Oleoresin defenses in conifers: chemical diversity, terpene synthases and limitations of oleoresin defense under climate change

Pathogenicity and induced resistance in Larix kaempferi and Larix olgensis inoculated with Endoconidiophora fujiensis

With climate warming and economic globalization, insect-microbe assemblages are becoming increasingly responsible for various devastating forest diseases worldwide. Japanese larch (Larix kaempferi) is extensively cultivated in China because of its high survival rate, rapid maturation and robust mechanical properties. Endoconidiophora fujiensis, an ophiostomatoid fungus associated with Ips subelongatus, has been identified as a lethal pathogen of L. kaempferi in Japan. However, there is a dearth of research on the pathogenicity of E. fujiensis in larches in China. Therefore, we investigated the pathogenicity of E. fujiensis in introduced L. kaempferi and indigenous larch (Larix olgensis) trees and compared the induced resistance responses to the pathogen in both tree species in terms of physiology and gene expression. Five-year-old saplings and 25-year-old adult trees of L. olgensis and L. kaempferi were inoculated in parallel during the same growing season. Endoconidiophora fujiensis exhibited high pathogenicity in both larch species, but particularly in L. kaempferi compared with L. olgensis adult trees; adult L. olgensis was more resistant to E. fujiensis than adult L. kaempferi, which was reflected in higher accumulation of defensive monoterpenes, such as myrcene, 3-carene and limonene and the earlier induction of defense genes catalase (CAT) and pathogenesis-related protein 1 (PR1). This study contributes to our understanding of the interactions between bark beetle-associated ophiostomatoid fungi and host larches, from phenotypic responses to alterations in secondary metabolites via defense- and metabolism-related gene activation, providing a valuable foundation for the management of larch diseases and pests in the future.

Isoprenoid emissions from Schima superba and Cunninghamia lanceolata: Their responses to elevated temperature by two warming facilities

Isoprenoids (including isoprene (ISO) and monoterpenes (MTs)) are the majority of biogenic volatile organic compounds (BVOCs) which are important carbon-containing secondary metabolites biosynthesized by organisms, especially plant in terrestrial ecosystem. Results of the warming effects on isoprenoid emissions vary within species and warming facilities, and thus conclusions remain controversial. In this study, two typical subtropical tree species seedlings of Schima superba and Cunninghamia lanceolata were cultivated under three conditions, namely no warming (CK) and two warming facilities (with infrared radiators (IR) and heating wires (HW)) in open top chamber (OTC), and the isoprenoid emissions were measured with preconcentor-GC-MS system after warming for one, two and four months. The results showed that the isoprenoid emissions from S. superba and C. lanceolata exhibited uniformity in response to two warming facilities. IR and HW both stimulated isoprenoid emissions in two plants after one month of treatment, with increased ratios of 16.3 % and 72.5 % for S. superba, and 2.47 and 5.96 times for C. lanceolata. However, the emissions were suppressed after four months, with more pronounced effect for HW. The variation in isoprenoid emissions was primarily associated with the levels of Pn, Tr, monoterpene synthase (MTPS) activity. C. lanceolata predominantly released MTs (mainly α-pinene, α-terpene, γ-terpene, and limonene), with 39.7 % to 99.6 % of the total isoprenoid but ISO was only a very minor constituent. For S. superba, MTs constituted 24.7 % to 96.1 % of total isoprenoid. It is noteworthy that HW generated a greater disturbance to physiology activity in plants. Our study provided more comprehensive and more convincing support for integrating temperature-elevation experiments of different ecosystems and assessing response and adaptation of forest carbon cycle to global warming.

Pathophysiology and transcriptomic responses of Pinus armandii defenses to ophiostomatoid fungi

Pinus armandii Franch. is an ecologically and economically important evergreen tree species native to western China. Dendroctonus armandi Tsai and Li and pathogenic ophiostomatoid fungi pose substantial threats to P. armandii. With the interplay between species, the defense mechanisms of P. armandii have evolved to withstand external biotic stressors. However, the interactions between P. armandii and pathogenic ophiostomatoid fungal species/strains remain poorly understood. We aimed to analyze the pathophysiological and molecular changes in P. armandii following artificial inoculation with four ophiostomatoid species (Graphilbum parakesiyea, Leptographium qinlingense, Ophiostoma shennongense and Ophiostoma sp. 1). The study revealed that L. qinlingense produced the longest necrotic lesions, and G. parakesiyea produced the shortest. All strains induced monoterpenoid release, and monoterpene levels of P. armandii were positively correlated with fungal virulence (R2 = 0.93, P < 0.01). Co-inoculation of two dominant highly (L. qinlingense) and weakly virulent (O. shennongense) pathogens reduced the pathogenicity of the highly virulent fungi. Transcriptomic analysis of P. armandii (LQ: L. qinlingense treatments, QS: co-inoculation treatments and OS: O. shennongense treatments) showed that the expression pattern of differentially expressed genes (DEGs) between QS and OS was similar, but different from that of LQ. The DEGs (LQ vs QS) involved in flavonoid biosynthesis and phenylpropanoid biosynthesis were downregulated. Notably, compared with LQ, QS significantly decreased the expression of host defense-related genes. This study provides a valuable theoretical basis for managing infestations of D. armandi and associated ophiostomatoid fungi.

Terpenoids are involved in the expression of systemic-induced resistance in Austrian pine

Terpenoids are defense metabolites that are induced upon infection or wounding. However, their role in systemic-induced resistance (SIR) is not known. Here, we explored the role of terpenoids in this phenomenon at a very early stage in the interaction between Austrian pine and the tip blight and canker pathogen Diplodia pinea. We induced Austrian pine saplings by either wounding or inoculating the lower stems with D. pinea. The seedlings were then challenged after 12 h, 72 h, or 10 days with D. pinea on the stem 15 cm above the induction. Lesion lengths and terpenoids were quantified at both induction and challenge locations. Key terpenoids were assayed for antifungal activity in in vitro bioassays. SIR increased with time and was correlated with the inducibility of several compounds. α-Pinene and a cluster of β-pinene, limonene, benzaldehyde, dodecanol, and n-dodecyl acrylate were positively correlated with SIR and were fungistatic in vitro, while other compounds were negatively correlated with SIR and appeared to serve as a carbon source for D. pinea. This study shows that, overall, terpenoids are involved in SIR in this system, but their role is nuanced, depending on the type of induction and time of incubation. We hypothesize that some, such as α-pinene, could serve in SIR signaling.

Drought increases Norway spruce susceptibility to the Eurasian spruce bark beetle and its associated fungi

Drought affects the complex interactions between Norway spruce, the bark beetle Ips typographus and associated microorganisms. We investigated the interplay of tree water status, defense and carbohydrate reserves with the incidence of bark beetle attack and infection of associated fungi in mature spruce trees. We installed roofs to induce a 2-yr moderate drought in a managed spruce stand to examine a maximum of 10 roof and 10 control trees for resin flow (RF), predawn twig water potentials, terpene, phenolic and carbohydrate bark concentrations, and bark beetle borings in field bioassays before and after inoculation with Endoconidiophora polonica and Grosmannia penicillata. Drought-stressed trees showed more attacks and significantly longer fungal lesions than controls, but maintained terpene resin defenses at predrought levels. Reduced RF and lower mono- and diterpene, but not phenolic concentrations were linked with increased host selection. Bark beetle attack and fungi stimulated chemical defenses, yet G. penicillata reduced phenolic and carbohydrate contents. Chemical defenses did not decrease under mild, prolonged drought in our simulated small-scale biotic infestations. However, during natural mass attacks, reductions in carbon fixation under drought, in combination with fungal consumption of carbohydrates, may deplete tree defenses and facilitate colonization by I. typographus.

The role of Manganese in tree defenses against pests and pathogens

Manganese (Mn) deficiency is a widespread occurrence across different landscapes, including agricultural systems and managed forests, and causes interruptions in the normal metabolic functioning of plants. The microelement is well-characterized for its role in the oxygen-evolving complex in photosystem II and maintenance of photosynthetic structures. Mn is also required for a variety of enzymatic reactions in secondary metabolism, which play a crucial role in defense strategies for trees. Despite the strong relationship between Mn availability and the biosynthesis of defense-related compounds, there are few studies addressing how Mn deficiency can impact tree defense mechanisms and the ensuing ecological patterns and processes. Understanding this relationship and highlighting the potentially deleterious effects of Mn deficiency in trees can also inform silvicultural and management decisions to build more robust forests. In this review, we address this relationship, focusing on forest trees. We describe Mn availability in forest soils, characterize the known impacts of Mn deficiency in plant susceptibility, and discuss the relationship between Mn and defense-related compounds by secondary metabolite class. In our review, we find several lines of evidence that low Mn availability is linked with lowered or altered secondary metabolite activity. Additionally, we compile documented instances where Mn limitation has altered the defense capabilities of the host plant and propose potential ecological repercussions when studies are not available. Ultimately, this review aims to highlight the importance of untangling the effects of Mn limitation on the ecophysiology of plants, with a focus on forest trees in both managed and natural stands.

