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Xylem plasticity is important for trees to coordinate hydraulic efficiency and safety under changing soil water availability. However, the physiological and transcriptional regulations of cambium on xylem plasticity are not well understood. In this study, mulberry saplings of drought-resistant Wubu and drought-susceptible Zhongshen1 were subjected to moderate or severe drought stresses for 21 days and subsequently rewatered for 12 days. The anatomical, physiological and transcriptional responses in wood and cambium were analyzed. Most parameters were not affected significantly under moderate drought for both cultivars. Severe drought led to decreased vessel lumen diameter and increased vessel frequency, increased starch and hemicellulose in wood of both cultivars. Notably, increased soluble sugars and lignin were detected only in wood of Wubu. In cambial zone, levels of starch, glucose, fructose, mannose and cytokinin were decreased in both cultivars, whereas soluble sugars were increased in Wubu but deceased in Zhongshen1. RNA-sequencing identified 1824 and 2471 differentially expressed genes in Wubu and Zhongshen1 under severe drought, respectively. These responses were partially recovered after rewatering. Weighted gene correlation network analysis identified modules of co-expressed genes correlated with the anatomical and physiological traits of wood and cambium, with the turquoise and green modules most strongly correlated with traits under drought or rewatering. These modules were enriched in gene ontology terms related to cell division, cytoskeleton organization, cell wall modification, dark respiration, vesicle transport and protein metabolism. Detailed gene expression patterns indicate that reprogramming of cambium activity was relatively similar in both cultivars, but at different scales. These findings provide important insights into the physiological and molecular mechanisms underlying xylem plasticity based on cambium and offer valuable references for breeding drought-resistant mulberry and other woody species in light of future drier climate scenarios. [ABSTRACT FROM AUTHOR]

Summary Lignin, a major wood component, is the key limiting factor for wood conversion efficiency. Its biosynthesis is controlled by transcriptional regulatory networks involving transcription factor (TF)–DNA interactions. However, the epigenetic mechanisms underlying these interactions in lignin biosynthesis remain largely unknown. Here, using yeast one‐hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays, we identified that PtrbZIP44‐A1, a key wood‐forming TF, directly interacts with the promoters of PtrCCoAOMT2 and PtrCCR2, genes involved in the monolignol biosynthetic pathway. We used yeast two‐hybrid, bimolecular fluorescence complementation, biochemical analyses, transient and CRISPR‐mediated transgenesis in Populus trichocarpa to demonstrate that PtrHDA15, a histone deacetylase, acts as an epigenetic inhibitor and is recruited by PtrbZIP44‐A1 for chromatin histone modifications to repress PtrCCoAOMT2 and PtrCCR2, leading to reduced lignin deposition. In transgenic lines overexpressing PtrbZIP44‐A1 or PtrHDA15, histone acetylation at the promoters of PtrCCoAOMT2 and PtrCCR2 decreased, reducing their expression and lignin content. Conversely, in loss‐of‐function ptrbzip44‐a1 and ptrhda15 mutants, histone acetylation levels at PtrCCoAOMT2 and PtrCCR2 promoters increased, enhancing target gene expression and lignin content. Our study uncovered an epigenetic mechanism that suppresses lignin biosynthesis. This finding may help fill a knowledge gap between epigenetic regulation and lignin biosynthesis during wood formation in Populus. [ABSTRACT FROM AUTHOR]

Key message: Oriental beech trees in Hyrcanian forests may exhibit a bimodal growth pattern. While water availability does not limit growth, these trees benefit from warmer weather. Climate projections for the Hyrcanian forests predict higher temperatures and reduced rainfall. However, the impact of these changes on beech tree growth is still debated. This study investigates the intra-annual growth patterns of Oriental beech (Fagus orientalis Lipsky) and their responses to climatic variation within the Hyrcanian forests of northern Iran. We collected micro-cores from six healthy trees in the Sangdeh forest every week from March to September 2022. Microsections were prepared from each core, and the width of the developing tree ring was measured under an optical microscope. We fitted a generalized additive model (GAM) to the measured radial growth increments to model growth and derive daily growth rates. We then used correlations between daily tree growth rates and climatic variables considering different time lags. The results show variable growth patterns within the beech trees, including both unimodal and bimodal growth dynamics during the growing season. Analysis of climatic data indicates a significant positive correlation between temperature and growth rate, particularly with a 15-day lag, while rainfall and humidity exhibit weaker, negative correlations with growth. Surprisingly, sufficient rainfall in the study area may hinder growth due to associated cloud cover, which limits sunshine and photosynthesis. A comparison of variations in radial growth and temperature shows their tight synchronization over the growing season. In conclusion, this study offers insights into the complex interactions between climatic factors and tree growth, with implications for regional forest management and climate change adaptation strategies. [ABSTRACT FROM AUTHOR]

In conifers, compression wood (CW) with a high lignin content forms at the base of the stem or branch in response to gravity, which is a good model system for studying lignin-rich wood formation. In this study, we identified and characterized the laccase gene family (PdeLAC) in Korean red pine (Pinus densiflora), which is integral to monolignol polymerization. Phylogenetic analysis of 54 PdeLAC genes with those from gymnosperms (i.e., Pinus taeda and Picea abies) and angiosperms (i.e., Populus trichocarpa, Arabidopsis thaliana, and Oryza sativa) revealed their categorization into five groups, highlighting distinct evolutionary relationships compared to angiosperms. Gene structure and motif analysis showed conserved copper-binding loops and variable substrate-binding loops, suggesting functional diversity. Expression profiling indicated that 23 PdeLAC genes, including three (PdeLAC28, PdeLAC1, and PdeLAC31) homologous to AtLAC17, were upregulated in developing xylem during the growing season, particularly in CW. Transgenic poplars overexpressing PdeLAC28 exhibited increased xylem area, cell wall thickness, and Klason lignin content, underscoring its role in lignin biosynthesis and CW formation. This study provides valuable insights into the molecular regulation of lignin biosynthesis in CW of P. densiflora, setting a foundation for advancing our understanding of wood formation mechanisms in gymnosperms. [ABSTRACT FROM AUTHOR]

Introduction: Wood formation is a crucial developmental stage in the life cycle of a woody plant; this process has substantial scientific research implications and practical applications. However, the mechanisms underlying woody plant development, especially the process of wood formation, remain poorly understood. As eucalyptus is one of the fastest growing tree species in the world, understanding the mechanism of wood formation in eucalyptus will greatly promote the development of molecular breeding technology for forest trees. Results: In this study, we investigated the proteomic profile of immature xylem at four different ages of Eucalyptus urophylla × Eucalyptus grandis (E. urograndis) using iTARQ technology. We identified 5236 proteins and 492 differentially abundant proteins (DAPs). The expression profiles of the DAPs corresponding to coding genes associated with wood formation were assessed using qRT-PCR. From the different expression profiles, it is inferred that the genes encoding kinesin, CDKD3, EXPA13, EXPA2, XTH27, EGases, UGT76E2, LAC, CCoAMT, CesA3, PAL, and CAD may undergo posttranscriptional regulation (PTR). Additionally, the genes encoding EIN2, ETR, MC4-like, and XCP may undergo posttranslational modifications (PTMs). Conclusions: We investigated changes in wood formation-related proteins at the protein abundance level in the immature xylem of E. urograndis , thereby elucidating potential regulatory mechanisms of key proteins involved in eucalyptus wood formation. This study may provide theoretical guidance for further research on molecular breeding techniques and genetic improvement related to the cultivation of rapidly growing and high-quality trees. [ABSTRACT FROM AUTHOR]

