Lignin Pathway Research Articles

Slurry co-hydroprocessing of Kraft lignin and pyrolysis oil over unsupported NiMoS catalyst: A strategy for char suppression

Pyrolysis oil (PO) assisted Kraft lignin (KL) liquefaction over an unsupported NiMoS catalyst in a paraffin solvent was explored in this work. A paraffin solvent was used to represent hydrogenated vegetable oil (HVO) which is a biofuel. We have for the first time showed that when co-processing Kraft lignin with pyrolysis oil in a paraffin solvent the char formation could be completely suppressed. The complex composition of PO, containing various compounds with different functional groups, was able to aid the depolymerization pathways of lignin by obstructing the condensation path of reactive lignin derivatives. To further understand the role of different functional groups present in pyrolysis oil during lignin liquefaction, we investigate the co-hydroprocessing of Kraft lignin with various oxygenate monomers using unsupported NiMoS. 4-propylguaiacol (PG) was found to be the most efficient monomer for stabilizing the reactive lignin intermediates, resulting in a low char yield (3.7%), which was 4 times lower than the char production from Kraft lignin hydrotreatment alone. The suppressed rate of lignin fragment repolymerization can be attributed to the synergistic effect of functional groups like hydroxyl (-OH), methoxy (-OCH3), and propyl (-C3H7) groups present in PG. These groups were found to be able to stabilize the lignin depolymerized fragments and blocked the repolymerization routes enabling efficient lignin depolymerization. It was found that the presence of a co-reactant like PG during the heating period of the reactor acted as a blocking agent facilitating further depolymerization routes. Finally, a reaction network is proposed describing multiple routes of lignin hydroconversion to solid char, lignin-derived monomers, dimers, and oligomers, explaining why the co-processing of pyrolysis oil and Kraft lignin completely suppressed the solid char formation.

CRISPR/Cas9 mutated p-coumaroyl shikimate 3'-hydroxylase 3 gene in Populus tomentosa reveals lignin functioning on supporting tree upright

The lignin plays one of the most important roles in plant secondary metabolism. However, it is still unclear how lignin can contribute to the impressive height of wood growth. In this study, C3’H, a rate-limiting enzyme of the lignin pathway, was used as the target gene. C3’H3 was knocked out by CRISPR/Cas9 in Populus tomentosa. Compared with wild-type popular trees, c3’h3 mutants exhibited dwarf phenotypes, collapsed xylem vessels, weakened phloem thickening, decreased hydraulic conductivity and photosynthetic efficiency, and reduced auxin content, except for reduced total lignin content and significantly increased H-subunit lignin. In the c3’h3 mutant, the flavonoid biosynthesis genes CHS, CHI, F3H, DFR, ANR, and LAR were upregulated, and flavonoid metabolite accumulations were detected, indicating that decreasing the lignin biosynthesis pathway enhanced flavonoid metabolic flux. Furthermore, flavonoid metabolites, such as naringenin and hesperetin, were largely increased, while higher hesperetin content suppressed plant cell division. Thus, studying the c3’h3 mutant allows us to deduce that lignin deficiency suppresses tree growth and leads to the dwarf phenotype due to collapsed xylem and thickened phloem, limiting material exchanges and transport.

Integrative analysis of metabolome and transcriptome reveals the different metabolite biosynthesis profiles related to palatability in winter and spring shoot in moso bamboo

Moso bamboo winter shoot has good taste and rich nutritional value. To reveal the causes and regulatory mechanism of palatability deterioration from winter to spring shoot, a conjoint analysis of metabolome and transcriptome was conducted on winter and spring shoots of moso bamboo. Totally 909 metabolites were characterized for the first time. The significant increase of hydrolyzed tannin content intensified the bitterness of spring shoot, which was positively regulated by key metabolite (gallic acid) and genes (DAHPS, DHQS, DHQ, SDH) in the biosynthesis pathway of hydrolyzed tannin. The accumulation of lignified components enhanced the roughness of spring shoot, which was closely connected with the significant changes of important metabolites (cinnamic acid, ferulic acid, UDP-glucose and UDP-xylose) and up-regulation of most enzyme genes involved in the biosynthesis pathways of lignin, cellulose and hemicellulose. The present study provides theoretical support for understanding palatability transition and directional improvement of edible quality of moso bamboo shoots.

