Proteins associated with cork formation in Quercus suber L. stem tissues

Proteomics research in forest trees: A 2012-2022 update

This review is a compilation of proteomic studies on forest tree species published in the last decade (2012-2022), mostly focused on the most investigated species, including Eucalyptus, Pinus, and Quercus. Improvements in equipment, platforms, and methods in addition to the increasing availability of genomic data have favored the biological knowledge of these species at the molecular, organismal, and community levels. Integration of proteomics with physiological, biochemical and other large-scale omics in the direction of the Systems Biology, will provide a comprehensive understanding of different biological processes, from growth and development to responses to biotic and abiotic stresses. As main issue we envisage that proteomics in long-living plants will thrive light on the plant responses and resilience to global climate change, contributing to climate mitigation strategies and molecular breeding programs. Proteomics not only will provide a molecular knowledge of the mechanisms of resilience to either biotic or abiotic stresses, but also will allow the identification on key gene products and its interaction. Proteomics research has also a translational character being applied to the characterization of the variability and biodiversity, as well as to wood and non-wood derived products, traceability, allergen and bioactive peptides identification, among others. Even thought, the full potential of proteomics is far from being fully exploited in forest tree research, with PTMs and interactomics being reserved to plant model systems. The most outstanding achievements in forest tree proteomics in the last decade as well as prospects are discussed.

Cork Development: What Lies Within

The cork layer present in all dicotyledonous plant species with radial growth is the result of the phellogen activity, a secondary meristem that produces phellem (cork) to the outside and phelloderm inwards. These three different tissues form the periderm, an efficient protective tissue working as a barrier against external factors such as environmental aggressions and pathogen attacks. The protective function offered by cork cells is mainly due to the abundance of suberin in their cell walls. Chemically, suberin is a complex aliphatic network of long chain fatty acids and alcohols with glycerol together with aromatic units. In most woody species growing in temperate climates, the first periderm is replaced by a new functional periderm upon a few years after being formed. One exception to this bark development can be found in cork oak (Quercus suber) which display a single periderm that grows continuously. Quercus suber stands by its thick cork layer development with continuous seasonal growth. Cork raw material has been exploited by man for centuries, especially in Portugal and Spain. Nowadays, its applications have widened vastly, from the most known product, stoppers, to purses or insulating materials used in so many industries, such as construction and car production. Research on how cork develops, and the effect environmental factors on cork oak trees is extremely important to maintain production of good-quality cork, and, by maintaining cork oak stands wealthy, we are preserving a very important ecosystem both by its biodiversity and its vital social and economic role in areas already showing a population declination.

Multiomics Molecular Research into the Recalcitrant and Orphan Quercus ilex Tree Species: Why, What for, and How

The holm oak (Quercus ilex L.) is the dominant tree species of the Mediterranean forest and the Spanish agrosilvopastoral ecosystem, "dehesa." It has been, since the prehistoric period, an important part of the Iberian population from a social, cultural, and religious point of view, providing an ample variety of goods and services, and forming the basis of the economy in rural areas. Currently, there is renewed interest in its use for dietary diversification and sustainable food production. It is part of cultural richness, both economically (tangible) and environmentally (intangible), and must be preserved for future generations. However, a worrisome degradation of the species and associated ecosystems is occurring, observed in an increase in tree decline and mortality, which requires urgent action. Breeding programs based on the selection of elite genotypes by molecular markers is the only plausible biotechnological approach. To this end, the authors' group started, in 2004, a research line aimed at characterizing the molecular biology of Q. ilex. It has been a challenging task due to its biological characteristics (long life cycle, allogamous, high phenotypic variability) and recalcitrant nature. The biology of this species has been characterized following the central dogma of molecular biology using the omics cascade. Molecular responses to biotic and abiotic stresses, as well as seed maturation and germination, are the two main objectives of our research. The contributions of the group to the knowledge of the species at the level of DNA-based markers, genomics, epigenomics, transcriptomics, proteomics, and metabolomics are discussed here. Moreover, data are compared with those reported for Quercus spp. All omics data generated, and the genome of Q. ilex available, will be integrated with morphological and physiological data in the systems biology direction. Thus, we will propose possible molecular markers related to resilient and productive genotypes to be used in reforestation programs. In addition, possible markers related to the nutritional value of acorn and derivate products, as well as bioactive compounds (peptides and phenolics) and allergens, will be suggested. Subsequently, the selected molecular markers will be validated by both genome-wide association and functional genomic analyses.