The process-based xylem formation model is an important tool for understanding the radial growth process of trees and its influencing factors. While numerous xylogenesis models for conifers have been developed, there is a lack of models available for non-coniferous trees. In this study, we present a process-based model designed for xylem formation and ring growth in broad-leaved trees, which we call the Broad-leaved Tree-Ring (BTR) model. Climate factors, including daylength, air temperature, soil moisture and vapor pressure deficit, drive daily xylem cell production (fibers and vessels) and growth (enlargement, wall deposition). The model calculates the total cell area in the simulated zone to determine the annual ring width. The results demonstrate that the BTR model can basically simulate inter-annual variation in ring width and intra-annual changes in vessel and fiber cell formation in Fraxinus mandshurica (ring-porous) and Betula platyphylla (diffuse-porous). The BTR model is a potential tool for understanding how different trees form wood and how climate change influences this process. [ABSTRACT FROM AUTHOR]

Taxodium ascendens has been extensively cultivated in the wetlands of the Yangtze River in south China and has significantly contributed to ecology and timber production. Until now, research on T. ascendens genomics has yet to be conducted due to its large and complex genome, which hinders the development of T. ascendens genomic resources. Combined with the microstructural changes during cambium cell differentiation across various growth periods, we investigate the transcriptome expression and regulatory mechanisms governing cambium activity in T. ascendens. Using RNA sequencing (RNA-Seq) technology, we identified the genes involved in the cambium development of cells at three stages (dormancy, reactivation, and activity). These genes encode the regulatory and control factors associated with the cambial activity, cell division, cell expansion, and biosynthesis of cell wall components. Blast comparison revealed that three genes (TR_DN69961_c0_g1, TRINITY_DN17100_c1_g1, TRINITY_DN111727_c0_g1) from the MYB and NAC families might regulate transcription during lignin formation in wood thickening. These results illustrate the dynamic changes in the transcriptional network during vascular cambium development. Additionally, they shed light on the genetic regulation mechanism of secondary growth in T. ascendens and guide further elucidation of the candidate genes involved in regulating cambium differentiation and wood formation.

The year 2018 was distinguished by a warm summer with extended periods of low or no precipitation. In this context, we investigated the intra-annual dynamics of xylem differentiation phases and quantitative vessel anatomy to analyse the age effect on the xylem formation response of younger (50 years) and older (135 years) mature European beech trees under summer drought conditions. The xylem formation dynamics of young and old trees were performed on microcores collected at weekly intervals in the Rájec-Němčice ecological station in the South Moravia region (Czech Republic). The onset of xylem formation was found identical in both age trees, and most of the trees ceased their enlargement by the end of July, which is attributed to the harsh environmental conditions of this month. Young trees were characterised by a 10-day extended enlargement period and a higher growth rate, resulting in more vessels and a wider tree-ring width. No significant linkage was found between intra-annual environmental conditions of the 2018 year or age effect and the vessel anatomy traits.

Summary: The genetic control underlying natural variation in lignin content and composition in trees is not fully understood. We performed a systems genetic analysis to uncover the genetic regulation of lignin biosynthesis in a natural 'SwAsp' population of aspen (Populus tremula) trees.We analyzed gene expression by RNA sequencing (RNA‐seq) in differentiating xylem tissues, and lignin content and composition using Pyrolysis‐GC‐MS in mature wood of 268 trees from 99 genotypes.Abundant variation was observed for lignin content and composition, and genome‐wide association study identified proteins in the pentose phosphate pathway and arabinogalactan protein glycosylation among the top‐ranked genes that are associated with these traits. Variation in gene expression and the associated genetic polymorphism was revealed through the identification of 312 705 local and 292 003 distant expression quantitative trait loci (eQTL). A co‐expression network analysis suggested modularization of lignin biosynthesis and novel functions for the lignin‐biosynthetic CINNAMYL ALCOHOL DEHYDROGENASE 2 and CAFFEOYL‐CoA O‐METHYLTRANSFERASE 3. PHENYLALANINE AMMONIA LYASE 3 was co‐expressed with HOMEOBOX PROTEIN 5 (HB5), and the role of HB5 in stimulating lignification was demonstrated in transgenic trees.The systems genetic approach allowed linking natural variation in lignin biosynthesis to trees´ responses to external cues such as mechanical stimulus and nutrient availability. [ABSTRACT FROM AUTHOR]

Tropical montane evergreen broad-leaved forests cover the majority of forest areas and have high carbon storage in Xishuangbanna, southwest China. However, stem radial growth dynamics and their correlations with climate factors have never been analyzed in this forest type. By combining bi-weekly microcoring and high-resolution dendrometer measurements, we monitored xylogenesis and stem radius variations of the deciduous species Betula alnoides Buch.-Ham. ex D. Don and the evergreen species Schima wallichii (DC.) Korth. We analyzed the relationships between weekly climate variables prior to sampling and the enlarging zone width or wall-thickening zone width, as well as weekly radial increments and climate factors during two consecutive years (2020 to 2021) showing contrasting hydrothermal conditions in the pre-monsoon season. In the year 2020, which was characterized by a warmer and drier pre-monsoon season, the onset of xylogenesis and radial increments of B. alnoides and S. wallichii were delayed by three months and one month, respectively, compared with the year 2021. In 2020, xylem formation and radial increments were significantly reduced for B. alnoides , but not for S. wallichii. The thickness of enlarging zone and wall-thickening zone in S. wallichii were positively correlated with relative humidity, and minimum and mean air temperature, but were negatively correlated with vapor pressure deficit during 2020 to 2021. The radial increments of both species showed significant positive correlations with precipitation and relative humidity, and negative correlations with vapor pressure deficit and maximum air temperature during two years. Our findings reveal that drier pre-monsoon conditions strongly delay growth initiation and reduce stem radial growth, providing deep insights to understand tree growth and carbon sequestration potential in tropical forests under a predicted increase in frequent drought events. [ABSTRACT FROM AUTHOR]

The year 2018 was distinguished by a warm summer with extended periods of low or no precipitation. In this context, we investigated the intra-annual dynamics of xylem differentiation phases and quantitative vessel anatomy to analyse the age effect on the xylem formation response of younger (50 years) and older (135 years) mature European beech trees under summer drought conditions. The xylem formation dynamics of young and old trees were performed on microcores collected at weekly intervals in the Rájec-Němčice ecological station in the South Moravia region (Czech Republic). The onset of xylem formation was found identical in both age trees, and most of the trees ceased their enlargement by the end of July, which is attributed to the harsh environmental conditions of this month. Young trees were characterised by a 10-day extended enlargement period and a higher growth rate, resulting in more vessels and a wider tree-ring width. No significant linkage was found between intra-annual environmental conditions of the 2018 year or age effect and the vessel anatomy traits. [ABSTRACT FROM AUTHOR]