Transcriptome profiles reveal response mechanisms and key role of PsNAC1 in Pinus sylvestris var. mongolica to drought stress

BACKGROUND

Drought stress severely impedes plant growth, and only a limited number of species exhibit long-term resistance to such conditions. Pinus sylvestris var. mongolica, a dominant tree species in arid and semi-arid regions of China, exhibits strong drought resistance and plays a crucial role in the local ecosystem. However, the molecular mechanisms underlying this resistance remain poorly understood.

RESULTS

Here, we conducted transcriptome sequence and physiological indicators analysis of needle samples during drought treatment and rehydration stages. De-novo assembly yielded approximately 114,152 unigenes with an N50 length of 1,363 bp. We identified 6,506 differentially expressed genes (DEGs), with the majority being concentrated in the heavy drought stage (4,529 DEGs). Functional annotation revealed enrichment of drought-related GO terms such as response to water (GO:0009415: enriched 108 genes) and response to water deprivation (GO:0009414: enriched 106 genes), as well as KEGG categories including MAPK signaling pathway (K04733: enriched 35 genes) and monoterpenoid biosynthesis (K21374: enriched 27 genes). Multiple transcription factor families and functional protein families were differentially expressed during drought treatment. Co-expression network analysis identified a potential drought regulatory network between cytochrome P450 genes (Unigene4122_c1_g1) and a core regulatory transcription factor Unigene9098_c3_g1 (PsNAC1) with highly significant expression differences. We validated PsNAC1 overexpression in Arabidopsis and demonstrated enhanced drought resistance.

CONCLUSIONS

These findings provide insight into the molecular basis of drought resistance in P. sylvestris var. mongolica and lay the foundation for further exploration of its regulatory network.

Classification, biosynthesis, and biological functions of triterpene esters in plants

Triterpene esters comprise a class of secondary metabolites that are synthesized by decorating triterpene skeletons with a series of oxidation, glycosylation, and acylation modifications. Many triterpene esters with important bioactivities have been isolated and identified, including those with applications in the pesticide, pharmaceutical, and cosmetic industries. They also play essential roles in plant defense against pests, diseases, physical damage (as part of the cuticle), and regulation of root microorganisms. However, there has been no recent summary of the biosynthetic pathways and biological functions of plant triterpene esters. Here, we classify triterpene esters into five categories based on their skeletons and find that C-3 oxidation may have a significant effect on triterpenoid acylation. Fatty acid and aromatic moieties are common ligands present in triterpene esters. We further analyze triterpene ester synthesis-related acyltransferases (TEsACTs) in the triterpene biosynthetic pathway. Using an evolutionary classification of BAHD acyltransferases (BAHD-ATs) and serine carboxypeptidase-like acyltransferases (SCPL-ATs) in Arabidopsis thaliana and Oryza sativa, we classify 18 TEsACTs with identified functions from 11 species. All the triterpene-skeleton-related TEsACTs belong to BAHD-AT clades IIIa and I, and the only identified TEsACT from the SCPL-AT family belongs to the CP-I subfamily. This comprehensive review of the biosynthetic pathways and bioactivities of triterpene esters provides a foundation for further study of their bioactivities and applications in industry, agricultural production, and human health.

Alcohol dehydrogenases regulated by a MYB44 transcription factor underlie Lauraceae citral biosynthesis

Lineage-specific terpenoids have arisen throughout the evolution of land plants and are believed to play a role in interactions between plants and the environment. Species-specific gene clusters in plants have provided insight on the evolution of secondary metabolism. Lauraceae is an ecologically important plant family whose members are also of considerable economic value given their monoterpene contents. However, the gene cluster responsible for the biosynthesis of monoterpenes remains yet to be elucidated. Here, a Lauraceae-specific citral biosynthetic gene cluster (CGC) was identified and investigated using a multifaceted approach that combined phylogenetic, collinearity, and biochemical analyses. The CGC comprises MYB44 as a regulator and 2 alcohol dehydrogenases (ADHs) as modifying enzymes, which derived from species-specific tandem and proximal duplication events. Activity and substrate divergence of the ADHs has resulted in the fruit of mountain pepper (Litsea cubeba), a core Lauraceae species, consisting of more than 80% citral. In addition, MYB44 negatively regulates citral biosynthesis by directly binding to the promoters of the ADH-encoding genes. The aggregation of citral biosynthetic pathways suggests that they may form the basis of important characteristics that enhance adaptability. The findings of this study provide insights into the evolution of and the regulatory mechanisms involved in plant terpene biosynthesis.

The impact of insect egg deposition on Pinus sylvestris transcriptomic and phytohormonal responses to larval herbivory

Plants can improve their resistance to feeding damage by insects if they have perceived insect egg deposition prior to larval feeding. Molecular analyses of these egg-mediated defence mechanisms have until now focused on angiosperm species. It is unknown how the transcriptome of a gymnosperm species responds to insect eggs and subsequent larval feeding. Scots pine (Pinus sylvestris L.) is known to improve its defences against larvae of the herbivorous sawfly Diprion pini L. if it has previously received sawfly eggs. Here, we analysed the transcriptomic and phytohormonal responses of Scots pine needles to D. pini eggs (E-pine), larval feeding (F-pine) and to both eggs and larval feeding (EF-pine). Pine showed strong transcriptomic responses to sawfly eggs and-as expected-to larval feeding. Many egg-responsive genes were also differentially expressed in response to feeding damage, and these genes play an important role in biological processes related to cell wall modification, cell death and jasmonic acid signalling. EF-pine showed fewer transcriptomic changes than F-pine, whereas EF-treated angiosperm species studied so far showed more transcriptional changes to the initial phase of larval feeding than only feeding-damaged F-angiosperms. However, as with responses of EF-angiosperms, EF-pine showed higher salicylic acid concentrations than F-pine. Based on the considerable overlap of the transcriptomes of E- and F-pine, we suggest that the weaker transcriptomic response of EF-pine than F-pine to larval feeding damage is compensated by the strong, egg-induced response, which might result in maintained pine defences against larval feeding.

Plant secondary metabolites involved in the stress tolerance of long-lived trees

Ancient trees are natural wonders because of their longevity, having lived for hundreds or thousands of years, and their ability to withstand changing environments and a variety of stresses. These long-lived trees have sophisticated defense mechanisms, such as the production of specialized plant metabolites (SPMs). In this review, we provide an overview of the major biotic and abiotic stresses that long-lived trees often face, as well as an analysis of renowned ancient tree species and their unique protective SPMs against environmental stressors. We also discuss the synthesis and accumulation of defensive SPMs induced by environmental factors and endophytes in these trees. Furthermore, we conducted a comparative genomic analysis of 17 long-lived tree species and discovered significant expansions of SPM biosynthesis gene families in these species. Our comprehensive review reveals the crucial role of SPMs in high resistance in long-lived trees, providing a novel natural resource for plant defense, crop improvement and even the pharmaceutical industry.

A neutral theory of plant carbon allocation

How plants use the carbon they gain from photosynthesis remains a key area of study among plant ecologists. Although numerous theories have been presented throughout the years, the field lacks a clear null model. To fill this gap, I have developed the first null model, or neutral theory, of plant carbon allocation using probability theory, plant biochemistry and graph theory at the level of a leaf. Neutral theories have been used to establish a null hypothesis in molecular evolution and community assembly to describe how much of an ecological phenomenon can be described by chance alone. Here, the aim of a neutral theory of plant carbon allocation is to ask: how is carbon partitioned between sinks if one assumes plants do not prioritize certain sinks over others? Using the biochemical network of plant carbon metabolism, I show that, if allocation was strictly random, carbon is more likely to be allocated to storage, defense, respiration and finally growth. This 'neutral hierarchy' suggests that a sink's biochemical distance from photosynthesis plays an important role in carbon allocation patterns, highlighting the potentially adaptive role of this biochemical network for plant survival in variable environments. A brief simulation underscores that our ability to measure the carbon allocation from photosynthesis to a given sink is unreliable due to simple probabilistic rules. While neutral theory may not explain all patterns of carbon allocation, its utility is in the minimal assumptions and role as a null model against which future data should be tested.

