Tension Wood Formation Research Articles

PagKNAT2/6b regulates tension wood formation and gravitropism by targeting cytokinin metabolism.

Tension wood is a specialized xylem tissue associated with gravitropism in angiosperm trees. However, few regulators of tension wood formation have been identified. The molecular mechanisms underpinning tension wood formation remain elusive. Here, we report that a Populus KNOTTED-like homeobox gene, PagKNAT2/6b, is involved in tension wood formation and gravity response. Transgenic poplar plants overexpressing PagKNAT2/6b displayed more sensitive gravitropism than controls, as indicated by increased stem curvature. Microscopic examination revealed greater abundance of fibre cells with a gelatinous cell wall layer (G-layer) and asymmetric growth of secondary xylem in PagKNAT2/6b overexpression lines. Conversely, PagKNAT2/6b dominant repression plants exhibited decreased tension wood formation and reduced response to gravity stimulation. Moreover, sensitivity to gravity stimulation showed a negative relationship with development stage. Expression of genes related to growth and senescence was affected in PagKNAT2/6b transgenic plants. More importantly, transcription activation and electrophoretic mobility shift assays suggested that PagKNAT2/6b promotes the expression of cytokinin metabolism genes. Consistently, cytokinin content was increased in PagKNAT2/6b overexpression plants. Therefore, PagKNAT2/6b is involved in gravitropism and tension wood formation, likely via modulation of cytokinin metabolism.

A COBRA family protein, PtrCOB3, contributes to gelatinous layer formation of tension wood fibers in poplar.

Angiosperm trees usually develop tension wood (TW) in response to gravitational stimulation. TW comprises abundant gelatinous (G-) fibers with thick G-layers primarily composed of crystalline cellulose. Understanding the pivotal factors governing G-layer formation in TW fiber remains elusive. This study elucidates the role of a Populus trichocarpa COBRA family protein, PtrCOB3, in the G-layer formation of TW fibers. PtrCOB3 expression was upregulated, and its promoter activity was enhanced during TW formation. Comparative analysis with wild-type trees revealed that ptrcob3 mutants, mediated by Cas9/gRNA gene editing, were incapable of producing G-layers within TW fibers and showed severely impaired stem lift. Fluorescence immunolabeling data revealed a dearth of crystalline cellulose in the tertiary cell wall (TCW) of ptrcob3 TW fibers. The role of PtrCOB3 in G-layer formation is contingent upon its native promoter, as evidenced by the comparative phenotypic assessments of pCOB11::PtrCOB3, pCOB3::PtrCOB3, and pCOB3::PtrCOB11 transgenic lines in the ptrcob3 background. Overexpression of PtrCOB3 under the control of its native promoter expedited G-layer formation within TW fibers. We further identified 3 transcription factors that bind to the PtrCOB3 promoter and positively regulate its transcriptional levels. Alongside the primary TCW synthesis genes, these findings enable the construction of a 2-layer transcriptional regulatory network for the G-layer formation of TW fibers. Overall, this study uncovers mechanistic insight into TW formation, whereby a specific COB protein executes the deposition of cellulose, and consequently, G-layer formation within TW fibers.

Analysis of genes related to xylem cell wall development based on transcriptomics in Populus alba ‘Berolinensis’ tension wood

Populus alba ‘Berolinensis’ is a fast-growing, high-yielding species with strong biotic and abiotic stress resistance, and widely planted for timber, shelter belts and aesthetic purposes. In this study, molecular development is explored and the important genes regulating xylem formation in P. alba ‘Berolinensis’ under artificial bending treatments was identified. Anatomical investigation indicated that tension wood (TW) was characterized by eccentric growth of xylem and was enriched in cellulose; the degree of lignification was lower than for normal wood (NW) and opposite wood (OW). RNA-Seq-based transcriptome analysis was performed using developing xylem from three wood types (TW, OW and NW). A large number of differentially expressed genes (DEGs) were screened and 4889 counted. In GO and KEGG enrichment results, genes involved in plant hormone signal transduction, phenylpropanoid biosynthesis, and cell wall and secondary cell wall biogenesis play major roles in xylem development under artificial bending. Eight expansin (PalEXP) genes were identified from the RNA-seq data; four were differentially expressed during tension wood formation. Phylogenetic analysis indicated that PalEXLB1 belongs to the EXPB subfamily and that the other PalEXPs are members of the EXPA subfamily. A transcriptional regulatory network construction showed 10 transcription factors located in the first and second layers upstream of EXP, including WRKY, ERF and bHLH. RT‒qPCR analysis in leaves, stems and roots combined with transcriptome analysis suggests that PalEXPA2, PalEXPA4 and PalEXPA15 play significant regulatory roles in cell wall formation during tension wood development. The candidate genes involved in xylem cell wall development during tension wood formation marks an important step toward identifying the molecular regulatory mechanism of xylem development and wood property improvement in P. alba ‘Berolinensis’.