Molecular Research on Stress Responses in Quercus spp.: From Classical Biochemistry to Systems Biology through Omics Analysis

The genus Quercus (oak), family Fagaceae, comprises around 500 species, being one of the most important and dominant woody angiosperms in the Northern Hemisphere. Nowadays, it is threatened by environmental cues, which are either of biotic or abiotic origin. This causes tree decline, dieback, and deforestation, which can worsen in a climate change scenario. In the 21st century, biotechnology should take a pivotal role in facing this problem and proposing sustainable management and conservation strategies for forests. As a non-domesticated, long-lived species, the only plausible approach for tree breeding is exploiting the natural diversity present in this species and the selection of elite, more resilient genotypes, based on molecular markers. In this direction, it is important to investigate the molecular mechanisms of the tolerance or resistance to stresses, and the identification of genes, gene products, and metabolites related to this phenotype. This research is being performed by using classical biochemistry or the most recent omics (genomics, epigenomics, transcriptomics, proteomics, and metabolomics) approaches, which should be integrated with other physiological and morphological techniques in the Systems Biology direction. This review is focused on the current state-of-the-art of such approaches for describing and integrating the latest knowledge on biotic and abiotic stress responses in Quercus spp., with special reference to Quercus ilex, the system on which the authors have been working for the last 15 years. While biotic stress factors mainly include fungi and insects such as Phytophthora cinnamomi, Cerambyx welensii, and Operophtera brumata, abiotic stress factors include salinity, drought, waterlogging, soil pollutants, cold, heat, carbon dioxide, ozone, and ultraviolet radiation. The review is structured following the Central Dogma of Molecular Biology and the omic cascade, from DNA (genomics, epigenomics, and DNA-based markers) to metabolites (metabolomics), through mRNA (transcriptomics) and proteins (proteomics). An integrated view of the different approaches, challenges, and future directions is critically discussed.

Mass spectrometry-based forest tree metabolomics

Research in forest tree species has advanced slowly when compared with other agricultural crops and model organisms, mainly due to the long-life cycles, large genome sizes, and lack of genomic tools. Additionally, trees are complex matrices, and the presence of interferents (e.g., oleoresins and cellulose) challenges the analysis of tree tissues with mass spectrometry (MS)-based analytical platforms. In this review, advances in MS-based forest tree metabolomics are discussed. Given their economic and ecological significance, particular focus is given to Pinus, Quercus, and Eucalyptus forest tree species to better understand their metabolite responses to abiotic and biotic stresses in the current climate change scenario. Furthermore, MS-based metabolomics technologies produce large and complex datasets that require expertize to adequately manage, process, analyze, and store the data in dedicated repositories. To ensure that the full potential of forest tree metabolomics data are translated into new knowledge, these data should comply with the FAIR principles (i.e., Findable, Accessible, Interoperable, and Re-usable). It is essential that adequate standards are implemented to annotate metadata from forest tree metabolomics studies as is already required by many science and governmental agencies and some major scientific publishers. © 2019 John Wiley & Sons Ltd. Mass Spec Rev 40:126-157, 2021.

Dissecting the Seed Maturation and Germination Processes in the Non-Orthodox Quercus ilex Species Based on Protein Signatures as Revealed by 2-DE Coupled to MALDI-TOF/TOF Proteomics Strategy