Long-insert sequence capture detects high copy numbers in a defence-related beta-glucosidase gene βglu-1 with large variations in white spruce but not Norway spruce

Conifers are long-lived and slow-evolving, thus requiring effective defences against their fast-evolving insect natural enemies. The copy number variation (CNV) of two key acetophenone biosynthesis genes Ugt5/Ugt5b and βglu-1 may provide a plausible mechanism underlying the constitutively variable defence in white spruce (Picea glauca) against its primary defoliator, spruce budworm. This study develops a long-insert sequence capture probe set (Picea_hung_p1.0) for quantifying copy number of βglu-1-like, Ugt5-like genes and single-copy genes on 38 Norway spruce (Picea abies) and 40 P. glauca individuals from eight and nine provenances across Europe and North America respectively. We developed local assemblies (Piabi_c1.0 and Pigla_c.1.0), full-length transcriptomes (PIAB_v1 and PIGL_v1), and gene models to characterise the diversity of βglu-1 and Ugt5 genes. We observed very large copy numbers of βglu-1, with up to 381 copies in a single P. glauca individual. We observed among-provenance CNV of βglu-1 in P. glauca but not P. abies. Ugt5b was predominantly single-copy in both species. This study generates critical hypotheses for testing the emergence and mechanism of extreme CNV, the dosage effect on phenotype, and the varying copy number of genes with the same pathway. We demonstrate new approaches to overcome experimental challenges in genomic research in conifer defences.

Characterization of Larix decidua Mill. (Pinaceae) oleoresin's essential oils composition using GC-MS

Introduction

Larch oleoresin has been described regarding several biological activities and medicinal applications, such as wound healing and treatment of ulcers, but little is known about its chemical composition.

Material and methods

Eight oleoresins from Larix decidua Mill. obtained from four companies and one adulterated control were therefore investigated to determine their content of essential oils and to verify possible differences in their composition in relation to the harvest and manufacturing processes. Essential oils (EOs) were isolated by distillation and the yield was analysed.

Results and discussion

The yield of EO varied among all samples. The yield of the pure larch samples covered a range of 7.8% to 15.5%. A higher yield (19.0%) was observed for adulterated control, which contained oleoresins from different Pinaceae trees. Age of samples had no impact on yield. However, there was a significant statistical variation (p<0.05) in the yields of the mid-summer oleoresins (>10%) compared to early or late summer (<10%), emphasising the importance of the time of collection. Samples were subsequently analysed by GC-MS. EO samples confirmed the presence of various chemical classes, such as monoterpenes, sesquiterpenes, and diterpenes. α-pinene was the compound with the highest concentrations (>50%), followed by β-pinene (>6%), D-limonene (>2.5%), α-terpineol (>0.9%), β-myrcene (>0.2%), and 3-carene (>0.05%). Samples were grouped using multivariate data analysis (MVDA) with respect to the chemical variation between the oleoresins' EOs. The resulting four clusters were named low (low yield obtained for the samples), mixed (mixed oleoresin from different Pinaceae species, adulteration control), old (old oleoresin kept in the institute), and normal (other oleoresins) samples, each presenting distinct chemical biomarkers. There were considerable differences between site and time of collection. Essential oil yield did not always meet requirements as defined by the German Homeopathic Pharmacopoeia. In addition, adulterated or aged samples could be identified as compared to pure and fresh larch oleoresins.

Conclusion

We conclude that larch oleoresin used for pharmaceutical applications has to be carefully analysed and standardised to guarantee reproducible product quality.

Plant Engineering to Enable Platforms for Sustainable Bioproduction of Terpenoids

Terpenoids represent the most diverse class of natural products, with a broad spectrum of industrial relevance including applications in green solvents, flavors and fragrances, nutraceuticals, colorants, and therapeutics. They are typically challenging to extract from their natural sources, where they occur in small amounts and mixtures of related but unwanted byproducts. Formal chemical synthesis, where established, is reliant on petrochemistry. Hence, there is great interest in developing sustainable solutions to assemble biosynthetic pathways in engineered host organisms. Metabolic engineering for chemical production has largely focused on microbial hosts, yet plants offer a sustainable production platform. In addition to containing the precursor pathways that generate the terpenoid building blocks as well as the cell structures and compartments required, or tractable localization for the enzymes involved, plants may provide a low input system to produce these chemicals using carbon dioxide and sunlight only. There have been significant recent advancements in the discovery of pathways to terpenoids of interest as well as strategies to boost yields in host plants. While part of the phytochemical field is focusing on the discovery of biosynthetic pathways, this review will focus on advancements using the pathway toolbox and toward engineering plants for the production of terpenoids. We will highlight strategies currently used to produce target products, optimization of known pathways to improve yields, compartmentalization of pathways within cells, and genetic tools developed to facilitate complex engineering of biosynthetic pathways. These advancements in Synthetic Biology are bringing engineered plant systems closer to commercially relevant hosts for the bioproduction of terpenoids.

Assembly and annotation of the black spruce genome provide insights on spruce phylogeny and evolution of stress response

Black spruce (Picea mariana [Mill.] B.S.P.) is a dominant conifer species in the North American boreal forest that plays important ecological and economic roles. Here, we present the first genome assembly of P. mariana with a reconstructed genome size of 18.3 Gbp and NG50 scaffold length of 36.0 kbp. A total of 66,332 protein-coding sequences were predicted in silico and annotated based on sequence homology. We analyzed the evolutionary relationships between P. mariana and 5 other spruces for which complete nuclear and organelle genome sequences were available. The phylogenetic tree estimated from mitochondrial genome sequences agrees with biogeography; specifically, P. mariana was strongly supported as a sister lineage to P. glauca and 3 other taxa found in western North America, followed by the European Picea abies. We obtained mixed topologies with weaker statistical support in phylogenetic trees estimated from nuclear and chloroplast genome sequences, indicative of ancient reticulate evolution affecting these 2 genomes. Clustering of protein-coding sequences from the 6 Picea taxa and 2 Pinus species resulted in 34,776 orthogroups, 560 of which appeared to be specific to P. mariana. Analysis of these specific orthogroups and dN/dS analysis of positive selection signatures for 497 single-copy orthogroups identified gene functions mostly related to plant development and stress response. The P. mariana genome assembly and annotation provides a valuable resource for forest genetics research and applications in this broadly distributed species, especially in relation to climate adaptation.

Long term effects of ionising radiation in the Chernobyl Exclusion zone on DNA integrity and chemical defence systems of Scots pine (Pinus sylvestris)

The Chernobyl Nuclear Power Plant (ChNPP) accident in 1986 resulted in extremely high levels of acute ionising radiation, that killed or damaged Scots pine (Pinus sylvestris) trees in the surrounding areas. Dead trees were cleared and buried, and new plantations established a few years later. Today, more than three decades later, gamma and beta-radiation near the ChNPP is still elevated compared with ambient levels but have decreased by a factor of 300 and 100, respectively. In the present work, Scots pine-trees growing at High (220 μGy h-1), Medium (11 μGy h-1), and Low (0.2 μGy h-1) total (internal + external) dose rates of chronically elevated ionising radiation in the Chernobyl Exclusion zone were investigated with respect to possible damage to DNA, cells and organelles, as well as potentially increased levels of phenolic and terpenoid antioxidants. Scots pine from the High and Medium radiation sites had elevated levels of DNA damage in shoot tips and needles as shown by the COMET assay, as well as increased numbers of resin ducts and subcellular abnormalities in needles. Needles from the High radiation site showed elevated levels of monoterpenes and condensed tannins compared with those from the other sites. In conclusion, more than three decades after the ChNPP accident substantial DNA damage and (sub)cellular effects, but also mobilisation of stress-protective substances possessing antioxidant activity were observed in Scots pine trees growing at elevated levels of ionising radiation. This demonstrates that the radiation levels in the Red Forest still significantly impact the plant community.

Unraveling the terpene synthase family and characterization of BsTPS2 contributing to (S)-( +)-linalool biosynthesis in Boswellia

Boswellia tree bark exudes oleo-gum resin in response to wounding, which is rich in terpene volatiles. But, the molecular and biochemical basis of wound-induced formation of resin volatiles remains poorly understood. Here, we combined RNA-sequencing (RNA-seq) and metabolite analysis to unravel the terpene synthase (TPS) family contributing to wound-induced biosynthesis of resin volatiles in B. serrata, an economically-important Boswellia species. The analysis of large-scale RNA-seq data of bark and leaf samples representing more than 600 million sequencing reads led to the identification of 32 TPSs, which were classified based on phylogenetic relationship into various TPSs families found in angiosperm species such as TPS-a, b, c, e/f, and g. Moreover, RNA-seq analysis of bark samples collected at 0-24 h post-wounding shortlisted 14 BsTPSs that showed wound-induced transcriptional upregulation in bark, suggesting their important role in wound-induced biosynthesis of resin volatiles. Biochemical characterization of a bark preferentially-expressed and wound-inducible TPS (BsTPS2) in vitro and in planta assays revealed its involvement in resin terpene biosynthesis. Bacterially-expressed recombinant BsTPS2 catalyzed the conversion of GPP and FPP into (S)-( +)-linalool and (E)-(-)-nerolidol, respectively, in vitro assays. However, BsTPS2 expression in Nicotiana benthamiana found that BsTPS2 is a plastidial linalool synthase. In contrast, cytosolic expression of BsTPS2 did not form any product. Overall, the present work unraveled a suite of TPSs that potentially contributed to the biosynthesis of resin volatiles in Boswellia and biochemically characterized BsTPS2, which is involved in wound-induced biosynthesis of (S)-( +)-linalool, a monoterpene resin volatile with a known role in plant defense.