Landslide development model based on tree-ring data and quantification of the magnitude of landslide movements

Analysis of landslide events by studying anomalies in tree-ring series of disturbed trees provides unique data on past landslide behaviour. However, a comprehensive spatio-temporal model of landslide evolution using dendrogeomorphic data has not yet been constructed. In terms of determining landslide hazard, one of the key issues, besides the frequency of movements, is their magnitude. Thus, this study is aimed at constructing a model of landslide area development including quantification of landslide displacements. Moreover, not only standard macroscopic growth disturbance but also quantitative anatomical parameters of tree rings were used as a basis for these objectives. The research was carried out on a landslide of the Váh river bank (Slovakia) using data from 32 disturbed black locust (Robinia pseudoacacia L.) individuals. Anatomical analysis revealed a reduction in the vessel lumen area in response to landslide movements. The response was associated with tension wood formation or damage to the tree root system. The reconstructed chronology of landslide movements revealed the main phase of landslide in 2017 and its subsequent evolution. Based on the chronological information and the morphology of the landslide body, a spatio-temporal model of the landslide evolution from the initial slope failure to the present was constructed. The model showed the interrelationships between vertical displacement of the main block, compression and tension deformations within the landslide body, and lateral erosion of the landslide toe by the river. Quantification of the magnitude of landslide displacements was realized from exposed roots in tension cracks but also from the ruptured tree trunk. The limitations and advantages of both approaches are discussed.

Flexure wood formation via growth reprogramming in hybrid aspen involves jasmonates and polyamines and transcriptional changes resembling tension wood development.

Stem bending in trees induces flexure wood but its properties and development are poorly understood. Here, we investigated the effects of low-intensity multidirectional stem flexing on growth and wood properties of hybrid aspen, and on its transcriptomic and hormonal responses. Glasshouse-grown trees were either kept stationary or subjected to several daily shakes for 5 wk, after which the transcriptomes and hormones were analyzed in the cambial region and developing wood tissues, and the wood properties were analyzed by physical, chemical and microscopy techniques. Shaking increased primary and secondary growth and altered wood differentiation by stimulating gelatinous-fiber formation, reducing secondary wall thickness, changing matrix polysaccharides and increasing cellulose, G- and H-lignin contents, cell wall porosity and saccharification yields. Wood-forming tissues exhibited elevated jasmonate, polyamine, ethylene and brassinosteroids and reduced abscisic acid and gibberellin signaling. Transcriptional responses resembled those during tension wood formation but not opposite wood formation and revealed several thigmomorphogenesis-related genes as well as novel gene networks including FLA and XTH genes encoding plasma membrane-bound proteins. Low-intensity stem flexing stimulates growth and induces wood having improved biorefinery properties through molecular and hormonal pathways similar to thigmomorphogenesis in herbaceous plants and largely overlapping with the tension wood program of hardwoods.

Recent genome resequencing paraded COBRA-Like gene family roles in abiotic stress and wood formation in Poplar.