Summary: Wood is resulted from the radial growth paced by the division and differentiation of vascular cambium cells in woody plants, and phytohormones play important roles in cambium activity.Here, we identified that PagJAZ5, a key negative regulator of jasmonate (JA) signaling, plays important roles in enhancing cambium cell division and differentiation by mediating cytokinin signaling in poplar 84K (Populus alba × Populus glandulosa).PagJAZ5 is preferentially expressed in developing phloem and cambium, weakly in developing xylem cells. Overexpression (OE) of PagJAZ5m (insensitive to JA) increased cambium activity and xylem differentiation, while jaz mutants showed opposite results. Transcriptome analyses revealed that cytokinin oxidase/dehydrogenase (CKXs) and type‐A response regulators (RRs) were downregulated in PagJAZ5m OE plants. The bioactive cytokinins were significantly increased in PagJAZ5m overexpressing plants and decreased in jaz5 mutants, compared with that in 84K plants. The PagJAZ5 directly interact with PagMYC2a/b and PagWOX4b. Further, we found that the PagRR5 is regulated by PagMYC2a and PagWOX4b and involved in the regulation of xylem development.Our results showed that PagJAZ5 can increase cambium activity and promote xylem differentiation through modulating cytokinin level and type‐A RR during wood formation in poplar. [ABSTRACT FROM AUTHOR]

Summary: Wood formation, which occurs mainly through secondary xylem development, is important not only for supplying raw material for the 'ligno‐chemical' industry but also for driving the storage of carbon. However, the complex mechanisms underlying the promotion of xylem formation remain to be elucidated. Here, we found that overexpression of Auxin‐Regulated Gene involved in Organ Size (ARGOS) in hybrid poplar 84 K (Populus alba × Populus tremula var. glandulosa) enlarged organ size. In particular, PagARGOS promoted secondary growth of stems with increased xylem formation. To gain further insight into how PagARGOS regulates xylem development, we further carried out yeast two‐hybrid screening and identified that the auxin transporter WALLS ARE THIN1 (WAT1) interacts with PagARGOS. Overexpression of PagARGOS up‐regulated WAT1, activating a downstream auxin response promoting cambial cell division and xylem differentiation for wood formation. Moreover, overexpressing PagARGOS caused not only higher wood yield but also lower lignin content compared with wild‐type controls. PagARGOS is therefore a potential candidate gene for engineering fast‐growing and low‐lignin trees with improved biomass production. [ABSTRACT FROM AUTHOR]

The biosynthesis of cellulose, lignin, and hemicelluloses in plant secondary cell walls (SCWs) is regulated by a hierarchical transcriptional regulatory network. This network features orthologous transcription factors shared between poplar and Arabidopsis, highlighting a foundational similarity in their genetic regulation. However, knowledge on the discrepant behavior of the transcriptional‐level molecular regulatory mechanisms between poplar and Arabidopsis remains limited. In this study, we investigated the function of PagMYB128 during wood formation and found it had broader impacts on SCW formation compared to its Arabidopsis ortholog, AtMYB103. Transgenic poplar trees overexpressing PagMYB128 exhibited significantly enhanced xylem development, with fiber cells and vessels displaying thicker walls, and an increase in the levels of cellulose, lignin, and hemicelluloses in the wood. In contrast, plants with dominant repression of PagMYB128 demonstrated the opposite phenotypes. RNA sequencing and reverse transcription – quantitative polymerase chain reaction showed that PagMYB128 could activate SCW biosynthetic gene expression, and chromatin immunoprecipitation along with yeast one‐hybrid, and effector–reporter assays showed this regulation was direct. Further analysis revealed that PagSND1 (SECONDARY WALL‐ASSOCIATED NAC‐DOMAIN PROTEIN1) directly regulates PagMYB128 but not cell wall metabolic genes, highlighting the pivotal role of PagMYB128 in the SND1‐driven regulatory network for wood development, thereby creating a feedforward loop in SCW biosynthesis. [ABSTRACT FROM AUTHOR]

Key message: Despite the better performance in wood growth compared with Siberian larch, Siberian spruce may be more vulnerable to ongoing climate change. Understanding the species-specific wood formation kinetics is critical to assess forest growth and carbon sequestration under climate warming; however, such knowledge is still scarce in the fragile forest ecosystems of arid and semi-arid central Asia. Here, we monitored wood formation in two dominant tree species Siberian spruce (Picea obovata Ledeb.) and Siberian larch (Larix sibirica Ledeb.) during 2018 and 2019 at two sites in the southern Altai Mountains, northwest China, and aimed to describe the intra-annual dynamics of wood formation and to understand the annual variation in growth and carbon sequestration of these two species. Results show that the differences in wood production between species were remarkable. Siberian spruce produced 68.5–87.6 cells year−1 at an average rate of 0.82–0.95 cells day−1, about twofold higher than Siberian larch. The differences between species in terms of the onset, cessation timing, and duration of cell production were marginal. Cell production of both species started from mid-May to early June, ceased from early to mid-August, and lasted for about 64 to 70 days. The higher growth rate of spruce led to greater wood production compared to larch. The longer growing seasons induced by climate warming may not result in increased forest growth, thereby failing to enhance carbon sequestration in arid and semi-arid taiga of Central Asia. [ABSTRACT FROM AUTHOR]

Quercus ilex L., an evergreen oak species typical of the western and central Mediterranean basin, is facing decline and dieback episodes due to the increase in the severity and frequency of heat waves and drought events. Studying xylogenesis (the wood formation process) is crucial for understanding how trees respond with their secondary growth to environmental conditions and stress events. This study aimed to characterize the wood formation dynamics of Quercus ilex and their relationship with the meteorological conditions in an area experiencing prolonged drought periods. Cambial activity and xylem cell production were monitored during the 2019 and 2020 growing seasons in a Q. ilex forest located at the Vesuvius National Park (southern Italy). The results highlighted the significant roles of temperature and solar radiation in stimulating xylogenesis. Indeed, the correlation tests revealed that temperature and solar radiation positively influenced growth and cell development, while precipitation had an inhibitory effect on secondary wall formation. The earlier cell maturation in 2020 compared to 2019 underscored the impact of global warming trends. Overall, the trees studied demonstrated good health, growth and adaptability to local environmental fluctuations. This research provides novel insights into the intra-annual growth dynamics of this key Mediterranean species and its adaptation strategies to climatic variability, which will be crucial for forest management in the context of climate change. [ABSTRACT FROM AUTHOR]