A Pine in Distress: How Infection by Different Pathogenic Fungi Affect Lodgepole Pine Chemical Defenses

In North America, lodgepole pine is frequently subjected to attacks by various biotic agents that compromise its ability to defend against subsequent attacks by insect herbivores. We investigated whether infections of lodgepole pine by different pathogenic fungal species have varying effects on its defense chemistry. We selected two common pathogens, Atropellis canker, Atropellis piniphila, and western gall rust, Endocronartium harknessii, affecting mature lodgepole pine trees in western Canada. We also included three ophiostomatoid fungi Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum associated with the mountain pine beetle (Dendroctonus ponderosae), because they are commonly used to investigate induced defenses of host trees of bark beetles. We collected phloem samples from lodgepole pines infected with the rust or the canker and healthy lodgepole pines in the same stand. We also inoculated mature lodgepole pines with the three fungal symbionts and collected phloem samples 2 weeks later when the defense chemistry was at its highest level. Different fungal species differentially altered the terpene chemistry of lodgepole pine trees. E. harknessii and the fungal symbionts altered the terpene chemistry in a similar pattern while trees responded to the infection by the A. piniphila differently. Our study highlights the importance of considering specific biotic stress agents in tree susceptibility or resistance to the subsequent attacks by insect herbivores, such as mountain pine beetle.

Rosin from Pinus pinaster Portuguese forests shows a regular profile of resin acids

Pinus pinaster forestry occupies >20% of the forest ecosystem area in the continental territory of Portugal with a high impact on the national economy. This species' major derived non-wood product is oleoresin, the raw material for rosin production. Rosin comprises mainly a blend of resin acids and has broad industrial and pharmaceutical applications. Oleoresin production in Portugal has been progressively reduced due to low-cost producers in other countries; currently, it reaches only 2% of the existing P. pinaster trees. To support this value chain, the chemical fingerprint of rosin derived from the national forest requires focused analysis. In the present study, we collected oleoresin within seven geographically distinct pure P. pinaster forests in two consecutive collection years. A high-resolution nuclear magnetic resonance (NMR) method was used to quantify the diversity of resin acids in the corresponding rosin samples. Overall, the acquired data highlighted that the profile of resin acids in P. pinaster rosin produced in Portugal is highly regular, regardless of the forest location, having as the major constituents abietic acid and dehydroabietic acid. The diversity of resin acids is possibly influenced, to a minor extent, by some edaphoclimatic factors.

Genome and transcriptome of Ips nitidus provide insights into high-altitude hypoxia adaptation and symbiosis

Ips nitidus is a well-known conifer pest that has contributed significantly to spruce forest disturbance in the Qinghai-Tibet Plateau and seriously threatens the ecological balance of these areas. We report a chromosome-level genome of I. nitidus determined by PacBio and Hi-C technology. Phylogenetic inference showed that it diverged from the common ancestor of I. typographus ∼2.27 mya. Gene family expansion in I. nitidus was characterized by DNA damage repair and energy metabolism, which may facilitate adaptation to high-altitude hypoxia. Interestingly, differential gene expression analysis revealed upregulated genes associated with high-altitude hypoxia adaptation and downregulated genes associated with detoxification after feeding and tunneling in fungal symbiont Ophiostoma bicolor-colonized substrates. Our findings provide evidence of the potential adaptability of I. nitidus to conifer host, high-altitude hypoxia and insight into how fungal symbiont assist in this process. This study enhances our understanding of insect adaptation, symbiosis, and pest management.

Volatile Organic Compounds from Cassava Plants Confer Resistance to the Whitefly Aleurothrixus aepim (Goeldi, 1886)

Cassava is an essential tuber crop used to produce food, feed, and beverages. Whitefly pests, including Aleurothrixus aepim (Goeldi, 1886) (Hemiptera: Aleyrodidae), significantly affect cassava-based agroecosystems. Plant odours have been described as potential pest management tools, and the cassava clone M Ecuador 72 has been used by breeders as an essential source of resistance. In this study, we analysed and compared the volatile compounds released by this resistant clone and a susceptible genotype, BRS Jari. Constitutive odours were collected from young plants and analysed using gas chromatography-mass spectrometry combined with chemometric tools. The resistant genotype released numerous compounds with previously described biological activity and substantial amounts of the monoterpene (E)-β-ocimene. Whiteflies showed non-preferential behaviour when exposed to volatiles from the resistant genotype but not the susceptible genotype. Furthermore, pure ocimene caused non-preferential behaviour in whiteflies, indicating a role for this compound in repellence. This report provides an example of the intraspecific variation in odour emissions from cassava plants alongside information on odorants that repel whiteflies; these data can be used to devise whitefly management strategies. A better understanding of the genetic variability in cassava odour constituents and emissions under field conditions may accelerate the development of more resistant cassava varieties.

Physiological, Proteomic, and Resin Yield-Related Genes Expression Analysis Provides Insights into the Mechanisms Regulating Resin Yield in Masson Pine

Masson pine (Pinus massoniana Lamb.) is an important resin-producing conifer species in China. Resin yield is a highly heritable trait and varies greatly among different genotypes. However, the mechanisms regulating the resin yield of masson pine remain largely unknown. In this study, physiological, proteomic, and gene expression analysis was performed on xylem tissues of masson pine with high and low resin yield. Physiological investigation showed that the activity of terpene synthase, as well as the contents of soluble sugar, jasmonic acid (JA), methyl jasmonate (MeJA), gibberellins (GA1, GA4, GA9, GA19, and GA20), indole-3-acetic acid (IAA), and abscisic acid (ABA) were significantly increased in the high yielder, whereas sucrose and salicylic acid (SA) were significantly decreased compared with the low one. A total of 2984 differentially expressed proteins (DEPs) were identified in four groups, which were mainly enriched in the biosynthesis of secondary metabolites, protein processing in the endoplasmic reticulum, carbohydrate metabolism, phytohormone biosynthesis, glutathione metabolism, and plant-pathogen interaction. Integrated physiological and proteomic analysis revealed that carbohydrate metabolism, terpenoid biosynthesis, resistance to stress, as well as JA and GA biosynthesis and signaling, play key roles in regulating resin yield. A series of proteins associated with resin yield, e.g., terpene synthase proteins (TPSs), ATP-binding cassette transporters (ABCs), glutathione S-transferase proteins (GSTs), and heat shock proteins (HSPs), were identified. Resin yield-related gene expression was also associated with resin yield. Our study unveils the implicated molecular mechanisms regulating resin yield and is of pivotal significance to breeding strategies of high resin-yielding masson pine cultivars.

Transcriptome features of stone cell development in weevil-resistant and susceptible Sitka spruce

Stone cells are a specialized, highly lignified cell type found in both angiosperms and gymnosperms. In conifers, abundance of stone cells in the cortex provides a robust constitutive physical defense against stem feeding insects. Stone cells are a major insect-resistance trait in Sitka spruce (Picea sitchensis), occurring in dense clusters in apical shoots of trees resistant (R) to spruce weevil (Pissodes strobi) but being rare in susceptible (S) trees. To learn more about molecular mechanisms of stone cell formation in conifers, we used laser microdissection and RNA sequencing to develop cell-type-specific transcriptomes of developing stone cells from R and S trees. Using light, immunohistochemical, and fluorescence microscopy, we also visualized the deposition of cellulose, xylan, and lignin associated with stone cell development. A total of 1293 genes were differentially expressed at higher levels in developing stone cells relative to cortical parenchyma. Genes with potential roles in stone cell secondary cell wall formation (SCW) were identified and their expression evaluated over a time course of stone cell formation in R and S trees. The expression of several transcriptional regulators was associated with stone cell formation, including a NAC family transcription factor and several genes annotated as MYB transcription factors with known roles in SCW formation.