A cell wall determines the mechanical properties of a cell, serves as a barrier against plant stresses, and allows cell division and growth processes. The COBRA-Like (COBL) gene family encodes a putative glycosylphosphatidylinositol (GPI)-anchored protein that controls cellulose deposition and cell progression in plants by contributing to the microfibril orientation of a cell wall. Despite being studied in different plant species, there is a dearth of the comprehensive global analysis of COBL genes in poplar. Poplar is employed as a model woody plant to study abiotic stresses and biomass production in tree research. Improved genome resequencing has enabled the comprehensive exploration of the evolution and functional capacities of PtrCOBLs (Poplar COBRA-Like genes) in poplar. Phylogeny analysis has discerned and classified PtrCOBLs into two groups resembling the Arabidopsis COBL family, and group I genes possess longer proteins but have fewer exons than group II. Analysis of gene structure and motifs revealed PtrCOBLs maintained a rather stable motif and exon-intron pattern across members of the same group. Synteny and collinearity analyses exhibited that the evolution of the COBL gene family was heavily influenced by gene duplication events. PtrCOBL genes have undergone both segmental duplication and tandem duplication, followed by purifying selection. Promotor analysis flaunted various phytohormone-, growth- and stress-related cis-elements (e.g., MYB, ABA, MeJA, SA, AuxR, and ATBP1). Likewise, 29 Ptr-miRNAs of 20 families were found targeting 11 PtrCOBL genes. PtrCOBLs were found localized at the plasma membrane and extracellular matrix, while gene ontology analysis showed their involvement in plant development, plant growth, stress response, cellulose biosynthesis, and cell wall biogenesis. RNA-seq datasets depicted the bulk of PtrCOBL genes expression being found in plant stem tissues and leaves, rendering mechanical strength and rejoinders to environmental cues. PtrCOBL2, 3, 10, and 11 manifested the highest expression in vasculature and abiotic stress, and resemblant expression trends were upheld by qRT-PCR. Co-expression network analysis identified PtrCOBL2 and PtrCOBL3 as hub genes across all abiotic stresses and wood developing tissues. The current study reports regulating roles of PtrCOBLs in xylem differentiating tissues, tension wood formation, and abiotic stress latency that lay the groundwork for future functional studies of the PtrCOBL genes in poplar breeding.

Structure of cellulose in birch phloem fibres in tension wood: an X-ray nanodiffraction study

BackgroundTo gain a better understanding of bark layer structure and function, especially of the phloem fibres and their contribution to the posture control of trees, it is important to map the structural properties of these cells. The role of bark can also be linked to the reaction wood formation and properties which are essential when it comes to studying the questions related to tree growth. To offer new insights into the role of bark in the postural control of trees, we studied the micro- and nanoscale structures of the phloem and its nearest layers. This study is the first time, in which phloem fibres in trees have been extensively examined using X-ray diffraction (XRD).We determined the orientation of cellulose microfibrils in phloem fibres of Silver birch saplings by using scanning synchrotron nanodiffraction. The samples consisted of phloem fibres extracted from tension, opposite and normal wood (TW, OW, NW).ResultsUsing scanning XRD, we were able to obtain new information about the mean microfibril angle (MFA) in cellulose microfibrils in phloem fibres connected to reaction wood. A slight but consistent difference was detected in the average MFA values of phloem fibres between the TW and OW sides of the stem. Using scanning XRD, different contrast agents (intensity of the main cellulose reflection or calcium oxalate reflection, mean MFA value) were used to produce 2D images with 200 nm spatial resolution.ConclusionsBased on our results, the tension wood formation in the stem might be related to the structure and properties of phloem fibres. Thus, our results suggest that the nanostructure of phloem fibres is involved in the postural control of trees containing tension and opposite wood.

Distribution of Plant Hormones and Their Precursors in Cambial Region Tissues of Quercus myrsinifolia and Castanopsis cuspidata var.sieboldii after Bending Stems or Applying Ethylene precursor

The role of plant hormones in tension wood (TW) formation has been studied but is still unclear. IAA, ABA, ACC, tZ, tZR, iP, and iPR in cambial region tissues were identified and quantified by liquid chromatography/mass spectrometry (LC/MS). We examined the distribution of plant hormones and their precursors in the stems of Quercus myrsinifolia Blume and Castanopsis cuspidata var.sieboldii Nakai after bending the stems or applying an ethylene precursor (ACC). After 3 weeks of bending, though not after 1 week of bending, the auxin (IAA) and abscisic acid (ABA) amounts were larger on the TW side than on the opposite wood (OW) side and in upright trees. After 2 weeks of bending, the peak concentrations of IAA in cambium on the TW side were obviously higher than those on the OW side. After 1 week of bending, the ACC amounts on both sides were larger than in upright trees, but after 3 weeks of bending, they were smaller than in upright trees. Applied ACC did not enhance TW formation but induced axical parenchyma and phloem formation in C. cuspidata var.sieboldii. These results indicated that the distribution patterns of IAA and ABA might have important roles in TW formation in these two species. The role of ACC might be limited in the early stages of TW formation.