Xylem plasticity is important for trees to coordinate hydraulic efficiency and safety under changing soil water availability. However, the physiological and transcriptional regulations of cambium on xylem plasticity are not well understood. In this study, mulberry saplings of drought-resistant Wubu and drought-susceptible Zhongshen1 were subjected to moderate or severe drought stresses for 21 days and subsequently rewatered for 12 days. The anatomical, physiological and transcriptional responses in wood and cambium were analyzed. Most parameters were not affected significantly under moderate drought for both cultivars. Severe drought led to decreased vessel lumen diameter and increased vessel frequency, increased starch and hemicellulose in wood of both cultivars. Notably, increased soluble sugars and lignin were detected only in wood of Wubu. In cambial zone, levels of starch, glucose, fructose, mannose and cytokinin were decreased in both cultivars, whereas soluble sugars were increased in Wubu but deceased in Zhongshen1. RNA-sequencing identified 1824 and 2471 differentially expressed genes in Wubu and Zhongshen1 under severe drought, respectively. These responses were partially recovered after rewatering. Weighted gene correlation network analysis identified modules of co-expressed genes correlated with the anatomical and physiological traits of wood and cambium, with the turquoise and green modules most strongly correlated with traits under drought or rewatering. These modules were enriched in gene ontology terms related to cell division, cytoskeleton organization, cell wall modification, dark respiration, vesicle transport and protein metabolism. Detailed gene expression patterns indicate that reprogramming of cambium activity was relatively similar in both cultivars, but at different scales. These findings provide important insights into the physiological and molecular mechanisms underlying xylem plasticity based on cambium and offer valuable references for breeding drought-resistant mulberry and other woody species in light of future drier climate scenarios.

There is a growing demand for wood as a sustainable energy source and an essential carbon sink for ecosystems. Wood formation is a dynamic process involving plant radial growth in various stages, including vascular cambial cell proliferation, xylem mother cell differentiation and expansion, secondary cell wall thickening, and programmed cell death. Wood formation is controlled by highly complex molecular regulatory networks. Identifying and analyzing the molecular mechanisms regulating key target genes is crucial for further characterizing how wood is formed. This article summarizes the current knowledge regarding wood formation and the underlying molecular regulatory mechanisms.

Background and Aims Secondary cell wall (SCW) thickening is a major cellular developmental stage determining wood structure and properties. Although the molecular regulation of cell wall deposition during tracheary element differentiation has been well established in primary growth systems, less is known about the gene regulatory processes involved in the multi-layered SCW thickening of mature trees. Methods Using third-generation [long-read single-molecule real-time (SMRT)] and second-generation [short-read sequencing by synthesis (SBS)] sequencing methods, we established a Pinus bungeana transcriptome resource with comprehensive functional and structural annotation for the first time. Using these approaches, we generated high spatial resolution datasets for the vascular cambium, xylem expansion regions, early SCW thickening, late SCW thickening and mature xylem tissues of 71-year-old Pinus bungeana trees. Key Results A total of 79 390 non-redundant transcripts, 31 808 long non-coding RNAs and 5147 transcription factors were annotated and quantified in different xylem tissues at all growth and differentiation stages. Furthermore, using this high spatial resolution dataset, we established a comprehensive transcriptomic profile and found that members of the NAC, WRKY, SUS, CESA and LAC gene families are major players in early SCW formation in tracheids, whereas members of the MYB and LBD transcription factor families are highly expressed during late SCW thickening. Conclusions Our results provide new molecular insights into the regulation of multi-layered SCW thickening in conifers. The high spatial resolution datasets provided can serve as important gene resources for improving softwoods. [ABSTRACT FROM AUTHOR]

Wood is an abundant and essential renewable resource whose production is threatened in some parts of the world by drought. A better understanding of the molecular mechanisms underlying wood formation during drought is critical to maintaining wood production under increasingly adverse environmental conditions. In this study, we investigated wood formation in black cottonwood (Populus trichocarpa) during drought stress. The morphological changes during drought stress in P. trichocarpa included the wilting and drooping of leaves, stem water loss, and a reduction in whole plant biomass. The water embolism rate indicated that the water transport in stems was blocked under drought conditions. An anatomical analysis of the xylem and cambium revealed that drought stress changed the structure of vessel cells, increased lignin accumulation, and decreased the cambium cell layers. We subsequently identified 12,438 and 9156 differentially expressed genes from stem xylem and cambium tissues under well-watered and drought conditions, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that these genes were mainly involved in hormone signal transduction and amino sugar and nucleotide sugar metabolism. To further explore the molecular mechanism of wood formation in response to drought, we analyzed the expression patterns of the genes involved in lignin, cellulose, and hemicellulose biosynthesis in xylem and the genes involved in cambial activity in the cambium. To better understand the regulatory networks governing xylem development and cambium activity in response to drought, we analyzed the MYB (138), AP2 (130), bHLH (89), and NAC (81) transcription factor families to shed light on the interactions between the TFs in these families and the genes they regulate. Identifying the key genes that regulate wood formation in P. trichocarpa during drought provides a genetic foundation for further research on the molecular regulatory networks and physiology underpinning wood formation during drought stress. [ABSTRACT FROM AUTHOR]

IntroductionWood formation is a crucial developmental stage in the life cycle of a woody plant; this process has substantial scientific research implications and practical applications. However, the mechanisms underlying woody plant development, especially the process of wood formation, remain poorly understood. As eucalyptus is one of the fastest growing tree species in the world, understanding the mechanism of wood formation in eucalyptus will greatly promote the development of molecular breeding technology for forest trees.ResultsIn this study, we investigated the proteomic profile of immature xylem at four different ages of Eucalyptus urophylla × Eucalyptus grandis (E. urograndis) using iTARQ technology. We identified 5236 proteins and 492 differentially abundant proteins (DAPs). The expression profiles of the DAPs corresponding to coding genes associated with wood formation were assessed using qRT-PCR. From the different expression profiles, it is inferred that the genes encoding kinesin, CDKD3, EXPA13, EXPA2, XTH27, EGases, UGT76E2, LAC, CCoAMT, CesA3, PAL, and CAD may undergo posttranscriptional regulation (PTR). Additionally, the genes encoding EIN2, ETR, MC4-like, and XCP may undergo posttranslational modifications (PTMs).ConclusionsWe investigated changes in wood formation-related proteins at the protein abundance level in the immature xylem of E. urograndis, thereby elucidating potential regulatory mechanisms of key proteins involved in eucalyptus wood formation. This study may provide theoretical guidance for further research on molecular breeding techniques and genetic improvement related to the cultivation of rapidly growing and high-quality trees.

Abstract Background Alternative polyadenylation (APA), alternative splicing (AS), and long non-coding RNAs (lncRNAs) play regulatory roles in post-transcriptional processes in plants. However, little is known about their involvement in xylem development in Dalbergia odorifera, a valuable rosewood species with medicinal and commercial significance. We addressed this by conducting Isoform Sequencing (Iso-Seq) using PacBio’s SMRT technology and combined it with RNA-seq analysis (RNA sequencing on Illumina platform) after collecting xylem samples from the transition zone and the sapwood of D. odorifera. Results We identified 14,938 full-length transcripts, including 9,830 novel isoforms, which has updated the D. odorifera genome annotation. Our analysis has revealed that 4,164 genes undergo APA, whereas 3,084 genes encounter AS. We have also annotated 118 lncRNAs. Furthermore, RNA-seq analysis identified 170 differential alternative splicing (DAS) events, 344 genes with differential APA site usage (DE-APA), and 6 differentially expressed lncRNAs in the transition zone when compared to the sapwood. AS, APA, and lncRNAs are differentially regulated during xylem development. Differentially expressed APA genes were enriched for terpenoid and flavonoid metabolism, indicating their role in the heartwood formation. Additionally, DE-APA genes were associated with cell wall biosynthesis and terpenoid metabolism, implying an APA’s role in wood formation. A DAS gene (involved in chalcone accumulation) with a significantly greater inclusion of the last exon in the transition zone than in the sapwood was identified. We also found that differentially expressed lncRNAs targeted the genes related to terpene synthesis. Conclusions This study enhances our understanding of the molecular regulatory mechanisms underlying wood formation in D. odorifera, and provides valuable genetic resources and insights for its molecular-assisted breeding.