Essential Oils for the Conservation of Paper Items

Archival documents and artworks stored in libraries frequently undergo degradative processes promoted by the so-called "biodeteriogens" that inhabit these places. A renewed interest in plant-derived products has arisen in those research groups focusing on cultural heritage preservation and looking for new and safe disinfection techniques. In this view, essential oils (EOs) and their volatile organic constituents are very appealing thanks to their versatility of action. A literature survey of the scientific publications involving EOs and/or their major constituents related to the conservation of paper items of cultural heritage interest is presented here, aiming to reveal benefits and limitations of such peculiar plant-derived compounds.

Cypress terpenes in sawfly larva of Susana cupressi (Hymenoptera: Symphyta: Tenthredinoidea)

Several sawfly species (Hymenoptera: Symphyta) possess larval stages with oesophageal diverticula in which plant compounds are sequestered and used for defence against predators. These organs are present in the larvae of Susana (Tenthredinidae) but remain poorly studied. Here, the aim was to analyse the diverticula extract of Susana cupressi by gas chromatography-mass spectrometry to better understand the ecology of this species. The foliage of the hostplant (Cupressus sempervirens), as well as the larval foregut, midgut, and haemolymph were also analysed. Complementary data were gathered by morphological observations, bioassays using ants, and genetic analyses to identify the studied Susana species. Altogether, 48 terpenes were identified, 30 being sesquiterpenes. The terpenes were generally detected in the foliage, but also in the diverticula, foregut, and midgut, whereas none of them in the haemolymph. The main compounds were alpha-cedrene, alpha-fenchene, alpha-pinene, alpha-terpinyl acetate, beta-myrcene, beta-pinene, cedrol, delta 3-carene, epi-bicyclosesquiphellandrene, germacrene D, limonene, sabinene, and terpinolene. The chemical profiles of these 13 compounds were significantly correlated between foliage-diverticula, diverticula-foregut and foregut-midgut, but not correlated for the three remaining possible comparisons. Alpha-pinene decreased and germacrene D increased from the foliage to the diverticula, which may reflect a specific sequestration of the latter terpene and its known deleterious effects on insects. We conclude that larvae of S. cupressi, similarly to those of diprionids, are well defended against predatory attacks by sequestering and regurgitating hostplant terpenes, including germacrene D.

Post-secretory synthesis of a natural analog of iron-gall ink in the black nectar of Melianthus spp

The black nectar produced by Melianthus flowers is thought to serve as a visual attractant to bird pollinators, but the chemical identity and synthesis of the black pigment are unknown. A combination of analytical biochemistry, transcriptomics, proteomics, and enzyme assays was used to identify the pigment that gives Melianthus nectar its black color and how it is synthesized. Visual modeling of pollinators was also used to infer a potential function of the black coloration. High concentrations of ellagic acid and iron give the nectar its dark black color, which can be recapitulated through synthetic solutions containing only ellagic acid and iron(iii). The nectar also contains a peroxidase that oxidizes gallic acid to form ellagic acid. In vitro reactions containing the nectar peroxidase, gallic acid, hydrogen peroxide, and iron(iii) fully recreate the black color of the nectar. Visual modeling indicates that the black color is highly conspicuous to avian pollinators within the context of the flower. Melianthus nectar contains a natural analog of iron-gall ink, which humans have used since at least medieval times. This pigment is derived from an ellagic acid-Fe complex synthesized in the nectar and is likely involved in the attraction of passerine pollinators endemic to southern Africa.

Functional characterization of a bark-specific monoterpene synthase potentially involved in wounding- and methyl jasmonate-induced linalool emission in rubber (Hevea brasiliensis)

Rubber (Hevea brasiliensis) is a latex-producing plant that often encounters mechanical wounding, as well as pathogen and pest attacks through wound sites during and after tapping. Terpenoids play an important role in the ecological interactions of many plant species, and their diversity is mainly generated by enzymes known as terpene synthases (TPS). In this study, one cDNA sequence encoding a putative terpene synthase, HbTPS20, was obtained from the bark tissues of H. brasiliensis. The encoded protein contains 610 amino acids with a putative N-terminal plastid transit peptide of approximately 70 residues. It belongs to the TPS-b subfamily. Further phylogenetic analysis showed that HbTPS20 formed a separate branch that diverged from the progenitor of all other potentially functional terpene synthases of the rubber TPS-b subfamily. The truncated HbTPS20 without the signal peptide coding sequence was successfully expressed in E. coli and in vitro enzymatic assays with geranyl diphosphate (GPP) or neryl diphosphate (NPP) as a substrate defined HbTPS20 as an active linalool synthase (HbLIS) with the ability to produce linalool as the principal product. RT-qPCR analysis showed that the highest transcript levels of HbTPS20 were found in barks, and this gene was expressed at 2.26- and 250-fold greater levels in the bark tissues of wounded and MeJA-treated plants, respectively, than in those of the control plants. This indicates that this gene may be involved in the induced stress responses of rubber.

Plant (di)terpenoid evolution: from pigments to hormones and beyond

Covering: up to 2014-2022.Diterpenoid biosynthesis in plants builds on the necessary production of (E,E,E)-geranylgeranyl diphosphate (GGPP) for photosynthetic pigment production, with diterpenoid biosynthesis arising very early in land plant evolution, enabling stockpiling of the extensive arsenal of (di)terpenoid natural products currently observed in this kingdom. This review will build upon that previously published in the Annual Review of Plant Biology, with a stronger focus on enzyme structure-function relationships, as well as additional insights into the evolution of (di)terpenoid metabolism since generated.

Phylotranscriptomics and evolution of key genes for terpene biosynthesis in Pinaceae

Pinaceae is the largest family of conifers, dominating forest ecosystems and serving as the backbone of northern, temperate and mountain forests. The terpenoid metabolism of conifers is responsive to pests, diseases, and environmental stress. Determining the phylogeny and evolution of terpene synthase genes in Pinaceae may shed light on early adaptive evolution. We used different inference methods and datasets to reconstruct the Pinaceae phylogeny based on our assembled transcriptomes. We identified the final species tree of Pinaceae by comparing and summarizing different phylogenetic trees. The genes encoding terpene synthase (TPS) and cytochrome P450 proteins in Pinaceae showed a trend of expansion compared with those in Cycas. Gene family analysis revealed that the number of TPS genes decreased while the number of P450 genes increased in loblolly pine. Expression profiles showed that TPSs and P450s were mainly expressed in leaf buds and needles, which may be the result of long-term evolution to protect these two vulnerable tissues. Our research provides insights into the phylogeny and evolution of terpene synthase genes in Pinaceae and offers some useful references for the investigation of terpenoids in conifers.

Genetic architecture of terpene chemistry and growth traits and the impact of inbreeding on these traits in western redcedar ( Thuja plicata )

Western redcedar (WRC; Thuja plicata) is a conifer of the Pacific Northwest of North America prized for its durable and rot-resistant wood. WRC has naturally low outcrossing rates and readily self-fertilizes in nature. Challenges faced in WRC breeding and propagation involve selecting trees for accelerated growth while also ensuring enhanced heartwood rot resistance and resistance to ungulate browsing, as well as mitigating potential effects of inbreeding depression. Terpenes, a large and diverse class of specialized metabolites, confer both rot and browse resistance in the wood and foliage of WRC, respectively. Using a Bayesian modelling approach, we isolated single nucleotide polymorphism (SNP) markers estimated to be associated with three different foliar terpene traits and four different heartwood terpene traits, as well as two growth traits. We found that all traits were complex, being associated with between 1700 and 3600 SNPs linked with putatively causal loci, with significant polygenic components. Growth traits tended to have a larger polygenic component while terpene traits had larger major gene components; SNPs with small or polygenic effect were spread across the genome, while larger-effect SNPs tended to be localized to specific linkage groups. To determine whether there was inbreeding depression for terpene chemistry or growth traits, we used mixed linear models for a genomic selection training population to estimate the effect of the inbreeding coefficient F on foliar terpenes, heartwood terpenes and several growth and dendrochronological traits. We did not find significant inbreeding depression for any assessed trait. We further assessed inbreeding depression across four generations of complete selfing and found that not only was inbreeding depression not significant but that selection for height growth was the only significant predictor for growth during selfing, suggesting that inbreeding depression due to selfing during operational breeding can be mitigated by increased selection intensity.