Tissue Metabolic Responses to Artificial Bending and Gravitation Stimuli in Betula platyphylla

Betula platyphylla Suk (Asian white birch) is an economically important tree species in the paper-pulping and biofuel industries. To investigate the mechanism of wood formation at the metabolic level, we evaluated metabolic responses associated with tension-wood formation. Four-year-old trees were subjected to artificial bending treatment for 6 weeks. The xylem growth rate of tension wood (TW) was significantly faster than that of opposite wood (OW), and it exhibited a higher cellulose content. Metabolomics analysis was performed on metabolites of TW, OW and normal wood (NW), and 183 metabolites were identified, of which levels of 142 were altered between groups. Metabolites related to fatty-acid and amino-acid metabolism, the glycolytic pathway, and the metabolism of fructose, mannose and starch sucrose were abundant in TW. Glucose 1-phosphoric acid, fructose and mannose associated with tension-wood development were elevated. Levels of xylitol and ribosol (related to the conversion of glucose), coniferol (the main monomer of lignin) and shikimic acid (an intermediate in lignin synthesis) were decreased in TW. These metabolites are likely involved in xylem development.

Anatomical growth response of Fagus sylvatica L. to landslide movements

Determining the age of landslide events is crucial for determining landslide risk, triggers, and also for predicting future landslide occurrence. Currently, the most accurate method for dating historical landslide events is dendrogeomorphic analysis. Unfortunately, the standard use of macroscopic growth responses of damaged trees for dating landslide activity suffers from many shortcomings. Thus, the aim of this study is to analyze in detail the growth response of trees to landslide movements at the anatomical level, a completely groundbreaking methodological approach. Ten specimens of European beech (Fagus sylvatica L.) were analyzed at two sampling heights, growing in two morphologically contrasting zones of the landslide area. Detailed anatomical analysis was focused on changes in morphometric parameters of the vessels and in the number of radial rays. The period (2008–2012) with the occurrence of the largest landslide movement (2010) recorded by long-term monitoring was analyzed. The results obtained revealed different anatomical responses in trees growing in different morphological zones of landslide. The tree responses on the ridge corresponded to the manifestations of tension wood formation, which corresponded to the stem tilting due to the landslide block movement. In the case of the trees in the trenches, root damage due to the subsidence of the landslide block blocked the flux of phytohormones, and their accumulation caused a significant reduction in the parameters of vessels and an increase in the number of rays. The study also includes recommendations in the future application of anatomical analyses in landslide research resulting from the obtained results. Thus, the obtained findings will improve the acquisition of chronological data for the purpose of landslide risk assessment.

The tree-ring anatomy of Robinia pseudoacacia L. As a data source for dendrogeomorphic reconstruction of past landslide movements in the landslide hot-spot of central Europe

The chronology of past landslide movements is a key source of information for effective landslide hazard determination. Dendrogeomorphological methods are currently an effective tool for obtaining chronological data but still encounter limitations in extracting landslide signals from yearly series. These limitations can be reduced by introducing anatomical analyses of the yearly series. Black locust (Robinia pseudoacacia L.), a widespread tree species occupying landslides on river banks, has been surprisingly rare in dendrogeomorphology. Thus, this study focused on the effectiveness of using both standard macroscopic signals (tree-ring eccentricity) and anatomical growth responses of this species in a dendrogeomorphic analysis of landslide movements at one of the landslide hot spots in Central Europe (the Váh River bank). Analysis of the eccentricity of tree rings from 67 individuals of R. pseudoacacia allowed us to reconstruct 13 landslide events over the last 49 years. From an anatomical point of view, a strong association was found between a significant reduction in vessel lumen area and the eccentricity of the tree rings and the tilting of the tree stems. A possible cause of the anatomical response is a combination of root damage from subsurface landslide movements and occasional tension wood formation following tree tilting. The constructed chronology confirmed the known years of landslide activity and generally complemented the known chronology. One of the results of the study is the implication for effective evaluation of the spatial extent of landslide activity, considering tree-ring-based magnitude-frequency relationships. The results of this study will thus allow further extension of the use of dendrogeomorphological methods both methodologically and biogeographically.