Unlike orthodox species, seed recalcitrance is poorly understood, especially at the molecular level. In this regard, seed maturation and germination were studied in the non-orthodox Quercus ilex by using a proteomics strategy based on two-dimensional gel electrophoresis coupled to matrix-assisted laser desorption ionization/time of flight (2-DE-MALDI-TOF).Cotyledons and embryo/radicle were sampled at different developmental stages, including early (M1–M3), middle (M4–M7), and late (M8–M9) seed maturation, and early (G1–G3) and late (G4–G5) germination. Samples corresponding to non-germinating, inviable, seeds were also included. Protein extracts were subjected to 2-dimensional gel electrophoresis (2-DE) and changes in the protein profiles were analyzed. Identified variable proteins were grouped according to their function, being the energy, carbohydrate, lipid, and amino acid metabolisms, together with protein fate, redox homeostasis, and response to stress are the most represented groups. Beyond the visual aspect, morphometry, weight, and water content, each stage had a specific protein signature. Clear tendencies for the different protein groups throughout the maturation and germination stages were observed for, respectively, cotyledon and the embryo axis. Proteins related to metabolism, translation, legumins, proteases, proteasome, and those stress related were less abundant in non-germinating seeds, it related to the loss of viability. Cotyledons were enriched with reserve proteins and protein-degrading enzymes, while the embryo axis was enriched with proteins of cell defense and rescue, including heat-shock proteins (HSPs) and antioxidants. The peaks of enzyme proteins occurred at the middle stages (M6–M7) in cotyledons and at late ones (M8–M9) in the embryo axis. Unlike orthodox seeds, proteins associated with glycolysis, tricarboxylic acid cycle, carbohydrate, amino acid and lipid metabolism are present at high levels in the mature seed and were maintained throughout the germination stages. The lack of desiccation tolerance in Q. ilex seeds may be associated with the repression of some genes, late embryogenesis abundant proteins being one of the candidates.

Phellem Cell-Wall Components Are Discriminants of Cork Quality in Quercus suber

Cork is a renewable, non-wood high valued forest product, with relevant ecological and economic impact in the Mediterranean-type ecosystems. Currently, cork is ranked according to its commercial quality. The most valuable planks are chosen for cork stoppers production. Cork planks with adequate thickness and porosity are classified as stoppable quality cork (SQC). The chemical composition of cork is known, but the regulation of metabolic pathways responsible of cork production and composition, hence of cork quality, is largely unknown. Here, we tested the hypothesis that post-genomic events may be responsible for the development of SQC and N-SQC (non-stoppable quality cork). Here, we show that combined proteomics and targeted metabolomics (namely soluble and cell wall bound phenolics) analyzed on recently formed phellem allows discriminate cork planks of different quality. Phellem cells of SQC and N-SQC displayed different reducing capacity, with consequential impact on both enzymatic pathways (e.g., glycolysis) and other cellular functions, including cell wall assembly and suberization. Glycolysis and respiration related proteins were abundant in both cork quality groups, whereas the level of several proteins associated to mitochondrial metabolism was higher in N-SQC. The soluble and cell wall-bound phenolics in recently formed phellem clearly discriminated SQC from N-SCQ. In our study, SQC was characterized by a high incorporation of aromatic components of the phenylpropanoid pathway in the cell wall, together with a lower content of hydrolysable tannins. Here, we propose that the level of hydrolysable tannins may represent a valuable diagnostic tool for screening recently formed phellem, and used as a proxy for the quality grade of cork plank produced by each tree.

Characterization of the cork formation and production transcriptome in Quercus cerris × suber hybrids

Cork oak is the main cork-producing species worldwide, and plays a significant economic, ecological and social role in the Mediterranean countries, in particular in Portugal and Spain. The ability to produce cork is limited to a few species, hence it must involve specific regulation mechanisms that are unique to these species. However, to date, these mechanisms remain largely understudied, especially with approaches involving the use of high-throughput sequencing technology. In this study, the transcriptome of cork-producing and non-cork-producing Quercus cerris × suber hybrids was analyzed in order to elucidate the differences between the two groups of trees displaying contrasting phenotypes for cork production. The results revealed the presence of a significant number of genes exclusively associated with cork production, in the trees that developed cork. Moreover, several gene ontology subcategories, such as cell wall biogenesis, lipid metabolic processes, metal ion binding and apoplast/cell wall, were only detected in the trees with cork production. These results indicate the existence, at the transcriptome level, of mechanisms that seem to be unique and necessary for cork production, which is an advancement in our knowledge regarding the genetic regulation behind cork formation and production.