The key physiological and molecular responses of Neolamarckia cadamba to phosphorus deficiency stress by hydroponics

Phosphorus (P) is one of the most essential mineral elements and macronutrients required for plant growth and development, and its deficiency can affect the physiological and transcriptomic levels of plants, especially in acidic soils. Neolamarckia cadamba (N. cadamba) is a fast-growing tree species widely distributed in tropics and subtropics with acidic soils. However, the physiological and molecular responses of N. cadamba to phosphorus deficiency (PD) have not been well explored. Here, the responses of N. cadamba to PD stress were studied in hydroponic solution. PD stress reduced plant height, leaf size and biomass as well as photosynthetic capacity, but promoted root growth. Stem thickening of secondary xylem and lignification were promoted under PD stress. Meanwhile, the contents of P, Mg and Fe were significantly reduced, while those of Ca and Al were increased. Interestingly, antioxidant enzymes (e.g., POD, MDA, and CAT) were increased by PD stress, especially after 3 weeks. Transcriptome analysis showed that P uptake and transport-related genes PHT, PHO, PT, PAP, SPX, etc. were up-regulated in the root and stem of N. cadamba under PD stress. However, some genes involved in cation transporter and photosystem as well as chlorophyll proteins were down-regulated. Notably, genes associated with the lignin pathway and encoding reactive oxygen species (ROS) enzymes as well as transcription factors (mostly comprising MYB, bZIP, AP2, and HD-ZIP) were mainly up-regulated. Our findings provide new insights into the complex physiological and molecular mechanisms of the PD response in N. cadamba.

Foliar Application of Chitosan Accelerates Wound Periderm Formation with an Intensified Deposition of Suberin Polyphenolic and Lignin in the Wounds of Potato Tubers

Potato tubers are susceptible to wounding during post-harvest processes, leading to quality decline, perishability and large economic losses. In this study, the potato cultivar, ‘Longshu No.7′, was foliar-sprayed with 3% chitosan (w/v) three times during the pre-harvest period after flowering to evaluate the effect of foliar spraying with chitosan on suberization processing in the wounds of harvested potato tubers. Our results demonstrated that foliar sprayed with chitosan significantly reduced wound-induced fresh weight loss and dry rot disease index by 37.34% and 41.60% on day 28 after wounding, respectively. Foliar sprayed with chitosan accelerated the deposition of suberin polyphenolic and lignin at the wound sites of potato tubers with the formation of thicker cell layers. This occurred with increased localized activities of key enzymes in the suberin polyphenolic and lignin pathways, including phenylalanine ammonia lyase, 4-coumaryl-coenzyme A ligase, cinnamyl alcohol dehydrogenase and peroxidase (33.90–64.32%), as well as the contents of cinnamic acid, sinapic acid, flavonoids, lignins and total phenolics (19.70–23.46%) in the wounded sites of potato tubers on day 7 after wounding. Our results indicated that foliar application of chitosan accelerated wound-induced suberization of potato tubers and could mitigate post-harvest product damages.

Study on the mechanisms of hydrogen production from alkali lignin gasification in supercritical water by ReaxFF molecular dynamics simulation

Lignin is a major polymer in the black liquor of paper mill and one of the most important components of biomass. Supercritical water gasification (SCWG) technology, which is an efficient and clean method for waste lignin treatment, has a good application prospect. To improve the conversion efficiency of lignin, it is necessary to reveal the detail mechanisms of lignin gasification in supercritical water (SCW). Based on the actual molecular structure of lignin, a model of complex lignin was constructed by using Materials Studio (MS). The effects of different reaction parameters on gasification results were analyzed with the reactive force field molecular dynamics method (ReaxFF MD). The simulation results show that higher reaction temperature and lower reactant concentration lead to higher efficiency of lignin gasification in SCW, and lignin has the highest gasification efficiency at 3500 K and 15 wt%. Additionally, the decomposition pathway of lignin and the generation paths of CO2, H2 were clarified. This work will provide theoretical guidance for further research to improve the SCWG efficiency of lignin.