Chemical variations in tension wood of poplar tree induced by intermittent bending, fertilizer and hormone treatments

Tree growth is influenced by various environmental factors that lead to anatomical, physical and chemical changes in their wood. Reaction wood is one of the tree's reactions that make many restrictions in wood usages. Reaction wood in broadleaf is called tension wood. This study was aimed to stimulate the formation of tension wood in two-year-old seedlings of Populus alba by using intermittent bending, nitrogen fertilization and gibberellin hormone. The application of different treatments increased the content of cellulose compared to the control sample. Meanwhile, the bent specimens had more increase while the straight specimens had no significant difference in the statistical grouping. The content of lignin decreased in all treatments compared to the control sample. The cellulose/lignin ratios obtained from ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared) analysis of wood sawdust and chemical composition measurements were almost close to each other and were higher in the treated samples than in the control. The degree of crystallinity obtained from XRD (X-ray Diffraction) measurements showed that all samples under intermittent bending had a significantly higher degree of crystallinity than the control sample, while this increase was not significant in all straight samples compared to the control sample. In general, it can be concluded that intermittent bending treatment had a greater effect on the stimulation and changes of chemical properties of tension wood in poplar and the application of nitrogen fertilization and gibberellin hormone increased this effect. The formation of gelatinous layer in the innermost part of the intermittent bent seedlings fiber cell wall was visible in light microscope images.

Variations in tension wood characteristics of Populus alba under alternate bending, nitrogen fertilization, and gibberellin treatments

Summary Reaction wood formation (tension wood) in trees such as poplar is a response to stress and environmental factors. Tension wood is a rich source of cellulose that can be used for products including paper or biofuels and is thus a target product in forestry. This study aimed to evaluate the formation of tension wood in two-year-old saplings of Populus alba by using alternate bending, nitrogen fertilization, and gibberellin hormone. Saplings were bent alternately in one or another direction every month during the growing season, fertilized twice at the beginning and in the middle of the growing season, and treated with gibberellin early in the growing season. The physical and anatomical characteristics of the wood were studied after the end of the growing season. Evaluation of transverse sections of specimens stained with safranin/Astra-blue showed that, compared with straight saplings, alternate bending saplings had a wider tension wood area in the growth ring and clear formation of a gelatinous layer. The wood of alternate bending saplings with nitrogen fertilization and gibberellin hormone had a higher wood density, greater longitudinal shrinkage, and less radial and tangential shrinkage than saplings with other treatments. Moreover, the alternate bending saplings treated with nitrogen fertilization and gibberellin hormone had tension wood with the largest vessels, the lowest vessel density, and the smallest total vessel lumen area than saplings with other treatments. Wood fibers of treated saplings also had the thickest wall with the smallest fiber and lumen diameters. Overall, the bending treatment with the addition of nitrogen fertilization and gibberellin hormone was the most effective for the stimulation of tension wood formation in terms of volume and intensity.

Ethylene regulates miRNA-mediated lignin biosynthesis and leaf serration in Arabidopsis thaliana

microRNAs (miRNAs) regulate target gene expression by pairing to target mRNAs, leading to mRNA degradation or translation inhibition. Out of several miRNAs in Arabidopsis, miR397b and miR857 regulate secondary growth by modulating lignin polymerization and deposition in secondary xylem cells by targeting laccases. Interestingly, the phytohormone ethylene is also suggested to have a role in lignin biosynthesis in tension wood formation. Despite this information, it is not known whether ethylene has any role in controlling secondary growth via miRNAs-mediated pathways. In this study, we elucidate that ethylene acts upstream to the miR397b/miR857-laccases module and negatively regulates lignin biosynthesis by directly activating the expression of both the miRNAs. The binding of EIN3 to the promoter of miR397b is further validated by yeast one-hybrid assay. In addition to its role in lignification, ethylene also regulates leaf serration by directly regulating the expression of NAC transcription factors, like CUP-SHAPED COTYLEDON2 (CUC2) and CUC3. Together, our study suggests a novel mechanism involving ethylene and miRNAs in lignin biosynthesis and leaf serration in Arabidopsis thaliana.