Detoxification of monoterpenes by a family of plant glycosyltransferases

Plant monoterpenes are challenging compounds, since they often act as solvents, and thus have both phytotoxic and antimicrobial properties. In this study an approach is developed to identify and characterize enzymes that can detoxify monoterpenoids, and thus would protect both plants and microbial production systems from these compounds. Plants respond to the presence of monoterpenes by expressing glycosyltransferases (UGTs), which conjugate the monoterpenoids into glycosides. By identifying these enzymes in a transcriptomics approach using Mentha × piperita, a family of UGTs was identified which is active on cyclic monoterpenoids such as menthol, and on acyclic monoterpenoids such as geranic acid. Other members of this family, from tomato, were also shown to be active on these monoterpenoids. In vitro and in vivo activity of different UGTs were tested with different substrates. We found that some glycosyltransferases significantly affect the toxicity of selected monoterpenoids in Escherichia coli, suggesting that glycosyltransferases can protect cells from monoterpenoid toxicity.

Sirex noctilio infestation led to inevitable pine death despite activating pathways involved in tolerance

Defense-related metabolome traits in pine species after infestation by Sirex noctilio are largely unknown, despite, in most cases, trees being overwhelmed. Using LC-MS-based untargeted metabolomics, we revealed the systemic metabolic changes induced by this insect in 14-year-old Pinus radiata trees, the most affected species worldwide. An immediate metabolome alteration was expressed in needles after infestation, including the up-regulation of flavonols, flavan-3-ols, oxyneolignans, auxins, proline, and tryptophan, among others. The flavan-3-ols (catechin and procyanidin B1) suggested a rapidly induced photoprotection mechanism aided by diverting proline as an alternative substrate for respiration to compensate for the progressive chlorosis that degrades photosystems. Meanwhile, glutathione, glutamate, and ascorbate levels significantly dropped in needles, which may indicate the critical oxidative stress that trees had to face since the onset of the infestation. They were not fully replenished after long-term infestation, and redox homeostasis was probably not achieved, compromising tree survival. Nevertheless, a huge auxins overexpression detected in needles throughout the infestation may reflect tolerance against the premature senescence caused by the woodwasp venom. In contrast, the metabolome of wood tissues remained initially unchanged, although it seems to collapse after three months. Overall, the metabolomics strategy adopted in this work evidenced its usefulness in uncovering the fundamental roles of plants' chemical defense that govern interactions with specific stressors.

Age-dependent modulation of oleoresin production in the stem of Sindora glabra

Plants produce specialized metabolites in various organs which serve important functions in defense and development. However, the molecular regulatory mechanisms of oleoresin production in stems from broadleaved tree species are not fully understood. To determine whether endogenous developmental cues play a role in the regulation of oleoresin biosynthesis in tree stems, anatomy, multi-omics and molecular experiments were utilized to investigate the change of secretory structures, chemical profiles and gene expression in different ontogenetic stages of Sindora glabra tree, which accumulates copious amount of sesquiterpene-rich oleoresin in stems. The size of secretory canals and the concentration of five sesquiterpenes in Sindora stems exhibited obvious increase with plant age, from 0.5- to 20-year-old plants. Moreover, α-copaene and β-copaene were found to be stem-specific sesquiterpenes. Metabolomic analysis revealed that salicylic acid highly accumulated in mature stems, but the content of triterpenes was greatly decreased. The expression of three repressors AUX/IAA, DELLA and JAZ involved in hormone signaling transduction pathways was significantly downregulated in stems of 10- and 20-year-old plants. Two key genes SgTPS3 and SgTPS5 were identified, whose expression was highly correlated with the accumulation patterns of specific sesquiterpenes and their enzymatic products were consistent with the chemical profiles in the stem. The promoters of three SgTPSs exhibiting high activity were isolated. Furthermore, we demonstrated that SgSPL15 directly interacts with SgTPS3 and SgTPS5 promoters and activates SgTPS5 expression but SgSPL15 inhibits SgTPS3 expression. In addition, SgSPL15 enhanced sesquiterpene levels by upregulating AtTPSs expression in Arabidopsis. These results suggested that sesquiterpene biosynthesis in S. glabra stem was dependent on the regulation of endogenous hormones as well as plant age, and SgSPL15 might act as a buffering factor to regulate sesquiterpene biosynthesis by targeting SgTPS genes.

Identification of Genes and Metabolic Pathways Involved in Resin Yield in Masson Pine by Integrative Analysis of Transcriptome, Proteome and Biochemical Characteristics

Masson pine (Pinus massoniana L.) is one of the most important resin-producing tree species in southern China. However, the molecular regulatory mechanisms of resin yield are still unclear in masson pine. In this study, an integrated analysis of transcriptome, proteome, and biochemical characteristics from needles of masson pine with the high and common resin yield was investigated. The results showed that chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl C), carotenoids (Car), glucose (Glu), gibberellin A9 (GA9), gibberellin A15 (GA15), and gibberellin A53 (GA53) were significantly increased, whereas fructose (Fru), jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-ILE), gibberellin A1 (GA1), gibberellin A3 (GA3), gibberellin A19 (GA19), and gibberellin A24 (GA24) were significantly decreased in the high resin yield in comparison with those in the common one. The integrated analysis of transcriptome and proteome showed that chlorophyll synthase (chlG), hexokinase (HXK), sucrose synthase (SUS), phosphoglycerate kinase (PGK), dihydrolipoamide dehydrogenase (PDH), dihydrolipoamide succinyltransferase (DLST), 12-oxophytodienoic acid reductase (OPR), and jasmonate O-methyltransferases (JMT) were consistent at the transcriptomic, proteomic, and biochemical levels. The pathways of carbohydrate metabolism, terpenoid biosynthesis, photosynthesis, and hormone biosynthesis may play crucial roles in the regulation of resin yield, and some key genes involved in these pathways may be candidates that influence the resin yield. These results provide insights into the molecular regulatory mechanisms of resin yield and also provide candidate genes that can be applied for the molecular-assisted selection and breeding of high resin-yielding masson pine.

Volatile-mediated between-plant communication in Scots pine and the effects of elevated ozone

Conifers are dominant tree species in boreal forests, but are susceptible to attack by bark beetles. Upon bark beetle attack, conifers release substantial quantities of volatile organic compounds known as herbivore-induced plant volatiles (HIPVs). Earlier studies of broadleaved plants have shown that HIPVs provide information to neighbouring plants, which may enhance their defences. However, the defence responses of HIPV-receiver plants have not been described for conifers. Here we advance knowledge of plant-plant communication in conifers by documenting a suite of receiver-plant responses to bark-feeding-induced volatiles. Scots pine seedlings exposed to HIPVs were more resistant to subsequent weevil feeding and received less damage. Receiver plants had both induced and primed volatile emissions and their resin ducts had an increased epithelial cell (EC) mean area and an increased number of cells located in the second EC layer. Importantly, HIPV exposure increased stomatal conductance and net photosynthesis rate of receiver plants. Receiver-plant responses were also examined under elevated ozone conditions and found to be significantly altered. However, the final defence outcome was not affected. These findings demonstrate that HIPVs modulate conifer metabolism through responses spanning photosynthesis and chemical defence. The responses are adjusted under ozone stress, but the defence benefits remain intact.

The mechanisms and prediction of non-structural carbohydrates accretion and depletion after mechanical wounding in slash pine (Pinus elliottii) using near-infrared reflectance spectroscopy

BACKGROUND

The allocation of non-structural carbohydrates (NSCs) plays a critical role in the physiology and metabolism of tree growth and survival defense. However, little is known about the allocation of NSC after continuous mechanical wounding of pine by resin tapping during tree growth.

RESULTS

Here, we examine the NSC allocation in plant tissues after 3 year lasting resin tapping, and also investigate the use of near-infrared reflectance (NIR) spectroscopy to quantify the NSC, starch and free sugar (e.g., sucrose, glucose, and fructose) concentrations in different plant tissues of slash pine. Spectral measurements on pine needle, branch, trunk phloem, and root were obtained before starch and free sugar concentrations were measured in the laboratory. The variation of NSC, starch and free sugars in different plant tissues after resin tapping was analyzed. Partial least squares regression was applied to calibrate prediction models, models were simulated 100 times for model performance and error estimation. More NSC, starch and free sugars were stored in winter than summer both in tapped and control trees. The position of resin tapping significantly influenced the NSCs allocation in plant tissues: more NSCs were transformed into free sugars for defensive resin synthesis close to the tapping wound rather than induced distal systemic responses. Models for predicting NSC and free sugars of plant tissues showed promising results for the whole tree for fructose (R²_CV = 0.72), glucose (R²_CV = 0.67), NSCs (R²_CV = 0.66) and starch (R²_CV = 0.58) estimates based on NIR models. Models for individual plant tissues also showed reasonable predictive ability: the best model for NSCs and starch prediction was found in root. The significance multivariate correlation algorithm for variable selection significantly reduced the number of variables. Important variables were identified, including features at 1021-1290 nm, 1480, 1748, 1941, 2020, 2123 and 2355 nm, which are highly related to NSC, starch, fructose, glucose and sucrose.