Cell wall remodeling in woody tung oil tree root xylem contributes to deterrence of the Fusarium wilt pathogen

Tung oil tree (Vernicia fordii), is renowned for production of unique tung oil, which has been suffered Fusarium wilt disease. Intriguingly, its sister species, woody tung oil trees (V. montana) exhibit high resistance to Fusarium. oxysporum f. sp. fordii (Fof-1) infection. We hypothesize that the xylem cells of V. montana roots might act as physical barriers to deter invasion of the soil-borne Fusarium pathogen. To test this, we investigated the potentially different phenotypic and physiological behaviors of the root xylem cells between V. montana and V. fordii responding to Fof-1. The result showed that pathogen could invade the root xylem of V. fordii but failed to enter the root xylem of V. montana. After Fof-1 infection, the cell wall thickness in V. montana root xylem was statistically increased. A statistically significant increase of lignin in the early stage, and the ratio of S:H lignin and hemicellulose content in the later infection stage were viewed in the V. montana root xylem cell wall. Further comparative metabolomic analysis showed that some intermediary metabolites in the lignin pathways, including cinnamic acid, scopoletin and coumarin, were enriched in V. montana root xylem cells after Fof-1 infection. Consistent with this, in V. montana, KEGG enrichment result also support the evidence that the upregulated genes were enriched in this pathway. The hub genes of lignin biosynthesis pathway in V. montana were further selected and verified using qRT-PCR. Together, our data demonstrated that the remodeling of cell wall in V. montana root xylem make primary contributions to decrease the Fof-1 infection. Promisingly, the discovery offers an opportunity to explore an effective strategy for breeding Fusarium resistant tung oil trees.

Transcriptional networks orchestrating red and pink testa color in peanut

BackgroundTesta color is an important trait of peanut (Arachis hypogaea L.) which is closely related with the nutritional and commercial value. Pink and red are main color of peanut testa. However, the genetic mechanism of testa color regulation in peanut is not fully understood. To elucidate a clear picture of peanut testa regulatory model, samples of pink cultivar (Y9102), red cultivar (ZH12), and two RNA pools (bulk red and bulk pink) constructed from F4 lines of Y9102 x ZH12 were compared through a bulk RNA-seq approach.ResultsA total of 2992 differential expressed genes (DEGs) were identified among which 317 and 1334 were up-regulated and 225 and 1116 were down-regulated in the bulk red-vs-bulk pink RNA pools and Y9102-vs-ZH12, respectively. KEGG analysis indicates that these genes were divided into significantly enriched metabolic pathways including phenylpropanoid, flavonoid/anthocyanin, isoflavonoid and lignin biosynthetic pathways. Notably, the expression of the anthocyanin upstream regulatory genes PAL, CHS, and CHI was upregulated in pink and red testa peanuts, indicating that their regulation may occur before to the advent of testa pigmentation. However, the differential expression of down-stream regulatory genes including F3H, DFR, and ANS revealed that deepening of testa color not only depends on their gene expression bias, but also linked with FLS inhibition. In addition, the down-regulation of HCT, IFS, HID, 7-IOMT, and I2’H genes provided an alternative mechanism for promoting anthocyanin accumulation via perturbation of lignin and isoflavone pathways. Furthermore, the co-expression module of MYB, bHLH, and WRKY transcription factors also suggested a fascinating transcriptional activation complex, where MYB-bHLH could utilize WRKY as a co-option during the testa color regulation by augmenting anthocyanin biosynthesis in peanut.ConclusionsThese findings reveal candidate functional genes and potential strategies for the manipulation of anthocyanin biosynthesis to improve peanut varieties with desirable testa color.

Lignin and Its Pathway-Associated Phytoalexins Modulate Plant Defense against Fungi.

Fungi infections cause approximately 60-70% yield loss through diseases such as rice blast, powdery mildew, Fusarium rot, downy mildew, etc. Plants naturally respond to these infections by eliciting an array of protective metabolites to confer physical or chemical protection. Among plant metabolites, lignin, a phenolic compound, thickens the middle lamella and the secondary cell walls of plants to curtail fungi infection. The biosynthesis of monolignols (lignin monomers) is regulated by genes whose transcript abundance significantly improves plant defense against fungi. The catalytic activities of lignin biosynthetic enzymes also contribute to the accumulation of other defense compounds. Recent advances focus on modifying the lignin pathway to enhance plant growth and defense against pathogens. This review presents an overview of monolignol regulatory genes and their contributions to fungi immunity, as reported over the last five years. This review expands the frontiers in lignin pathway engineering to enhance plant defense.