Transcriptomic, Proteomic, and Metabolic Profiles of Catalpa bungei Tension Wood Reveal New Insight Into Lignin Biosynthesis Involving Transcription Factor Regulation.

Lignin is a complex polymer in plant cell walls whose proportion is second only to that of cellulose and plays an important role in the mechanical properties of wood and stress resistance of plants. Here, we induced tension wood (TW) formation in Catalpa bungei by artificial bending and analyzed the lignin metabolism of the TW. LC-MS analysis showed that a significantly higher content of coniferyl aldehyde was observed in the TW cell wall than in the opposite wood (OW) and normal wood (NW) cell walls. TW had significantly lower contents of coniferyl alcohol than OW and NW. Raman spectroscopy results indicated that TW had lower total lignin than OW and NW. The transcription and translation levels of most of the differentially expressed genes (DEGs) involved in lignin monomer biosynthesis indicated upregulation in TW/OW and TW/NW. We found no significant difference in the transcription levels of three collision gases (CADs) between TW and OW or between NW, but their translation levels were significantly downregulated in TW, suggesting post-transcriptional control for CAD. We predicted and analyzed transcription factors that could target DEGs involved in lignin monomer biosynthesis in TW. Based on the analysis of the relationships of targeting and coexpression, we found that NAC (evm.model.group1.695) could potentially target 4CLs and CCoAOMT, that HD-Zip (evm.model.group7.1157) had potential targeting relationships with CCoAOMT, F5H, and CCR, and that their expression levels were significantly positive. It is speculated that the upregulation of NAC and HD-ZIP transcription factors activates the expression of downstream target genes, which leads to a significant increase in coniferyl aldehyde in TW. However, the decrease in total lignin in TW may be caused by the significant downregulation of CAD translation and the significant decrease in precursors (coniferyl alcohol). Whether the expression of CAD genes is regulated by post-transcriptional control and affects TW lignin metabolism needs further study.

A PtrLBD39-mediated transcriptional network regulates tension wood formation in Populus trichocarpa

Tension wood (TW) is a specialized xylem tissue formed in angiosperm trees under gravitational stimulus or mechanical stresses (e.g., bending). The genetic regulation that underlies this important mechanism remains poorly understood. Here, we used laser capture microdissection of stem xylem cells coupled with full transcriptome RNA-sequencing to analyze TW formation in Populus trichocarpa. After tree bending, PtrLBD39 was the most significantly induced transcription factor gene; it has a phylogenetically paired homolog, PtrLBD22. CRISPR-based knockout of PtrLBD39/22 severely inhibited TW formation, reducing cellulose and increasing lignin content. Transcriptomic analyses of CRISPR-based PtrLBD39/22 double mutants showed that these two genes regulate a set of TW-related genes. Chromatin immunoprecipitation sequencing (ChIP-seq) was used to identify direct targets of PtrLBD39. We integrated transcriptomic analyses and ChIP-seq assays to construct a transcriptional regulatory network (TRN) mediated by PtrLBD39. In this TRN, PtrLBD39 directly regulates 26 novel TW-responsive transcription factor genes. Our work suggests that PtrLBD39 and PtrLBD22 specifically control TW formation by mediating a TW-specific TRN in Populus.

The potential of tension wood for the detection of landslide signals in the tree ring series of Fagus sylvatica L.: The extension of dendrogeomorphic tools for landslide analysis