Abstract Background Dalbergia odorifera is a rare and precious rosewood specie, which is valued for its amber tones, abstract figural patterns, and impermeability to water and insects. However, the information on genetic diversity and marker-assisted selection breeding of D. odorifera is still limited. Simple sequence repeat (SSR) markers are an ideal tool for genetic diversity analysis and marker-assisted molecular breeding for complex traits. Results Here, we have developed SSR markers within candidate genes and used them to explore the genetic diversity among D. odorifera germplasm resources. A total of 635 SSR loci were identified. The proportions of mono-, di- and tri-nucleotide repeat motifs were 52.28%, 22.99% and 21.42%, respectively. From these, a total of 114 SSR primers were synthesized, of which 24 SSR markers displayed polymorphism (polymorphic information content (PIC) > 0.25). Subsequently, these polymorphic markers were used for the genetic diversity analysis of 106 D. odorifera individuals from 11 natural populations. According to the genetic diversity analysis of D. odorifera natural populations, the average observed heterozygosity (Ho) was 0.500, the average expected heterozygosity (He) was 0.524, and the average Shannon’s information index (I) was 0.946. These indicated that the natural populations had moderate genetic diversity. AMOVA analysis showed that 5% of the total variation was within the individuals of a population, whereas 95% of the variation was among the individuals of the populations, indicating a high degree of genetic variation between populations. On the basis of their genetic structures, these populations could be divided into four groups. Conclusions Our study provides important experimental resources for genetic studies and assists in the program of molecular breeding of D. odorifera wood formation.

Abstract Eucalyptus was one of the most cultivated hardwood species worldwide, with rapid growth, good wood properties and a wide range of adaptability. Eucalyptus stem undergoes primary growth (longitudinal growth) followed by secondary growth (radial growth), which produces biomass that is an important source of energy worldwide. In order to better understand the genetic regulation of secondary growth in Eucalyptus grandis, Transcriptome analyses in stem segments along a developmental gradient from the third internode to the eleventh internode of E. grandis that spanned primary to secondary growth were carried out. 5,149 genes that were differentially expressed during stem development were identified. Combining the trend analysis by the Mfuzz method and the module-trait correlation analysis by the Weighted Gene Co-expression Network Analysis method, a total of 70 differentially expressed genes (DEGs) selected from 868 DEGs with high connectivity were found to be closely correlated with secondary growth. Results revealed that the differential expression of these DEGs suggests that they may involve in the primary growth or secondary growth. AP1, YAB2 TFs and EXP genes are highly expressed in the IN3, whereas NAC, MYB TFs are likely to be important for secondary growth. These results will expand our understanding of the complex molecular and cellular events of secondary growth and provide a foundation for future studies on wood formation in Eucalyptus.

Background Alternative polyadenylation (APA), alternative splicing (AS), and long non-coding RNAs (lncRNAs) play regulatory roles in post-transcriptional processes in plants. However, little is known about their involvement in xylem development in Dalbergia odorifera, a valuable rosewood species with medicinal and commercial significance. We addressed this by conducting Isoform Sequencing (Iso-Seq) using PacBio's SMRT technology and combined it with RNA-seq analysis (RNA sequencing on Illumina platform) after collecting xylem samples from the transition zone and the sapwood of D. odorifera. Results We identified 14,938 full-length transcripts, including 9,830 novel isoforms, which has updated the D. odorifera genome annotation. Our analysis has revealed that 4,164 genes undergo APA, whereas 3,084 genes encounter AS. We have also annotated 118 lncRNAs. Furthermore, RNA-seq analysis identified 170 differential alternative splicing (DAS) events, 344 genes with differential APA site usage (DE-APA), and 6 differentially expressed lncRNAs in the transition zone when compared to the sapwood. AS, APA, and lncRNAs are differentially regulated during xylem development. Differentially expressed APA genes were enriched for terpenoid and flavonoid metabolism, indicating their role in the heartwood formation. Additionally, DE-APA genes were associated with cell wall biosynthesis and terpenoid metabolism, implying an APA’s role in wood formation. A DAS gene (involved in chalcone accumulation) with a significantly greater inclusion of the last exon in the transition zone than in the sapwood was identified. We also found that differentially expressed lncRNAs targeted the genes related to terpene synthesis. Conclusions This study enhances our understanding of the molecular regulatory mechanisms underlying wood formation in D. odorifera, and provides valuable genetic resources and insights for its molecular-assisted breeding. [ABSTRACT FROM AUTHOR]

Key message: Cortical microtubule arrays are the primary mechanism for guiding the re-orientation of cellulose microfibrils and determining MFA in secondary cell wall of wood fibre and tracheid cells in reaction wood. Microtubules are directly and indirectly involved in guiding cellulose synthase complexes (CSCs) through the plasma membrane. The angle of cellulose deposition is a critical response to environmental signals and/or stress conditions, and particularly crucial during reaction wood formation, a process in which woody plants deposit additional cell wall material to counteract gravitational forces. Tubulin genes are upregulated in response to gravitational stimulus during reaction wood formation, which can result in changes to microtubule assembly. In this study, microtubules were visualised in three woody tree species (two angiosperms: Eucalyptus globulus Labill., Populus alba L., and one gymnosperm: Pinus radiata D. Don.) using immunofluorescence to quantitatively evaluate microtubule organisation during reaction wood formation. Our results suggest that reorientation of the cortical microtubule array affects secondary cell wall deposition, even across different types of reaction wood, by ensuring context-appropriate orientation of cellulose microfibrils and determining MFA in wood cells. Pharmacological studies conducted on in vitro cultured stem segments or in vivo during reaction wood formation corroborated these important roles for microtubules during wood development. This study starts to unveil the role of tubulins during wood formation by exploring cortical microtubule array organisation in trees subjected to gravitational stimulus and it sheds light on cellular and molecular mechanisms behind cellulose deposition in tree species. [ABSTRACT FROM AUTHOR]

The critical role of auxin on secondary vascular development in woody plants has been demonstrated. The concentration gradient of endogenous indole-3-acetic acid and the cellular and molecular pathways contributing to the auxin-directed vascular organization and wood growth have been uncovered in recent decades. However, our understanding of the roles and regulations of auxin influx in wood formation in trees remains limited. Here, we reported that a microRNA, miR7833, participates in the negative regulation of stem cambial cell division and secondary xylem development in Populus tomentosa. The miR7833 is mainly expressed in the vascular cambium during stem radical growth and specifically targets and represses two AUX/LAX family auxin influx carriers, AUX5 and AUX6 , in poplar. We further revealed that poplar AUX6 , the most abundant miR7833 target in the stem, is preferentially enriched in the developing xylem and is a positive regulator for cell division and differentiation events during wood formation. Moreover, inhibition of auxin influx carriers by 1-naphthoxyacetic acids abolished the regulatory effects of miR7833 and AUX6 on secondary xylem formation in poplar. Our results revealed the essential roles of the miR7833- AUX6 module in regulating cellular events in secondary xylem development and demonstrated an auxin influx-dependent mechanism for wood formation in poplar. [ABSTRACT FROM AUTHOR]