Activation of the phenylpropanoid pathway in Citrus sinensis collapsed vesicles during segment drying revealed by physicochemical and targeted metabolomics analysis

Segment drying is a common internal physiological disorder in citrus fruit, and vesicles get granulated or collapsed. This study aimed to probe whether and how the phenylpropanoid metabolism changes in vesicles during collapse of blood orange (Citrus sinensis cv. Tarocco). Vesicle collapse led to a decrease in the content of nutrients and flavonoids, while an increase in lignin content. This disorder was further associated with the increasing enzyme activities and gene expression levels of both the general phenylpropanoid pathway and branch pathway of lignin synthesis, while decreasing enzyme activities and gene expression levels of branch pathway of flavonoids synthesis. Targeted metabolomics analysis of 14 metabolites of the lignin pathway revealed that lignin precursors were accumulated in collapsed vesicles. We provide solid evidence that phenylpropanoid metabolism could be activated, and, intriguingly, metabolic flux may be shuttled to lignin precursors synthesis rather than flavonoids synthesis in vesicles during collapse of blood orange.

Cumulative exergy analysis of lignocellulosic biomass to bio-jet fuel through aqueous-phase conversion with different lignin conversion pathways

Lignocellulosic biomass conversion to bio-jet fuel is beneficial for reducing the depletion of fossil fuel. This study presented and compared the two different pathways of lignin in corn stalk to bio-jet fuel via aqueous-phase conversion based on the process simulation approach and life cycle cumulative exergy analysis. The results show that the pathway of lignin one-step conversion (LJA) can obtain a higher bio-jet fuel yield and cumulative exergy efficiency than lignin two-step conversion (LJC). Moreover, biomass conversion to bio-jet fuel with self-supplied hydrogen is beneficial to the conversion of low-quality biomass into high-quality bio-jet fuel and the decrease in fossil fuel consumption. Under the optimal parameters, corn stalk aqueous-phase conversion to bio-jet fuel with external-supplied hydrogen can achieve the largest bio-jet fuel yield (142.7 kg/t-bio) and cumulative exergy efficiency of system (29.3%). The sensitivity analyses show that the hydrolysis efficiency of lignin has the most influence on the cumulative exergy efficiency of bio-jet fuel, while the furfural yield from hemicellulose has the lowest impact. When the consumption of chemicals and steam is considered, it is significant to reduce the stripping steam to furfural ratio for the cumulative exergy efficiency and reduce the consumption of methanol and sulfuric acid for the renewability.

Physcomitrium patens CAD1 has distinct roles in growth and resistance to biotic stress

BackgroundPhyscomitrium patens provides an evolutionary link between green algae and vascular plants. Although the genome of P. patens includes orthologs of all the core lignin biosynthetic enzymes, the occurrence of lignin in moss is very controversial. Besides, little information is available about the lignin enzymes in moss to date. For example, cinnamyl alcohol dehydrogenase (CAD) is a crucial enzyme that catalyzes the last step of the lignin biosynthetic pathway, suggesting an ideal way to study the evolutionary process. By investigating the functions of CAD in evolution, this study will elucidate the evolutionary roles of lignin-like in the early stage of land colonization.ResultsCAD multigene family in P. patens is composed of four genes. The PpCADs contain a conserved glycine-rich domain to catalyze NADPH-dependent reduction to their corresponding alcohols, indicating that PpCADs have the potential to synthesize monolignols by bioinformatics analysis. Even though PpCAD1 could produce lignin in theory, no conventional monomer was detected in the cell wall or cytoplasm of PpCAD1_OE plants. However, the phenylpropanoids were promoted in PpCAD1_OE transformants to modify gametophore architecture and development, making the distribution of phyllids more scarcity and the moss colony more giant, possibly due to the enhanced expression of the AUX-IAA family. The transcripts of at least one gene encoding the enzyme in the lignin biosynthetic pathway were increased in PpCAD1_OE plants. In addition, the PpCAD1_OE gametophore inhibited the Botrytis cinerea assault mainly by enhanced phenylpropanoids in the cell wall instead of influencing transcripts of defense genes pathogenesis-related 10 (PR10) and nonexpresser of PR genes 1 (NPR1). Likewise, ectopic expression of PpCAD1 in Arabidopsis led to a significant increase in lignin content, exhibiting chunky roots, robust seedlings, advanced flowering, and efficient resistance against pathogens.ConclusionPpCAD occurs in more than one copy, suggesting functional divergence in the ancestral plant. PpCAD1 catalyzes monolignol biosynthesis and has homologous functions with vascular plants. Despite no detected conventional monolignol, the increased phenylpropanoids in the PpCAD1_OE gametophore, possibly intermediate metabolites in the lignin pathway, had conserved functions during the evolution of terrestrial plants. The results inferred that the lignin enzyme of the early non-vascular plant played roles in stem elongation and resistance against pathogens of P. patens during the conquest of land.