CONCLUSIONS

NIR spectroscopy provided a rapid and cost-effective method to monitor NSC, starch and free sugar concentrations after continuous resin tapping. It can be used for studying the trade-off between growth and production of defensive metabolites.

Chromosome-level genome assembly and population genomic analyses provide insights into adaptive evolution of the red turpentine beetle, Dendroctonus valens

BACKGROUND

Biological invasions are responsible for substantial environmental and economic losses. The red turpentine beetle (RTB), Dendroctonus valens LeConte, is an important invasive bark beetle from North America that has caused substantial tree mortality in China. The lack of a high-quality reference genome seriously limits deciphering the extent to which genetic adaptions resulted in a secondary pest becoming so destructive in its invaded area.

RESULTS

Here, we present a 322.41 Mb chromosome-scale reference genome of RTB, of which 98% of assembled sequences are anchored onto fourteen linkage groups including the X chromosome with a N50 size of 24.36 Mb, which is significantly greater than other Coleoptera species. Repetitive sequences make up 45.22% of the genome, which is higher than four other Coleoptera species, i.e., Mountain pine beetle Dendroctonus ponderosae, red flour beetle Tribolium castaneum, blister beetle Hycleus cichorii, and Colorado potato beetle Leptinotarsa decemlineata. We identify rapidly expanded gene families and positively selected genes in RTB, which may be responsible for its rapid environmental adaptation. Population genetic structure of RTB was revealed by genome resequencing of geographic populations in native and invaded regions, suggesting substantial divergence of the North American population and illustrates the possible invasion and spread route in China. Selective sweep analysis highlighted the enhanced ability of Chinese populations in environmental adaptation.

CONCLUSIONS

Overall, our high-quality reference genome represents an important resource for genomics study of invasive bark beetles, which will facilitate the functional study and decipher mechanism underlying invasion success of RTB by integrating the Pinus tabuliformis genome.

Constitutive and Induced Defenses in Long-lived Pines Do Not Trade Off but Are Influenced by Climate

Plants resist herbivores and pathogens by using constitutive (baseline) and inducible (change in defense after an attack) defenses. Inducibility has long been predicted to trade off with constitutive defense, reflecting the economic use of resources. However, empirical evidence for such tradeoffs is variable, and we still lack understanding about when and where defense trade-offs occur. We tested for tradeoffs between constitutive and induced defenses in natural populations of three species of long-lived pines (Pinus balfouriana, P. flexilis, P. longaeva) that differ greatly in constitutive defense and resistance to mountain pine beetle (MPB, Dendroctonus ponderosae). We also assessed how climate influenced constitutive and inducible defenses. At seven high-elevation sites in the western U.S., we simulated MPB attack to induce defenses and measured concentrations of terpene-based phloem defenses on days 0, 15, and 30. Constitutive and induced defenses did not trade off among or within species. Simulated MPB attack induced large increases in defense concentrations in all species independent of constitutive levels. MPB and its symbiotic fungi typically kill trees and thus could be selective forces maintaining strong inducibility within and among species. The contrasting constitutive concentrations in these species could be driven by the adaptation for specializing in harsh, high-elevation environments (e.g., P. balfouriana and P. longaeva) or by competition (e.g., P. flexilis), though these hypotheses have not been empirically examined. Climate influenced defenses, with the greatest concentrations of constitutive and induced defenses occurring at the coldest and driest sites. The interactions between climate and defenses have implications for these species under climate change.

Effects of elevated ozone and warming on terpenoid emissions and concentrations of Norway spruce depend on needle phenology and age

Norway spruce (Picea abies (L.) Karst) trees are affected by ongoing climate change, including warming and exposure to phytotoxic levels of ozone. Non-volatile terpenoids and volatile terpenoids (biogenic organic volatile compounds, BVOCs) protect spruce against biotic and abiotic stresses. BVOCs also affect the atmosphere's oxidative capacity. Four-year-old Norway spruce were exposed to elevated ozone (EO) (1.4 × ambient) and warming (1.1 °C + ambient air) alone and in combination on an open-field exposure site in Central Finland. Net photosynthesis, needle terpenoid concentrations and BVOC emissions were measured four times during the experiment's second growing season: after bud opening in May, during the mid-growing season in June, and after needle maturation in August and September. Warming increased terpene concentrations in May due to advanced phenology and decreased them at the end of the growing season in matured current-year needles. Ozone enhanced these effects of warming on several compounds. Warming decreased concentrations of oxygenated sesquiterpenes in previous-year needles. Decreased emissions of oxygenated monoterpenes by warming and ozone alone in May were less prominent when ozone and warming were combined. A similar interactive treatment response in isoprene, camphene, tricyclene and α-pinene was observed in August when the temperature and ozone concentration was high. The results suggest long-term warming may reduce the terpenoid-based defence capacity of young spruce, but the defence capacity can be increased during the most sensitive growth phase (after bud break), and when high temperatures or ozone concentrations co-occur. Reduced BVOC emissions from young spruce may decrease the atmosphere's oxidative capacity in the warmer future, but the effect of EO may be marginal because less reactive minor compounds are affected.

Pathophysiology and transcriptomic analysis of Picea koraiensis inoculated by bark beetle-vectored fungus Ophiostoma bicolor

Ophiostomatoid fungi exhibit a complex relationship with bark beetles; exhausting of host tree defenses is traditionally regarded as one of the key benefits provided to beetle vectors. Ophiostoma bicolor is one of the dominant species of the mycobiota associated with Ips genus bark beetles which infect the spruce trees across the Eurasian continent. Host spruce trees resist fungal invasion through structural and inducible defenses, but the underlying mechanisms at the molecular level, particularly with respect to the interaction between bark beetle-associated fungi and host trees, remain unclear. The aim of this study was to observe the pathological physiology and molecular changes in Picea koraiensis seedlings after artificial inoculation with O. bicolor strains (TS, BH, QH, MX, and LWQ). This study showed that O. bicolor was a weakly virulent pathogen of spruce, and that the virulent of the five O. bicolor strains showed differentiation. All O. bicolor strains could induce monoterpenoid release. A positive correlation between fungal virulence and release of monoterpenoids was observed. Furthermore, the release rate of monoterpenoids peaked at 4 days post-inoculation (dpi) and then decreased from 4 to 90 dpi. Transcriptomic analysis at 4 dpi showed that many plant-pathogen interaction processes and mitogen-activated protein kinase (MAPK) metabolic processes were activated. The expression of monoterpenoid precursor synthesis genes and diterpenoid synthesis genes was upregulated, indicating that gene expression regulated the release rate of monoterpenoids at 4 dpi. The enriched pathways may reveal the immune response mechanism of spruce to ophiostomatoid fungi. The dominant O. bicolor possibly induces the host defense rather than defense depletion, which is likely the pattern conducted by the pioneers of beetle-associated mycobiota, such as Endoconidiophora spp.. Overall, these results facilitate a better understanding of the interaction mechanism between the dominant association of beetles and the host at the molecular level.

Analysis of Transcriptome and Terpene Constituents of Scots Pine Genotypes Inherently Resistant or Susceptible to Heterobasidion annosum

Root and stem rot caused by Heterobasidion annosum is a severe problem in boreal Scots pine. Dissecting the features of disease resistance is generally an essential step in resistance breeding in plants and forest trees. In this study, we explored inherent resistance factors of Scots pine against H. annosum. A total of 236 families consisting of 85 full-sib (FS), 35 half-sib population mix (HSpm), and 116 half-sib (HS) families of Scots pine seedlings were inoculated with a H. annosum isolate. We sampled needle tissues before inoculation for terpene measurements and RNA sequencing. Based on the lesion area, the extremes of 12 resistant and 12 susceptible families were selected for further analyses. Necrotic lesions resulting from fungal infection were in a weak to moderate relationship with the plant height. Monoterpenes were the principal terpene compounds observed in Scots pine seedlings. Concentrations of 3-carene were significantly higher in pine genotypes inherently resistant compared with susceptible seedlings. By contrast, susceptible genotypes had significantly higher proportions of α-pinene. Gene ontology analysis of differential expressed transcripts (DETs) revealed that response to biotic factors was enriched in resistant seedlings. Functional characterization of individual DETs revealed that higher expression of transcripts involved in response to abiotic stress was common in susceptible genotypes. This observation was supported by the annotation of hub genes in a key module that was significantly correlated with the lesion trait through weighted gene co-expression network analysis (WGCNA) of 16 HS and HSpm samples. These findings contribute to our understanding of constitutive resistance factors of Scots pine against Heterobasidion root and stem rot diseases.