Wood is an invaluable asset to human society due to its renewable nature, making it suitable for both sustainable energy production and material manufacturing. Additionally, wood derived from forest trees plays a crucial role in sequestering a significant portion of the carbon dioxide fixed during photosynthesis by terrestrial plants. Nevertheless, with the expansion of the global population and ongoing industrialization, forest coverage has been substantially decreased, resulting in significant challenges for wood production and supply. Wood production practices have changed away from natural forests toward plantation forests. Thus, understanding the underlying genetic mechanisms of wood formation is the foundation for developing high‐quality, fast‐growing plantation trees. Breeding ideal forest trees for wood production using genetic technologies has attracted the interest of many. Tremendous studies have been carried out in recent years on the molecular, genetic, and cell‐biological mechanisms of wood formation, and considerable progress and findings have been achieved. These studies and findings indicate enormous possibilities and prospects for tree improvement. This review will outline and assess the cellular and molecular mechanisms of wood formation, as well as studies on genetically improving forest trees, and address future development prospects. [ABSTRACT FROM AUTHOR]

Primary and secondary growth of trees are needed for increments in plant height and stem diameter, respectively, affecting the production of woody biomass for applications in timber, pulp/paper, and related biomaterials. These two types of growth are believed to be both regulated by distinct transcription factor (TF)-mediated regulatory pathways. Notably, we identified PtrLBD39, a highly stem phloem-specific TF in Populus trichocarpa and found that the ectopic expression of PtrLBD39 in P. trichocarpa markedly retarded both primary and secondary growth. In these overexpressing plants, the RNA-seq, ChIP-seq, and weighted gene co-expression network analysis (WGCNA) revealed that PtrLBD39 directly or indirectly regulates TFs governing vascular tissue development, wood formation, hormonal signaling pathways, and enzymes responsible for wood components. This regulation led to growth inhibition, decreased fibrocyte secondary cell wall thickness, and reduced wood production. Therefore, our study indicates that, following ectopic expression in P. trichocarpa, PtrLBD39 functions as a repressor influencing both primary and secondary growth. [ABSTRACT FROM AUTHOR]

Canopy phenology is a widely used proxy for deciduous forest growth with various applications in terrestrial ecosystem modeling. Its use relies on common assumptions that canopy greening and stem growth are tightly coordinated processes, enabling predictions on the timing and the quantity of annual tree growth. Here, we present parallel observations of canopy and stem growth phenology and annual stem increment in around 90 deciduous forest trees with diffuse-porous (Fagus sylvatica , Acer pseudoplatanus , Carpinus betulus) or ring-porous (Quercus robur × petraea) wood anatomy. These data were collected in a mixed temperate forest at the Swiss-Canopy-Crane II site, in 4 years with strongly contrasting weather conditions. We found that stem growth resumption lagged several weeks behind spring canopy greening in diffuse-porous but not in ring-porous trees. Canopy greening and stem growth resumption showed no or only weak signs of temporal coordination across the observation years. Within the assessed species, the seasonal timing of stem growth varied strongly among individuals, as trees with high annual increments resumed growth earlier and also completed their main growth earlier. The length of main growth activity had no influence on annual increments. Our findings not only challenge tight temporal coordination of canopy and stem growth phenology but also demonstrate that longer main growth activity does not translate into higher annual increments. This may compromise approaches modeling tree growth and forest productivity with canopy phenology and growth length. [ABSTRACT FROM AUTHOR]

The development of the tree ring is a process occurring under limitations caused by a complex of environmental factors and intrinsic regulatory mechanisms. Its understanding is of interest in many scientific fields, but most quantitative models trying to describe its details meet several issues stemming from the difficulty of its verification. This study attempted to combine several observational and modeling approaches to verify intermediate details of the description of xylogenesis, aiming to restore the tree-ring seasonal growth kinetics on the basis of dendrochronological and wood anatomical data. It was carried out for Scots pine in two semiarid habitats in South Siberia. The Vaganov-Shashkin model was used jointly with tree-ring width chronology and climatic data to model the tree radial growth rate with daily precision. The Band-model was then used to calculate the kinetics of tracheid production from the growth rate and actual final number of cells per radial file in the ring. Seasonal observations of cell population and final measurements of cell sizes were used to fit model parameters and verify the numbers of developing tracheids produced by the Band-model. The patterns of modeled seasonal kinetics for six seasons and two sites were found to repeat the actual drought-derived deviations in tree growth and observations (R2 = 0.70–0.84). Further research is required to test other climatic limitations and species-specific ecophysiological mechanisms of growth regulation. [ABSTRACT FROM AUTHOR]

Wood density is a crucial factor in determining the quality of wood in boreal ecosystems within the Northern Hemisphere. Climate variables play a significant role in shaping wood density, posing challenges for forest managers and stakeholders in the wood industry to adapt amidst climate change. However, our current understanding of these effects remains incomplete. This systematic literature review explores the multifaceted influences on wood density in the boreal zone, encompassing both climate-related and non-climatic factors. The findings demonstrate that warmer temperatures can cause both increases and decreases in wood density, primarily due to their impact on tracheid lignification and cell wall thickening. Nonetheless, the outcome depends on various factors, including species type, age, soil conditions, presence of pests and diseases, fire, windstorms, and silviculture practices. The quantification of complex relationships between these factors and wood density has been insufficient in existing literature. Understanding the impacts of both climate and non-climate factors on wood density is essential for fostering a sustainable wood industry, while effectively mitigating adverse effects and maximizing benefits. Forest managers can leverage this knowledge to optimize wood production strategies, ensuring long-term ecological resilience amidst the increasingly variable climate challenges.

