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Immense land-cover changes in Iceland over the last millennium have encompassed birch (Betula pubescencs) woodland depletion and extensive soil erosion; few studies have focused on spatial distribution change of birch woodland in Iceland over centuries. The main objectives of this study were to (1) map the changes of birch woodland cover in [THORN]jorsardalur (14,000 ha) in southern Iceland, over a period of 350 years from late sixteenth to early twentieth century, and (2) explain the impact of socio-economic and natural forces on the woodland cover over three periods: 1587-1708, 1708-1880 and 1880-1938. We used a combined approach of historical reconstruction from diverse written archives, GIS-techniques and field work. About half of the [THORN]jorsardalur valley was covered by birch woodland in the late sixteenth century but over a period of 350 years 94 % of woodland had been depleted. The woodland was intensively used for firewood and charcoal making during the period with limited land management restriction. The main driving force for this development was socio-economic, where the form of ownership was a fundamental factor for the fate of the woodland. Harsh climate and volcanism further exacerbated the woodland during times when it had become fragmented and beyond its state of recovery.

Background Salt stress is one of the major environmental factors affecting plant growth and productivity. BRI1-EMS suppressor 1/brassinazole-resistant 1 ((BES1/BZR1) plays an important role in responding to abiotic stress in plants. Although the impacts of BES1/BZR1 on plant growth and resistance have been documented, the potential mechanisms are not fully elucidated in Betula platyphylla . This work contributes to the understanding of how BES1/BZR1 promotes stress tolerance in woody plants. Results Six BES1/BZR1 family members were identified from Betula platyphylla . Cis -element analysis showed that the promoters of six genes were rich in ABA-responsive element (ABRE), MYB and MBS cis -acting elements, which are reported to be involved in abiotic stress responses. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that BpBZR1-6 (BPChr10G06000) could be induced by salt stress, ABA and BRs. BpBZR1-6 was localized in the nucleus and had transactivation activity. Ectopic expression of BpBZR1-6 enhanced Arabidopsis tolerance and decreased abscisic acid (ABA) sensitivity under salt treatment. Specifically, the seed germination rate, root length, fresh weight and chlorophyll content were significantly higher in BpBZR1-6 -overexpressing (OE) transgenic plants than in wild-type (WT) plants after salt stress ( P  < 0.05). Additionally, BpBZR1-6 overexpression showed enhanced the reactive oxygen species (ROS) scavenging capability under salt stress, including increasing the activities of antioxidant enzyme, resulting in a decrease in O 2 − and H 2 O 2 accumulation, and reducing malondialdehyde (MDA) content. Meanwhile, the expression levels of six antioxidant enzyme genes were higher in OE plants than in WT plants after stress. Conclusion BpBZR1-6 overexpression enhanced the salt tolerance of transgenic plants by modulating antioxidant enzyme gene expression and ROS scavenging, which may provide underlying strategy for breeding of salt-tolerant plants.

Summary Forest pests and diseases pose serious threats to the sustainable development of forestry. Plants have developed effective resistance mechanisms through long‐term evolution. Jasmonic acid and terpenoids play important roles in the defence response of plants against insects. Here, we discovered a transcription factor of the WRKY IIa subgroup, BpWRKY6, which is located in the nucleus, and the overexpression of BpWRKY6 in birch (Betula platyphylla) can increase resistance to gypsy moths (Lymantria dispar). The selective feeding results indicated that the gypsy moth tends to feed more on wild‐type (WT) and mutant birch. The overexpression of BpWRKY6 decreased feeding, delayed development, inhibited CarE activity, and increased the activities of GST and CYP450 in gypsy moth larvae, whereas gypsy moth larvae that fed on the mutant birch presented the opposite trend. Further analysis revealed that BpWRKY6 directly binds to the promoters of jasmonic acid (JA) synthesis genes, including BpLOX15, BpAOC4, and BpAOS1, and the terpenoid synthesis gene BpCYP82G1, promoting their expression and increasing the contents of JA, 4,8,12‐trimethyltrideca‐1,3,7,11‐tetraene (TMTT) and total terpenoids, thus affecting birch resistance to insects. In addition, BpWRKY6 was phosphorylated as a substrate for BpMAPK6, suggesting that BpWRKY6 functions through the MAPK signalling pathway. In conclusion, this study further improves the understanding of the insect defence response mechanism of plants to achieve green pest control and provide insect‐resistant germplasm resources.