Transcriptional profiling of cork oak phellogenic cells isolated by laser microdissection

The phenylpropanoid pathway impacts the cork quality development. In cork of bad quality, the flavonoid route is favored, whereas in good quality, cork lignin and suberin production prevails. Cork oaks develop a thick cork tissue as a protective shield that results of the continuous activity of a secondary meristem, the cork cambium, or phellogen. Most studies applied to developmental processes do not consider the cell types from which the samples were extracted. Here, laser microdissection (LM) coupled with transcript profiling using RNA sequencing (454 pyrosequencing) was applied to phellogen cells of trees producing low- and good quality cork. Functional annotation and functional enrichment analyses showed that stress-related genes are enriched in samples extracted from trees producing good quality cork (GQC). This process is under tight transcriptional (transcription factors, kinases) regulation and also hormonal control involving ABA, ethylene, and auxins. The phellogen cells collected from trees producing bad quality cork (BQC) show a consistent up-regulation of genes belonging to the flavonoid pathway as a response to stress. They also display a different modulation of cell wall genes resulting into a thinner cork layer, i.e., less meristematic activity. Based on the analysis of the phenylpropanoid pathway regulating genes, in GQC, the synthesis of lignin and suberin is promoted, whereas in BQC, the same pathway favors the biosynthesis of free phenolic compounds. This study provided new insights of how cell-specific gene expression can determine tissue and organ morphology and physiology and identified robust candidate genes that can be used in breeding programs aiming at improving cork quality.

A comparative transcriptomic approach to understanding the formation of cork

The transcriptome comparison of two oak species reveals possible candidates accounting for the exceptionally thick and pure cork oak phellem, such as those involved in secondary metabolism and phellogen activity. Cork oak, Quercus suber, differs from other Mediterranean oaks such as holm oak (Quercus ilex) by the thickness and organization of the external bark. While holm oak outer bark contains sequential periderms interspersed with dead secondary phloem (rhytidome), the cork oak outer bark only contains thick layers of phellem (cork rings) that accumulate until reaching a thickness that allows industrial uses. Here we compare the cork oak outer bark transcriptome with that of holm oak. Both transcriptomes present similitudes in their complexity, but whereas cork oak external bark is enriched with upregulated genes related to suberin, which is the main polymer responsible for the protective function of periderm, the upregulated categories of holm oak are enriched in abiotic stress and chromatin assembly. Concomitantly with the upregulation of suberin-related genes, there is also induction of regulatory and meristematic genes, whose predicted activities agree with the increased number of phellem layers found in the cork oak sample. Further transcript profiling among different cork oak tissues and conditions suggests that cork and wood share many regulatory mechanisms, probably reflecting similar ontogeny. Moreover, the analysis of transcripts accumulation during the cork growth season showed that most regulatory genes are upregulated early in the season when the cork cambium becomes active. Altogether our work provides the first transcriptome comparison between cork oak and holm oak outer bark, which unveils new regulatory candidate genes of phellem development.

Engineering the expression level of cytosolic nucleoside diphosphate kinase in transgenic Solanum tuberosum roots alters growth, respiration and carbon metabolism

Nucleoside diphosphate kinase (NDPK) is a ubiquitous enzyme that catalyzes the transfer of the γ-phosphate from a donor nucleoside triphosphate to an acceptor nucleoside diphosphate. In this study we used a targeted metabolomic approach and measurement of physiological parameters to report the effects of the genetic manipulation of cytosolic NDPK (NDPK1) expression on physiology and carbon metabolism in potato (Solanum tuberosum) roots. Sense and antisense NDPK1 constructs were introduced in potato using Agrobacterium rhizogenes to generate a population of root clones displaying a 40-fold difference in NDPK activity. Root growth, O₂ uptake, flux of carbon between sucrose and CO₂ , levels of reactive oxygen species and some tricarboxylic acid cycle intermediates were positively correlated with levels of NDPK1 expression. In addition, NDPK1 levels positively affected UDP-glucose and cellulose contents. The activation state of ADP-glucose pyrophosphorylase, a key enzyme in starch synthesis, was higher in antisense roots than in roots overexpressing NDPK1. Further analyses demonstrated that ADP-glucose pyrophosphorylase was more oxidized, and therefore less active, in sense clones than antisense clones. Consequently, antisense NDPK1 roots accumulated more starch and the starch to cellulose ratio was negatively affected by the level of NDPK1. These data support the idea that modulation of NDPK1 affects the distribution of carbon between starch and cellulose biosynthetic pathways.