There is a growing demand for wood as a sustainable energy source and an essential carbon sink for ecosystems. Wood formation is a dynamic process involving plant radial growth in various stages, including vascular cambial cell proliferation, xylem mother cell differentiation and expansion, secondary cell wall thickening, and programmed cell death. Wood formation is controlled by highly complex molecular regulatory networks. Identifying and analyzing the molecular mechanisms regulating key target genes is crucial for further characterizing how wood is formed. This article summarizes the current knowledge regarding wood formation and the underlying molecular regulatory mechanisms. [ABSTRACT FROM AUTHOR]

Summary: In recent years, the popularity of X-ray computed tomography (CT), as a non-destructive imaging technique, has continued to expand in various research domains. In wood research, X-ray CT has proven to be useful for three-dimensional (3D) structural studies investigating the complex tissues of trees. Wood formation (i.e., xylogenesis) initiates in the cambium and a narrow zone of subsequent differentiation, both of which play key roles in plant growth and development. However, the dynamics of xylogenesis in eucalypts remain relatively poorly understood, in large part due to challenges in sampling, imaging, and characterizing the cambium. Therefore, the aim of this study was to present a workflow to evaluate the feasibility of using X-ray CT to characterize and quantify the structural properties of the cambium in eucalypts. The growth responses of Corymbia hybrid seedlings, exposed to either irrigated or droughted conditions, was investigated by monitoring the structural development of the cambium. To track microstructural changes in the cambium, the same seedlings were imaged with X-ray micro-CT (μ CT) one day before the treatments and again six days after the respective treatments. After the last X-ray μ CT scan, X-ray nano-CT was also applied. Using image analysis techniques, the morphological characteristics of the cambium could be determined. X-ray μ CT displayed a larger, thicker cambial zone in irrigated plants, while a much thinner cambium was visible in droughted seedlings. X-ray nano-CT revealed that droughted plants were associated with a significantly (p ⩽ 0.05) smaller cambium volume containing smaller cells, compared to the cambium of irrigated plants. Light microscopy was used to validate the CT results and demonstrated no significant (p > 0.05) difference in the cambium width and cell diameter obtained from the two respective CT techniques. The findings of this study proved X-ray CT to be a valuable tool for examining the effect of changing environmental conditions on the complex cambium structure of Corymbia hybrid seedlings. [ABSTRACT FROM AUTHOR]

A comparative assessment of bud and wood phenology could aid a better understanding of tree growth dynamics. However, the reason for asynchronism or synchronism in leaf and cambial phenology remains unclear. To test the assumption that the temporal relationship between the budburst date and the onset date of wood formation is due to their common or different responses to environmental factors, we constructed a wood phenology dataset from previous literature, and compared it with an existing bud phenology dataset in Europe. We selected three common conifers (Larix decidua Mill. Picea abies (L.) H. Karst. and Pinus sylvestris L.) in both datasets and analyzed 909 records of the onset of wood formation at 47 sites and 238,720 records of budburst date at 3051 sites. We quantified chilling accumulation (CA) and forcing requirement (FR) of budburst and onset of wood formation based on common measures of CA and FR. We then constructed negative exponential CA–FR curves for bud and wood phenology separately. The results showed that the median, variance and probability distribution of CA–FR curves varied significantly between bud and wood phenology for three conifers. The different FR under the same chilling condition caused asynchronous bud and wood phenology. Furthermore, the CA–FR curves manifested that wood phenology was more sensitive to chilling than bud phenology. Thus, the FR of the onset of wood formation increases more than that of budburst under the same warming scenarios, explaining the stronger earlier trends in the budburst date than the onset date of woody formation simulated by the process-based model. Our work not only provides a possible explanation for asynchronous bud and wood phenology from the perspective of organ-specific responses to chilling and forcing, but also develops a phenological model for predicting both bud and wood phenology with acceptable uncertainties. [ABSTRACT FROM AUTHOR]

Shrub willows are widely planted for landscaping, soil remediation, and biomass production, due to their rapid growth rates. Identification of regulatory genes in wood formation would provide clues for genetic engineering of willows for improved growth traits on marginal lands. Here, we conducted an expression quantitative trait locus (eQTL) analysis, using a full sibling F1 population of Salix suchowensis, to explore the genetic mechanisms underlying wood formation. Based on variants identified from simplified genome sequencing and gene expression data from RNA sequencing, 16,487 eQTL blocks controlling 5505 genes were identified, including 2148 cis-eQTLs and 16,480 trans-eQTLs. eQTL hotspots were identified, based on eQTL frequency in genomic windows, revealing one hotspot controlling genes involved in wood formation regulation. Regulatory networks were further constructed, resulting in the identification of key regulatory genes, including three transcription factors (JAZ1, HAT22, MYB36) and CLV1, BAM1, CYCB2;4, CDKB2;1, associated with the proliferation and differentiation activity of cambium cells. The enrichment of genes in plant hormone pathways indicates their critical roles in the regulation of wood formation. Our analyses provide a significant groundwork for a comprehensive understanding of the regulatory network of wood formation in S. suchowensis. [ABSTRACT FROM AUTHOR]

European beech Fagus sylvatica and Sessile oak Quercus petraea are reaching the north-eastern limits of their natural ranges in northern Poland. According to the projected changes in potential ranges in this region, climatic conditions for both species until 2080 will remain stable. On the other hand, a decrease in the vitality of mature trees and a reduction in their radial growth are currently observed. To understand these contradictory findings, we monitored the cambial activity in both species during two vegetation seasons. 2015 was characterized by a negative water balance, while 2017 was wet. This provided an opportunity to compare how the xylogenesis proceeds in diffuse-porous beech and ring-porous oak during contrasting in the summer precipitation seasons. The forming annual increments were sampled with Presler borer at variable time intervals depending on the leaf phenological phases. The cores were prepared using a sledge microtome and double-stained with safranin and astra blue. Observations of the phases of wood formation and measurements of the width of the forming increments were analysed on the microslide digital images. Differences in the dates of the phenological phases were analysed using Two-Way ANOVA, while the dynamics of the formation of annual increments were fitted to the Single and Double Gompertz function for beech and oak, respectively. The beginning of vessel formation started earlier in both seasons compared to previous studies. Inter-seasonal differences in the duration of spring phenological phases were insignificant for both species, while inter-species differences were significant due to physiological diversity between diffuse-porous beech and ring-porous oak. In dry 2015, cambial activity ceased sooner in both species than in 2017. Differences between oak and beech were insignificant in both years, but statistically significant disparities existed within each species due to varying in precipitation seasons. Rainfall significantly elongated the duration of cambial activity and caused wider tree-rings. According to our study, despite predicted maintaining their climatic niche, both species, situated at the north-eastern cooler range boundary, are expected to produce wood at a lower rate due to the projected warmer central European climate with increased heatwaves and summer droughts. [ABSTRACT FROM AUTHOR]

Wood density is a crucial factor in determining the quality of wood in boreal ecosystems within the Northern Hemisphere. Climate variables play a significant role in shaping wood density, posing challenges for forest managers and stakeholders in the wood industry to adapt amidst climate change. However, our current understanding of these effects remains incomplete. This systematic literature review explores the multifaceted influences on wood density in the boreal zone, encompassing both climate-related and non-climatic factors. The findings demonstrate that warmer temperatures can cause both increases and decreases in wood density, primarily due to their impact on tracheid lignification and cell wall thickening. Nonetheless, the outcome depends on various factors, including species type, age, soil conditions, presence of pests and diseases, fire, windstorms, and silviculture practices. The quantification of complex relationships between these factors and wood density has been insufficient in existing literature. Understanding the impacts of both climate and non-climate factors on wood density is essential for fostering a sustainable wood industry, while effectively mitigating adverse effects and maximizing benefits. Forest managers can leverage this knowledge to optimize wood production strategies, ensuring long-term ecological resilience amidst the increasingly variable climate challenges. [ABSTRACT FROM AUTHOR]