Identification and Defensive Characterization of PmCYP720B11v2 from Pinus massoniana

Pinus massoniana is a pioneer species for afforestation timber and oleoresin, while epidemics of pinewood nematode (PWN; Bursaphelenchus xylophilus) are causing a serious biotic disaster for P. massoniana in China. Importantly, resistant P. massoniana could leak copious oleoresin terpenoids to build particular defense fronts for survival when attacked by PWN. However, the defense mechanisms regulating this process remain unknown. Here, PmCYP720B11v2, a cytochrome P450 monooxygenase gene, was first identified and functionally characterized from resistant P. massoniana following PWN inoculation. The tissue-specific expression pattern and localization of PmCYP720B11v2 at the transcript and protein levels in resistant P. massoniana indicated that its upregulation in the stem supported its involvement in the metabolic processes of diterpene biosynthesis as a positive part of the defense against PWN attack. Furthermore, overexpression of PmCYP720B11v2 may enhance the growth and development of plants. In addition, PmCYP720B11v2 activated the metabolic flux of antioxidases and stress-responsive proteins under drought conditions and improved drought stress tolerance. Our results provide new insights into the favorable role of PmCYP720B11v2 in diterpene defense mechanisms in response to PWN attack in resistant P. massoniana and provide a novel metabolic engineering scenario to reform the stress tolerance potential of tobacco.

Transcriptomic changes during the establishment of long-term methyl jasmonate-induced resistance in Norway spruce

Norway spruce (Picea abies) is an economically and ecologically important tree species that grows across northern and central Europe. Treating Norway spruce with jasmonate has long-lasting beneficial effects on tree resistance to damaging pests, such as the European spruce bark beetle Ips typographus and its fungal associates. The (epi)genetic mechanisms involved in such long-lasting jasmonate induced resistance (IR) have gained much recent interest but remain largely unknown. In this study, we treated 2-year-old spruce seedlings with methyl jasmonate (MeJA) and challenged them with the I. typographus vectored necrotrophic fungus Grosmannia penicillata. MeJA treatment reduced the extent of necrotic lesions in the bark 8 weeks after infection and thus elicited long-term IR against the fungus. The transcriptional response of spruce bark to MeJA treatment was analysed over a 4-week time course using mRNA-seq. This analysis provided evidence that MeJA treatment induced a transient upregulation of jasmonic acid, salicylic acid and ethylene biosynthesis genes and downstream signalling genes. Our data also suggests that defence-related genes are induced while genes related to growth are repressed by methyl jasmonate treatment. These results provide new clues about the potential underpinning mechanisms and costs associated with long-term MeJA-IR in Norway spruce.

Expression and promoter analysis of MEP pathway enzyme-encoding genes in Pinus massoniana Lamb

The methylerythritol phosphate (MEP) pathway provides the universal basic blocks for the biosynthesis of terpenoids and plays a critical role in the growth and development of higher plants. Pinus massoniana is the most valuable oleoresin producer tree with an extensive terrestrial range. It has the potential to produce more oleoresin with commercial value, while being resistant to pine wood nematode (PWN) disease. For this study, eleven MEP pathway associated enzyme-encoding genes and ten promoters were isolated from P. massoniana. Three PmDXS and two PmHDR existed as multi-copy genes, whereas the other six genes existed as single copies. All eleven of these MEP enzymes exhibited chloroplast localization with transient expression. Most of the MEP genes showed higher expression in the needles, while PmDXS2, PmDXS3, and PmHDR1 had high expression in the roots. The expressions of a few MEP genes could be induced under exogenous elicitor conditions. The functional complementation in a dxs-mutant Escherichia coli strain showed the DXS enzymatic activities of the three PmDXSs. High throughput TAIL PCR was employed to obtain the upstream sequences of the genes encoding for enzymes in the MEP pathway, whereby abundant light responsive cis-elements and transcription factor (TF) binding sites were identified within the ten promoters. This study provides a theoretical basis for research on the functionality and transcriptional regulation of MEP enzymes, as well as a potential strategy for high-resin generation and improved genetic resistance in P. massoniana.

Prediction and Comparisons of Turpentine Content in Slash Pine at Different Slope Positions Using Near-Infrared Spectroscopy

Pine resin is one of the best known and most exploited non-wood products. Resin is a complex mixture of terpenes produced by specialized cells that are dedicated to tree defense. Chemical defenses are plastic properties, and concentrations of chemical defenses can be adjusted based on environmental factors, such as resource availability. The slope orientation (south/sunny or north/shady) and the altitude of the plantation site have significant effects on the soil nutrient and the plant performance, whereas little is known about how the slope affects the pine resin yield and its components. In total, 1180 slash pines in 18 plots at different slope positions were established to determine the effects on the α- and β-pinene content and resin production of the slash pine. The near-infrared spectroscopy (NIR) technique was developed to rapidly and economically predict the turpentine content for each sample. The results showed that the best partial least squares regression (PLS) models for α- and β-pinene content prediction were established via the combined treatment of multiplicative scatter correction–significant multivariate correlation (MSC–sMC). The prediction models based on sMC spectra for α- and β-pinene content have an R² of 0.82 and 0.85 and an RMSE of 0.96 and 0.82, respectively, and they were successfully implemented in turpentine prediction in this research. The results also showed that a barren slope position (especially mid-slope) could improve the α-pinene and β-pinene content and resin productivity of slash pine, and the β-pinene content in the resin had more variances in this research.

Integrating genomic information and productivity and climate-adaptability traits into a regional white spruce breeding program

Tree improvement programs often focus on improving productivity-related traits; however, under present climate change scenarios, climate change-related (adaptive) traits should also be incorporated into such programs. Therefore, quantifying the genetic variation and correlations among productivity and adaptability traits, and the importance of genotype by environment interactions, including defense compounds involved in biotic and abiotic resistance, is essential for selecting parents for the production of resilient and sustainable forests. Here, we estimated quantitative genetic parameters for 15 growth, wood quality, drought resilience, and monoterpene traits for Picea glauca (Moench) Voss (white spruce). We sampled 1,540 trees from three open-pollinated progeny trials, genotyped with 467,224 SNP markers using genotyping-by-sequencing (GBS). We used the pedigree and SNP information to calculate, respectively, the average numerator and genomic relationship matrices, and univariate and multivariate individual-tree models to obtain estimates of (co)variance components. With few site-specific exceptions, all traits examined were under genetic control. Overall, higher heritability estimates were derived from the genomic- than their counterpart pedigree-based relationship matrix. Selection for height, generally, improved diameter and water use efficiency, but decreased wood density, microfibril angle, and drought resistance. Genome-based correlations between traits reaffirmed the pedigree-based correlations for most trait pairs. High and positive genetic correlations between sites were observed (average 0.68), except for those pairs involving the highest elevation, warmer, and moister site, specifically for growth and microfibril angle. These results illustrate the advantage of using genomic information jointly with productivity and adaptability traits, and defense compounds to enhance tree breeding selection for changing climate.

The chromosome-scale genomes of Dipterocarpus turbinatus and Hopea hainanensis (Dipterocarpaceae) provide insights into fragrant oleoresin biosynthesis and hardwood formation

Dipterocarpaceae are typical tropical plants (dipterocarp forests) that are famous for their high economic value because of their production of fragrant oleoresins, top-quality timber and usage in traditional Chinese medicine. Currently, the lack of Dipterocarpaceae genomes has been a limiting factor to decipher the fragrant oleoresin biosynthesis and gain evolutionary insights into high-quality wood formation in Dipterocarpaceae. We generated chromosome-level genome assemblies for two representative Dipterocarpaceae species viz. Dipterocarpus turbinatus Gaertn. f. and Hopea hainanensis Merr. et Chun. Our whole-genome duplication (WGD) analysis revealed that Dipterocarpaceae underwent a shared WGD event, which showed significant impacts on increased copy numbers of genes related to the biosynthesis of terpene, BAHD acyltransferases, fatty acid and benzenoid/phenylpropanoid, which probably confer to the formation of their characteristic fragrant oleoresin. Additionally, compared with common soft wood plants, the expansion of gene families was also found to be associated with wood formation, such as in CESA (cellulose synthase), CSLE (cellulose synthase-like protein E), laccase and peroxidase in Dipterocarpaceae genomes, which might also contribute to the formation of harder, stronger and high-density timbers. Finally, an integrative analysis on a combination of genomic, transcriptomic and metabolic data from different tissues provided further insights into the molecular basis of fragrant oleoresins biosynthesis and high-quality wood formation of Dipterocarpaceae. Our study contributes the first two representative genomes for Dipterocarpaceae, which are valuable genetic resources for further researches on the fragrant oleoresins and superior-quality timber, genome-assisted breeding and improvement, and conservation biology of this family.