The knowledge of past landslide movement chronology is crucial for estimating future landslide development or for detailed analysis of triggers. A very precise approach to landslide history detection is based on tree ring analysis (dendrogeomorphology). The detection of landslide movements is based on dating growth responses induced by slope movements. To date, a relatively limited spectrum of tree growth disturbances has been used in landslide research. This study provides new evidence about the possibilities of using tension wood (a growth response to stem tilting) in Fagus sylvatica L. for detection of past landslide movements. Twenty-three disturbed trees growing on a landslide with a known origin (July 1997) were analysed. Parameters of the tension wood and tree rings (vessel lumen area (VLA) and its change, the duration of tension wood, and tree ring eccentricity and its change) were compared with each other and with tree parameters (tilting degree, age, and stem diameter). Tension wood was readily macroscopically identified on the prepared surfaces of increment cores using a stereoscope. Significant relationships were found between the degree of stem tilting and tension wood duration and the magnitude of VLA change. Thus, these two parameters of tension wood can be viewed as potential indicators of landslide-influenced intensity. Tension wood formation seems to be very sensitive to tree stem tilting, as all studied trees with various degrees of stem tilting contained it in the entire tree ring width after 1997. Moreover, the onset of tension wood in 1997 always started in the second part of the tree ring width. This signals the immediate growth response to landslide movements and the possibility of using tension wood for dating with sub-annual (seasonal) resolution. Tree ring eccentricity correlated with the stem tilting degree as well; nevertheless, no relationship with tension wood parameters was found. The findings of this study with the discussed limits provide support for the very effective use of tension wood in the dendrogeomorphology of landslides.

Vertical variability of tension wood formation in the stem of Fagus sylvatica L. affected by landslide movement

Vertical variability of tension wood formation in the stem of Fagus sylvatica L. affected by landslide movement

Genome-wide analysis of lncRNA and mRNA expression and endogenous hormone regulation during tension wood formation in Catalpa bungei

BackgroundPhytohormones are the key factors regulating vascular development in plants, and they are also involved in tension wood (TW) formation. Although the theory of hormone distribution in TW formation is widely supported, the effects of endogenous hormones on TW formation have not yet been assessed. In this study, TW formation was induced in Catalpa bungei by artificial bending. The phytohormone content of TW, opposite wood (OW) and normal wood (NW) was determined using liquid chromatography-mass spectrometry (LC-MS), and transcriptome sequencing was performed. The hormone content and related gene expression data were comprehensively analyzed.ResultsThe results of analyses of the plant hormone contents indicated significantly higher levels of cis-zeatin (cZ), indoleacetic acid (IAA) and abscisic acid (ABA) in TW than in OW. Genes involved in the IAA and ABA synthesis pathways, such as ALDH (evm.model.group5.1511) and UGT (evm.model.scaffold36.20), were significantly upregulated in TW. and the expression levels of ARF (evm.model.group5.1332), A-ARR (evm.model.group0.1600), and TCH4 (evm.model.group2.745), which participate in IAA, cZ and Brassinolide (BR) signal transduction, were significantly increased in TW. In particular, ARF expression may be regulated by long noncoding RNAs (lncRNAs) and the HD-ZIP transcription factor ATHB-15.ConclusionsWe constructed a multiple hormone-mediated network of C. bungei TW formation based on hormone levels and transcriptional expression profiles were identified during TW formation.

PtiCYP85A3, a BR C-6 Oxidase Gene, Plays a Critical Role in Brassinosteroid-Mediated Tension Wood Formation in Poplar.

In angiosperm trees, the gelatinous layer (G-layer) takes a great part of the fiber cell wall in the tension wood (TW). However, the mechanism underlying G-layer formation in poplar is largely unknown. In this work, we demonstrate that G-layer formation in poplar TW cells is regulated by brassinosteroid (BR) and its signaling. PtiCYP85A3, a key BR biosynthesis gene, was predominantly expressed in the xylem of TW, accompanied with a relatively higher castasterone (CS) accumulation, than in the xylem of opposite wood (OW). A wider expression zone of BZR1, a key transcriptional factor in BR singling pathway, was also observed in G-fiber cells on TW side than in wood fiber cells on the OW side, as indicated by immunohistochemistry assays. Transgenic poplar plants overexpressing PtiCYP85A3 produced thicker G-layer with higher cellulose proportion, and accumulated more BZR1 protein in the xylem of TW than did the wild type (WT) plants. Expression of most TW-associated CesAs, which were induced by 2, 4-epibrassinolide, an active BR, and inhibited by brassinazole, a BR biosynthesis inhibitor, were also up-regulated in the xylem of TW in transgenic plants compared to that in WT plants. Further studies with dual-luciferase assays demonstrated that the promoters of PtiCesAs were activated by PtiMYB128, a TW specific transcription factor, which was then regulated by BZR1. All these results indicate that BR plays a crucial role in the G-layer formation of TW fiber cells by regulating the expression of BZR1, PtiMYB128, and PtiCesAs in poplar.