Wood is the most important renewable resource not only for numerous practical utilizations but also for mitigating the global climate crisis by sequestering atmospheric carbon dioxide. The compressed wood (CW) of gymnosperms, such as conifers, plays a pivotal role in determining the structure of the tree through the reorientation of stems displaced by environmental forces and is characterized by a high content of lignin. Despite extensive studies on many genes involved in wood formation, the molecular mechanisms underlying seasonal and, particularly, CW formation remain unclear. This study examined the seasonal dynamics of two wood tissue types in Pinus densiflora: CW and opposite wood (OW). RNA sequencing of developing xylem for two consecutive years revealed comprehensive transcriptome changes and unique differences in CW and OW across seasons. During growth periods, such as spring and summer, we identified 2255 transcripts with differential expression in CW, with an upregulation in lignin biosynthesis genes and significant downregulation in stress response genes. Notably, among the laccases critical for monolignol polymerization, PdeLAC17 was found to be specifically expressed in CW, suggesting its vital role in CW formation. PdeERF4, an ERF transcription factor preferentially expressed in CW, seems to regulate PdeLAC17 activity. This research provides an initial insight into the transcriptional regulation of seasonal CW development in P. densiflora, forming a foundation for future studies to enhance our comprehension of wood formation in gymnosperms. [ABSTRACT FROM AUTHOR]

Summary: The kinetics of wood formation in angiosperms are largely unknown because their complex xylem anatomy precludes using the radial position of vessels and fibers to infer their time of differentiation.We analyzed xylogenesis in ring‐porous ash (Fraxinus angustifolia) and diffuse‐porous beech (Fagus sylvatica) over 1 yr and proposed a novel procedure to assess the period of vessel and fiber enlargement using a referential radial file (RRF).Our approach captured the dynamics of wood formation and provided a robust estimation of the kinetics of vessel and fiber enlargement. In beech, fibers and vessels had a similar duration of enlargement, decreasing from 14 to 5 d between April and July. In ash, wide vessels formed in April enlarged at a rate of 27 × 103 μm2 d−1, requiring half the time of contemporary fibers (6 vs 12 d), and less time than the narrower vessels (14 d) formed in May.These findings reveal distinct cell‐type‐dependent mechanisms for differentiation in diffuse‐porous and ring‐porous trees, enhancing our understanding of angiosperm wood cell kinetics. Our approach presents an effective method for investigating angiosperm wood formation and provides a more accurate representation of vessel and fiber morphogenesis in wood formation models. [ABSTRACT FROM AUTHOR]

Summary: The vascular cambium presents fundamental questions about the evolution and developmental biology of plants. Over time, our perspectives of the vascular cambium have changed as new molecular and genetic approaches have augmented anatomical observations and are now providing new insights into longstanding topics related to vascular cambium evolution, development and function. At the same time, practical applications of knowledge of the vascular cambium associated with climate change give new urgency to research of how the cambium produces varied wood anatomies both among species and within individual trees that influence response to drought and heat stress. Here, two topics are discussed that are generally related to the storied research of Sherwin Carlquist and his pursuits of the vascular cambium; the identity and function of cambium initials, and the plasticity of wood anatomical traits related to adaptive hydraulic traits. This short paper ends with a call for integrative research that could provide new insights into how trees respond to climate change that take advantage of the comparative wood anatomy framework so well-articulated by Carlquist. [ABSTRACT FROM AUTHOR]

The vascular cambium is an extensive and permanent secondary meristem with wood cells products of periclinal divisions commonly contributed to two directions and arranged in radial files of trees. Cambium activity is the origin of timber production. Taxodium ascendens Brongn is an exotic species in China, and its apical meristem and cambial activity are still elusive, resulting in a lack of understanding about its wood formation and improvement. We thus addressed this knowledge gap by studying Cambium activity. For studying, twigs from five 30-year-old healthy trees were collected between February-2017 and March-2018. Anatomy deciphered its apical meristem with a Cryptomeria–Abies type. The procambium appeared after leaf primordium and initially presented five lobes as observed transversely from a one-year-old shoot. The procambium under the apical differentiated into protophloem first and then protoxylem toward the inside. It means that protoxylem differentiated later than protophloem did. After dormancy, the vascular cambium began to be active, starting in early April 2017, which was later than shoot differentiation. On 25 July 2017, the cambial zone had 9–10 immature xylem cell layers. Both initiation and cessation of the xylem preceded that of the phloem. Until 10 October 2017, few immature elements were found, indicating the translation of cells from activity to dormancy. On 15 November 2017, the cambium contained 3–4 cells in radial rows, which demonstrated the dormancy of the cambium until next spring. Furthermore, immature xylem elements increased as cell layers in the cambium zone and cell fission increased. The growth pattern of T. ascendens revealed that cambial activity is highly seasonal and dependent on changes in abiotic conditions. Thus, the wood formation in the species will be significantly altered in a changing climatic pattern. These enhance our understanding of tree growth science, wood formation, wood structure, wood properties variation and wood improvement in tree breeding. [ABSTRACT FROM AUTHOR]

Forests, comprising 31% of the Earth's surface, play pivotal roles in regulating the carbon, water, and energy cycles. Despite being far less diverse than angiosperms, gymnosperms account for over 50% of the global woody biomass production. To sustain growth and development, gymnosperms have evolved the capacity to sense and respond to cyclical environmental signals, such as changes in photoperiod and seasonal temperature, which initiate growth (spring and summer) and dormancy (fall and winter). Cambium, the lateral meristem responsible for wood formation, is reactivated through a complex interplay among hormonal, genetic, and epigenetic factors. Temperature signals perceived in early spring induce the synthesis of several phytohormones, including auxins, cytokinins, and gibberellins, which in turn reactivate cambium cells. Additionally, microRNA-mediated genetic and epigenetic pathways modulate cambial function. As a result, the cambium becomes active during the summer, resulting in active secondary xylem (i.e., wood) production, and starts to become inactive in autumn. This review summarizes and discusses recent findings regarding the climatic, hormonal, genetic, and epigenetic regulation of wood formation in gymnosperm trees (i.e., conifers) in response to seasonal changes. [ABSTRACT FROM AUTHOR]

Tracheary elements (TEs), including vessels and tracheids, occur as a product of xylogenesis and are highly adapted for the transportation of water and solutes. Xylogenesis or wood formation encompasses various stages of cellular development, which requires stringent temporal and spatial regulation. To further complicate matters, TEs are polymorphous and associated with other complex tissues. These complexities have necessitated the development of in vitro culture systems that are capable of synchronously inducing TEs on demand. In this review, we cover the challenges associated with inducing TEs in vitro and how this has been overcome using mesophyll and callus culture systems in herbaceous plants, yielding transdifferentiation efficiencies of up to 76% and 90%, respectively. We postulate that when equipped with such information, a great opportunity exists to optimise these culture systems in commercially valuable woody genera that currently display lower efficiencies in the range of 15.8–65%. Although both the mesophyll and callus induction cultures have proven essential for uncovering the fundamental processes associated with secondary growth, the mesophyll-based systems have recently become much less prominent (2.8x) in the literature compared to the callus-based systems. This is largely due to ease of application of the callus system to other plant species, paving the way for applications ranging from fundamental research in economically valuable woody genera to the 3D-printing of biomaterial products in vitro. [ABSTRACT FROM AUTHOR]