The role of nitrogen in leaf senescence of summer maize and analysis of underlying mechanisms using comparative proteomics

Leaf senescence is associated with fundamental changes on the level of the proteome and it can be modulated by nitrogen. To determine the precise regulatory mechanisms underlying these effects, we conducted a comparative proteomics study using 2-dimensional gel electrophoresis and MALDI-TOF/TOF MS. Based on our study of the maize leaf proteome, leaf senescence induces complex responses including the degradation of 32 senescence-associated proteins that are involved in many biological processes, especially energy, metabolism and cell rescue, defense and virulence pathways. Although similar conclusions have been highlighted in other crops, this study filled the knowledge gap in maize leaf senescence. Moreover, we discovered, for the first time, 29 "nitrogen-regulated senescence proteins" had significant (P≤0.05) interaction term for nitrogen×stage. Although further study of nitrogen-related senescence proteins, such as 30S ribosomal protein, will be required to fully elucidate their complex functions, the surprising results in our study provide a new vision to research the relationship between nitrogen and senescence.

Comparison of good- and bad-quality cork: application of high-throughput sequencing of phellogenic tissue

Cork is one of the most valuable non-wood forest products and plays an important role in Mediterranean economies. The production of high-quality cork is dependent on both genome and environment, posing constraints on the industry because an ever-growing amount of bad-quality cork (BQC) development has been observed. In order to identify genes responsible for production of cork of superior quality we performed a comparative analysis using the 454 pyrosequencing approach on phellogenic tissue of good- and bad-quality samples. The transcriptional profiling showed a high number of genes differentially expressed (8.48%) from which 78.8% displayed annotation. Genes more highly represented in BQC are involved in DNA synthesis, RNA processing, proteolysis, and transcription factors related to the abiotic stress response. Putative stomatal/lenticular-associated genes which may be responsible for the disadvantageous higher number of lenticular channels in BQC are also more highly represented. BQC also showed an elevated content of free phenolics. On the other hand, good-quality cork (GQC) can be distinguished by highly expressed genes encoding heat-shock proteins. Together the results provide valuable new information about the molecular events leading to cork formation and provide putative biomarkers associated with cork quality that can be useful in breeding programmes.

Clues to the functions of plant NDPK isoforms

This review describes the five nucleoside diphosphate kinase (NDPK) genes found in both model plants Arabidopsis thaliana (thale cress) and Oryza sativa L. (rice). Phylogenetic and sequence analyses of these genes allow the definition of four types of NDPK isoforms with different predicted subcellular localization. These predictions are supported by experimental evidence for most NDPK types. Data mining also provides evidence for the existence of a novel NDPK type putatively localized in the endoplasmic reticulum. Phylogenic analyses indicate that plant types I, II, and III belong to the previously identified Nme group I whereas type IV belongs to Nme group II. Additional analysis of the literature offers clues supporting the idea that the various plant NDPK types have different functions. Hence, cytosolic type I NDPKs are involved in metabolism, growth, and stress responses. Type II NDPKs are localized in the chloroplast and mainly involved in photosynthetic development and oxidative stress management. Type III NDPKs have dual targeting to the mitochondria and the chloroplast and are principally involved in energy metabolism. The subcellular localization and precise function of the novel type IV NDPKs, however, will require further investigations.

Effect of greenhouse conditions on the leaf apoplastic proteome of Coffea arabica plants

This work describes the coffee leaf apoplastic proteome and its modulation by the greenhouse conditions. The apoplastic fluid (APF) was obtained by leaf vacuum infiltration, and the recovered proteins were separated by 2-DE and subsequently identified by matrix assisted laser desorption/ionization time of flight-mass spectrometry, followed by homology search in EST coffee databases. Prediction tools revealed that the majority of the 195 identified proteins are involved in cell wall metabolism and in stress/defense responses. Although most of the proteins follow the classical secretory mechanism, a low percentage of them seem to result from unconventional secretion (leaderless secreted proteins). Principal components analysis revealed that the APF samples formed two distinct groups, with the temperature amplitude mostly contributing for this separation (higher or lower than 10°C, respectively). Sixty one polypeptide spots allowed defining these two groups and 28 proteins were identified, belonging to carbohydrate metabolism, cell wall modification and proteolysis. Interestingly stress/defense proteins appeared as more abundant in Group I which is associated with a higher temperature amplitude. It seems that the proteins in the coffee leaf APF might be implicated in structural modifications in the extracellular space that are crucial for plant development/adaptation to the conditions of the prevailing environment.

BIOLOGICAL SIGNIFICANCE

This is the first detailed proteomic study of the coffee leaf apoplastic fluid (APF) and of its modulation by the greenhouse conditions. The comprehensive overview of the most abundant proteins present in the extra-cellular compartment is particularly important for the understanding of coffee responses to abiotic/biotic stress. This article is part of a Special Issue entitled: Environmental and structural proteomics.