Betula L. (birch) is a genus of approx. 60 species, subspecies or varieties with a wide distribution in the northern hemisphere, of ecological and economic importance. A new classification of Betula has recently been proposed based on morphological characters. This classification differs somewhat from previously published molecular phylogenies, which may be due to factors such as convergent evolution, hybridization, incomplete taxon sampling or misidentification of samples. While chromosome counts have been made for many species, few have had their genome size measured. The aim of this study is to produce a new phylogenetic and genome size analysis of the genus. Internal transcribed spacer (ITS) regions of nuclear ribosomal DNA were sequenced for 76 Betula samples verified by taxonomic experts, representing approx. 60 taxa, of which approx. 24 taxa have not been included in previous phylogenetic analyses. A further 49 samples from other collections were also sequenced, and 108 ITS sequences were downloaded from GenBank. Phylogenetic trees were built for these sequences. The genome sizes of 103 accessions representing nearly all described species were estimated using flow cytometry. As expected for a gene tree of a genus where hybridization and allopolyploidy occur, the ITS tree shows clustering, but not resolved monophyly, for the morphological subgenera recently proposed. Most sections show some clustering, but species of the dwarf section Apterocaryon are unusually scattered. Betula corylifolia (subgenus Nipponobetula) unexpectedly clusters with species of subgenus Aspera Unexpected placements are also found for B. maximowicziana, B. bomiensis, B. nigra and B. grossa Biogeographical disjunctions were found within Betula between Europe and North America, and also disjunctions between North-east and South-west Asia. The 2C-values for Betula ranged from 0·88 to 5·33 pg, and polyploids are scattered widely throughout the ITS phylogeny. Species with large genomes tend to have narrow ranges. Betula grossa may have formed via allopolyploidization between parents in subgenus Betula and subgenus Aspera. Betula bomiensis may also be a wide allopolyploid. Betula corylifolia may be a parental species of allopolyploids in the subsection Chinenses Placements of B. maximowicziana, B. michauxii and B. nigra need further investigation. This analysis, in line with previous studies, suggests that section Apterocaryon is not monophyletic and thus dwarfism has evolved repeatedly in different lineages of Betula Polyploidization has occurred many times independently in the evolution of Betula.

The immigration of woody plants, especially Betula (tree birch), is examined in relation to geomorphological regions in a compilation of Late-glacial plant macrofossil records from Denmark. The immigration of trees led to a large ecological transformation of the landscape and had a major effect on the flora and fauna available to Palaeolithic people. We show that soil type was a controlling factor in the development of vegetation during the Alleroed and Younger Dryas periods. Following the first immigration of trees during the Alleroed period, woods became established in the eastern part of Denmark, where ice advances from the Baltic had deposited calcareous and clayey sediments. The western and northern parts of Denmark that are characterised by more sandy and non-calcareous sediments remained treeless throughout the whole Late-glacial period. Finds from the Bromme Culture are concentrated in the region which was wooded, suggesting that the regional variable environment allowed local adaptations using the diverse resources available.

