition, compared with that under the LD photoperiod, the expression of VvPHYA and VvFT under the ND and SD-photoperiod decreased, and the expression of VvPHYB increased. However, the thickness of the cell wall of the bud meristematic cells increased only in the grapevines exposed to the SD photoperiod. Therefore, we hypothesize that cell wall thickening is a characteristic of ED, while decreased expression of VvPHYA and VvFT and increased expression of VvPHYB are characteristic of quiescence. Consequently, under a tropical conditions, the grapevine buds would be in a quiescent state and not in a dormant state.

Identification of regulatory elements recapitulating early expression of L-plastin in the zebrafish enveloping layer and embryonic periderm

We have cloned and characterized an intronic fragment of zebrafish lymphocyte cytosolic protein 1 (lcp1, also called L-plastin) that drives expression to the zebrafish enveloping layer (EVL). L-plastin is a calcium-dependent actin-bundling protein belonging to the plastin/fimbrin family of proteins, and is necessary for the proper migration and attachment of several adult cell types, including leukocytes and osteoclasts. However, in zebrafish lcp1 is abundantly expressed much earlier, during differentiation of the EVL. The cells of this epithelial layer migrate collectively, spreading vegetally over the yolk. L-plastin expression persists into the larval periderm, a transient epithelial tissue that forms the first larval skin. This finding establishes that L-plastin is activated in two different embryonic waves, with a distinct regulatory switch between the early EVL and the later leukocyte. To better study L-plastin expressing cells we attempted CRISPR/Cas9 homology-driven recombination (HDR) to insert a self-cleaving peptide (Cre-P2A-EGFP-CAAX) downstream of the native lcp1 promoter. This produced a stable zebrafish line expressing Cre recombinase in EVL nuclei and green fluorescence in EVL cell membranes. In vivo tracking of these labeled cells provided enhanced views of EVL migration behavior, membrane extensions, and mitotic events. Finally, we experimentally dissected key elements of the targeted lcp1 locus, discovering a ∼300 bp intronic sequence sufficient to drive EVL expression. The lcp1: Cre-P2A-EGFP-CAAX zebrafish should be useful for studying enveloping layer specification, gastrulation movements and periderm development in this widely used vertebrate model. In addition, the conserved regulatory sequences we have isolated predict that L-plastin orthologs may have a similar early expression pattern in other vertebrate embryos.

Influence of cambial age on the bark structure of Douglas-fir

Douglas-fir (Pseudotsuga menziesii) is a valuable conifer timber species. It has a thick bark with a high proportion of cork in the rhytidome that allows considering its recovery. This study focuses on the characterization of the bark features and their variation with cambial age along the stem using samples of 20 trees from two sites in Portugal at harvest for the sawmilling industry. The morphology and anatomical features of bark were examined including a detailed analysis of the arrangement of tissues, cell biometry, tissue proportion of the phloem, and the development of the rhytidome. Bark structure varied within the tree with cambial age at various height levels, and differences concerned mostly the rhytidome and periderm development, tissue morphology and disarray in the non-conducting phloem. A relationship between cell dimension, proportion of tissues in the phloem and age was observed; the effect of stem height position was statistically significant for sieve cell length, fiber–sclereid length and wall thickness with a decrease from the base to the top. The rhytidome thickness increased with cambial age: At the stem base (45–50 years of cambial age), the bark includes a rhytidome of about 3 cm thickness corresponding to 84% of the bark, with 5–8 periderms, containing nearly 50% of cork. The cork cells were thin-walled and oriented in radial rows, and the occurrence of thick-walled lignified cells was associated with the increments of the phellem layer. In the youngest periderm, the occurrence of phellem cells with empty lumens and thin suberized walls started at 25–30 years of cambial age. The results show that trees with 45–50 years of age and their logs up to 5 m of height may be suitable for bark and cork exploitation.

Cork Oak Young and Traumatic Periderms Show PCD Typical Chromatin Patterns but Different Chromatin-Modifying Genes Expression.

Plants are subjected to adverse conditions being outer protective tissues fundamental to their survival. Tree stems are enveloped by a periderm made of cork cells, resulting from the activity of the meristem phellogen. DNA methylation and histone modifications have important roles in the regulation of plant cell differentiation. However, studies on its involvement in cork differentiation are scarce despite periderm importance. Cork oak periderm development was used as a model to study the formation and differentiation of secondary protective tissues, and their behavior after traumatic wounding (traumatic periderm). Nuclei structural changes, dynamics of DNA methylation, and posttranslational histone modifications were assessed in young and traumatic periderms, after cork harvesting. Lenticular phellogen producing atypical non-suberized cells that disaggregate and form pores was also studied, due to high impact for cork industrial uses. Immunolocalization of active and repressive marks, transcription analysis of the corresponding genes, and correlations between gene expression and cork porosity were investigated. During young periderm development, a reduction in nuclei area along with high levels of DNA methylation occurred throughout epidermis disruption. As cork cells became more differentiated, whole nuclei progressive chromatin condensation with accumulation in the nuclear periphery and increasing DNA methylation was observed. Lenticular cells nuclei were highly fragmented with faint 5-mC labeling. Phellogen nuclei were less methylated than in cork cells, and in lenticular phellogen were even lower. No significant differences were detected in H3K4me3 and H3K18ac signals between cork cells layers, although an increase in H3K4me3 signals was found from the phellogen to cork cells. Distinct gene expression patterns in young and traumatic periderms suggest that cork differentiation might be under specific silencing regulatory pathways. Significant correlations were found between QsMET1, QsMET2, and QsSUVH4 gene expression and cork porosity. This work evidences that DNA methylation and histone modifications play a role in cork differentiation and epidermis induced tension-stress. It also provides the first insights into chromatin dynamics during cork and lenticular cells differentiation pointing to a distinct type of remodeling associated with cell death.

Different clonal responses to cypress canker disease based on transcription of suberin-related genes and bark carbohydrates’ content

Suberin metabolism plays a crucial role in the compartmentalization of the necrotic bark tissues in cypress clones resistant to bark canker caused by Seiridium cardinale. In cypress, the main mechanism of resistance to the bark canker caused by the fungal pathogen Seiridium cardinale involves the post-infectional development of a well-structured necrophylactic periderm (NP). The impermeability and effectiveness of NP against pathogens has been associated with cell wall suberization. In canker-resistant and susceptible C. sempervirens clones, the transcript accumulation of four genes involved in suberin biosynthesis (Acyl-CoA thioesterase, stearoyl-ACP-desaturase, Caffeoyl-CoA-3-O-methyltransferase 1 and Peroxidase 21) was studied in inoculated and wounded bark tissues through qPCR assay during a 3 month trial. Quantification of non-structural carbohydrates in the same targeted tissues was also performed by HPLC. In the canker-resistant clone, transcript accumulation of all four examined genes significantly increased after both inoculation or wounding more than in the susceptible clone, and the maximum difference between the two clones was observed after 30 days. The type of clone significantly affected the transcript accumulation of all the four examined genes (main effects ANOVA). The total soluble sugars content detected in the bark tissues was constitutively similar in both clones, and only slight differences in the carbon balance were detected between the two clones 90 days after inoculation or wounding. Histological observations of bark sections stained with Sudan red 90 days after inoculation, showed that in the canker-resistant clone a greater suberin deposition occurred in the NP, which resulted thicker and better structured when compared to the susceptible clone.