Protein extraction from plant tissues for 2DE and its application in proteomic analysis

Plant tissues contain large amounts of secondary compounds that significantly interfere with protein extraction and 2DE analysis. Thus, sample preparation is a crucial step prior to 2DE in plant proteomics. This tutorial highlights the guidelines that need to be followed to perform an adequate total protein extraction before 2DE in plant proteomics. We briefly describe the history, development, and feature of major sample preparation methods for the 2DE analysis of plant tissues, that is, trichloroacetic acid/acetone precipitation and phenol extraction. We introduce the interfering compounds in plant tissues and the general guidelines for tissue disruption, protein precipitation and resolubilization. We describe in details the advantages, limitations, and application of the trichloroacetic acid/acetone precipitation and phenol extraction methods to enable the readers to select the appropriate method for a specific species, tissue, or cell type. The current applications of the sample preparation methods in plant proteomics in the literature are analyzed. A comparative proteomic analysis between male and female plants of Pistacia chinensis is used as an example to represent the sample preparation methodology in 2DE-based proteomics. Finally, the current limitations and future development of these sample preparation methods are discussed. This Tutorial is part of the International Proteomics Tutorial Programme (IPTP17).

A possible approach for gel-based proteomic studies in recalcitrant woody plants

Woody plants are particularly difficult to investigate due to high phenolic, resin, and tannin contents and laborious sample preparation. In particular, protein isolation from woody plants for two-dimensional gel electrophoresis (2-DE) is challenging as secondary metabolites negatively interfere with protein extraction and separation. In this study, three protein extraction protocols, using TCA, phenol and ethanol as precipitation or extraction agents, were tested in order to select the more efficient for woody recalcitrant plant gel-based proteomics. Grapevine leaves, pine needles and cork oak ectomycorrhizal roots were used to represent woody plant species and tissues. The phenol protocol produced higher quality 2-DE gels, with increased number of resolved spots, better spot focusing and representation of all molecular mass and isoelectric point ranges tested. In order to test the compatibility of the phenol extracted proteomes with protein identification several spots were excised from the phenol gels and analyzed by mass spectrometry (MALDI-TOF/TOF). Regardless the incomplete genome/protein databases for the plant species under analysis, 49 proteins were identified by Peptide Mass Fingerprint (PMF). Proteomic data have been deposited to the ProteomeXchange with identifier PXD000224. Our results demonstrate the complexity of protein extraction from woody plant tissues and the suitability of the phenol protocol for obtaining high quality protein extracts for efficient 2-DE separation and downstream applications such as protein identification by mass spectrometry.

Molecular characterization of Quercus suber MYB1, a transcription factor up-regulated in cork tissues

The molecular processes associated with cork development in Quercus suber L. are poorly understood. A previous molecular approach identified a list of genes potentially important for cork formation and differentiation, providing a new basis for further molecular studies. This report is the first molecular characterization of one of these candidate genes, QsMYB1, coding for an R2R3-MYB transcription factor. The R2R3-MYB gene sub-family has been described as being involved in the phenylpropanoid and lignin pathways, both involved in cork biosynthesis. The results showed that the expression of QsMYB1 is putatively mediated by an alternative splicing (AS) mechanism that originates two different transcripts (QsMYB1.1 and QsMYB1.2), differing only in the 5'-untranslated region, due to retention of the first intron in one of the variants. Moreover, within the retained intron, a simple sequence repeat (SSR) was identified. The upstream regulatory region of QsMYB1 was extended by a genome walking approach, which allowed the identification of the putative gene promoter region. The relative expression pattern of QsMYB1 transcripts determined by reverse transcription quantitative polymerase chain reaction (RT-qPCR) revealed that both transcripts were up-regulated in cork tissues; the detected expression was several times higher in newly formed cork harvested from trees producing virgin, second or reproduction cork when compared with wood. Moreover, the expression analysis of QsMYB1 in several Q. suber organs showed very low expression in young branches and roots, whereas in leaves, immature acorns or male flowers, no expression was detected. These preliminary results suggest that QsMYB1 may be related to secondary growth and, in particular, with the cork biosynthesis process with a possible alternative splicing mechanism associated with its regulatory function.