Background Plant architecture, which is mostly determined by shoot branching, plays an important role in plant growth and development. Thus, it is essential to explore the regulatory molecular mechanism of branching patterns based on the economic and ecological importance. In our previous work, a multiple-branches birch mutant br was identified from 19 CINNAMOYL-COENZYME A REDUCTASE 1 ( CCR1 )-overexpressed transgenic lines, and the expression patterns of differentially expressed genes in br were analyzed. In this study, we further explored some other characteristics of br , including plant architecture, wood properties, photosynthetic characteristics, and IAA and Zeatin contents. Meanwhile, the T-DNA insertion sites caused by the insertion of exogenous BpCCR1 in br were identified to explain the causes of the mutation phenotypes. Results The mutant br exhibited slower growth, more abundant and weaker branches, and lower wood basic density and lignin content than BpCCR1 transgenic line (OE2) and wild type (WT). Compared to WT and OE2, br had high stomatal conductance (Gs), transpiration rate (Tr), but a low non-photochemical quenching coefficient (NPQ) and chlorophyll content. In addition, br displayed an equal IAA and Zeatin content ratio of main branches’ apical buds to lateral branches’ apical buds and high ratio of Zeatin to IAA content. Two T-DNA insertion sites caused by the insertion of exogenous BpCCR1 in br genome were found. On one site, chromosome 2 (Chr2), no known gene was detected on the flanking sequence. The other site was on Chr5, with an insertion of 388 bp T-DNA sequence, resulting in deletion of 107 bp 5′ untranslated region (UTR) and 264 bp coding sequence (CDS) on CORONATINE INSENSITIVE 1 ( BpCOII ). In comparison with OE2 and WT, BpCOI1 was down-regulated in br , and the sensitivity of br to Methyl Jasmonate (MeJA) was abnormal. Conclusions Plant architecture, wood properties, photosynthetic characteristics, and IAA and Zeatin contents in main and lateral branches’ apical buds changed in br over the study’s time period. One T-DNA insertion was identified on the first exon of BpCOI1 , which resulted in the reduction of BpCOI1 expression and abnormal perception to MeJA in br . These mutation phenotypes might be associated with a partial loss of BpCOI1 in birch.

Tree bark is a highly specialized array of tissues that plays important roles in plant protection and development. Bark tissues develop from two lateral meristems; the phellogen (cork cambium) produces the outermost stem–environment barrier called the periderm, while the vascular cambium contributes with phloem tissues. Although bark is diverse in terms of tissues, functions and species, it remains understudied at higher resolution. We dissected the stem of silver birch (Betula pendula) into eight major tissue types, and characterized these by a combined transcriptomics and metabolomics approach. We further analyzed the varying bark types within the Betulaceae family. The two meristems had a distinct contribution to the stem transcriptomic landscape. Furthermore, inter- and intraspecies analyses illustrated the unique molecular profile of the phellem. We identified multiple tissue-specific metabolic pathways, such as the mevalonate/betulin biosynthesis pathway, that displayed differential evolution within the Betulaceae. A detailed analysis of suberin and betulin biosynthesis pathways identified a set of underlying regulators and highlighted the important role of local, small-scale gene duplication events in the evolution of metabolic pathways. This work reveals the transcriptome and metabolic diversity among bark tissues and provides insights to its development and evolution, as well as its biotechnological applications.

Summary Long noncoding RNAs (lncRNAs) play an important role in abiotic stress tolerance. However, their function in conferring abiotic stress tolerance is still unclear. Herein, we characterized the function of a salt‐responsive nuclear lncRNA (BplncSIR1) from Betula platyphylla (birch). Birch plants overexpressing and knocking out for BplncSIR1 were generated. BplncSIR1 was found to improve salt tolerance by inducing antioxidant activity and stomatal closure, and also accelerate plant growth. Chromatin isolation by RNA purification (ChIRP) combined with RNA sequencing indicated that BplncSIR1 binds to the promoter of BpNAC2 (encoding NAC domain‐containing protein 2) to activate its expression. Plants overexpressing and knocking out for BpNAC2 were generated. Consistent with that of BplncSIR1, overexpression of BpNAC2 also accelerated plant growth and conferred salt tolerance. In addition, BpNAC2 binds to different cis‐acting elements, such as G‐box and ‘CCAAT’ sequences, to regulate the genes involved in salt tolerance, resulting in reduced ROS accumulation and decreased water loss rate by stomatal closure. Taken together, BplncSIR1 serves as the regulator of BpNAC2 to induce its expression in response to salt stress, and activated BpNAC2 accelerates plant growth and improves salt tolerance. Therefore, BplncSIR1 might be a candidate gene for molecular breeding to cultivate plants with both a high growth rate and improved salt tolerance.

Background Triterpenoids from birch ( Betula platyphylla Suk.) exert antitumor and anti-HIV activities. Due to the complexity of plant secondary metabolic pathways, triterpene compounds in plants is not always determined by a single gene; they may be controlled by polygene quantitative traits. Secondary metabolism related to terpenoids involves tissue specificity and localisation of key biosynthetic enzymes. Terpene synthesis is influenced by light, hormones and other signals, as well as upstream transcription factor regulation. Results Anchor Herein, we identified and characterised two birch MYB transcription factors (TFs) that regulate triterpenoid biosynthesis. BpMYB21 and BpMYB61 are R2R3 TFs that positively and negatively regulate responses to methyl-jasmonate (MeJA) and salicyclic acid (SA), respectively. Expression of BpMYB21 and BpMYB61 was elevated in leaves and stems more than roots during July/August in Harbin, China. BpMYB21 expression was increased by abscisic acid (ABA), MeJA, SA and gibberellins (GAs). BpMYB61 expression in leaves and BpMYB21 expression in stems was reduced by ABA, MeJA and SA, while GAs, ethylene, and injury increased BpMYB61 expression. BpMYB21 was localised in nuclei, while BpMYB61 was detected in cell membranes and nuclei. Promoters for both BpMYB21 (1302 bp) and BpMYB61 (850 bp) were active. BpMYB21 and BpMYB61 were ligated into pYES3, introduced into AnchorINVScl (yeast strain without exogenous genes), INVScl-pYES2-SSAnchorAnchor (transgenic yeast strain harbouring the SS gene from birch), and INVScl-pYES2-SE (transgenic yeast strain harbouring the SE gene from birch), and the squalene content was highest in AnchorINVScl-pYES-MYB21-SS (transgenic yeast strain harbouring SS and MYB21 genes) and INVScl-pYES3-MYB61 (transgenic yeast strain harbouring the MYB61 gene). In BpMYB21 transgenic birch key triterpenoid synthesis genes were up-regulated, and in BpMYB61 transgenic birch AnchorFPS (farnesyl pyrophosphate synthase) and SS (squalene synthase) were up-regulated, but HMGR (3-hydroxy-3-methylglutaryl coenzyme a reductase), BPWAnchor (lupeol synthase), SE (squalene epoxidase) and BPY (b-amyrin synthase) were down-regulated. Both BpMYB21 and BpMYB61 specifically activate SE and BPX (cycloartenol synthase synthesis) promoters. Conclusions These findings support further functional characterisation of R2R3-MYB genes, and illuminate the regulatory role of BpMYB21 and BpMYB61 in the synthesis of birch triterpenoids.

The effects of asynchrony in the phenology of spring-feeding insect-defoliators and their host plants on insects' fitness, as well as the importance of this effect for the population dynamics of outbreaking species of insects, is a widespread and well-documented phenomenon. However, the spreading of this phenomenon through the food chain, and especially those mechanisms operating this spreading, are still unclear. In this paper, we study the effect of seasonally declined leafquality (estimated in terms of phenolics and nitrogen content) on herbivore fitness, immune parameters and resistance against pathogen by using the silver birch Betula pendula-gypsy moth Lymantria dispar-nucleopolyhedrovirus as the tritrophic system. We show that a phenological mismatch induced by the delay in the emergence of gypsy moth larvae and following feeding on mature leaves has negative effects on the female pupal weight, on the rate of larval development and on the activity of phenoloxidase in the plasma of haemolymph. In addition, the larval susceptibility to exogenous nucleopolyhydrovirus infection as well as covert virus activation were both enhanced due to the phenological mismatch. The observed effects of phenological mismatch on insect-baculovirus interaction may partially explain the strong and fast fluctuations in the population dynamics of the gypsy moth that is often observed in the studied part of the defoliator area. This study also reveals some indirect mechanisms of effect related to host plant quality, which operate through the insect innate immune status and affect resistance to both exogenous and endogenous virus.