Transcriptome and metabolome analyses reveal phenotype formation differences between russet and non-russet apples

The apple is an economically important fruit, and fruit russeting is not conducive to its appearance. Although studies have examined fruit russeting, its mechanism remains unclear. Two apple strains of the F1 hybrid population derived from 'Fuji' and 'Golden Delicious' were used in this study. We found that the skin of russet apples was rough and fissured, while that of non-russet apples was smooth and waxy. Chemical staining, LC- and GC-MS showed that both lignin and suberin were increased in russet apple skin. Meanwhile, genes involved in lignin and suberin synthetic pathways were upregulated in russet apple skin. Additionally, we found many differentially expressed genes (DEGs1) involved in hormone biosynthesis and signaling and stress responses in the two apple strains. We found that WRKY13 may influence russeting by regulating lignin synthesis. Our study identified several candidate metabolites and genes, which will provide a good foundation for further research.

Transcriptome and metabolome analyses of lignin biosynthesis mechanism of Platycladus orientalis.

Platycladus orientalis, as an important plant for ecological protection, is a pioneer tree species for afforestation in arid and barren mountainous areas. Lignin has the functions of water and soil conservation, strengthening plant mechanical strength and resisting adverse environmental effects and plays an important role in the ecological protection benefits of P. orientalis. In this study, annual dynamic observations of the lignin content in roots, stems and leaves of one-year-old seedlings of a P. orientalis half-sib family were carried out, and combined transcriptome and metabolome analyses were carried out during three key stages of P. orientalis stem development. The lignin contents in roots, stems and leaves of P. orientalis showed extremely significant spatiotemporal differences. In the stems, lignin was mainly distributed in the cell walls of the pith, xylem, phloem, pericyte, and epidermis, with differences in different periods. A total of 226 metabolites were detected in the stem of P. orientalis, which were divided into seven categories, including 10 synthetic precursor compounds containing lignin. Among them, the content of coniferyl alcohol was the highest, accounting for 12.27% of the total content, and caffeyl alcohol was the lowest, accounting for 7.05% only. By annotating the KEGG functions, a large number of differentially expressed genes and differential metabolites were obtained for the comparison combinations, and seven key enzymes and 24 related genes involved in the process of lignin synthesis in P. orientalis were selected. Based on the results of the metabolic mechanism of lignin in P. orientalis by biochemical, anatomical and molecular biological analyzes, the key regulatory pathways of lignin in P. orientalis were identified, which will be of great significance for regulating the lignin content of P. orientalis and improving the adaptability and resistance of this plant.

Transcriptional and Metabolic Characterization of Feeding Ramie Growth Enhanced by a Combined Application of Gibberellin and Ethrel.

Feeding ramie cultivars (Boehmaria nivea L.) are an important feedstock for livestock. Increasing their biomass and improving their nutritional values are essential for animal feeding. Gibberellin (GA3) and ethylene (ETH) are two plant hormones that regulate the growth, development, and metabolism of plants. Herein, we report effects of the GA3 and ETH application on the growth and plant metabolism of feeding ramie in the field. A combination of GA3 and ETH was designed to spray new plants. The two hormones enhanced the growth of plants to produce more biomass. Meanwhile, the two hormones reduced the contents of lignin in leaves and stems, while increased the content of flavonoids in leaves. To understand the potential mechanisms behind these results, we used RNA-seq-based transcriptomics and UPLC-MS/MS-based metabolomics to characterize gene expression and metabolite profiles associated with the treatment of GA3 and ETH. 1562 and 2364 differentially expressed genes (DEGs) were obtained from leaves and stems (treated versus control), respectively. Meanwhile, 99 and 88 differentially accumulated metabolites (DAMs) were annotated from treated versus control leaves and treated versus control stems, respectively. Data mining revealed that both DEGs and DAMs were associated with multiple plant metabolisms, especially plant secondary metabolism. A specific focus on the plant phenylpropanoid pathway identified candidates of DEGs and DEMs that were associated with lignin and flavonoid biosynthesis. Shikimate hydroxycinnamoyl transferase (HCT) is a key enzyme that is involved in the lignin biosynthesis. The gene encoding B. nivea HCT was downregulated in the treated leaves and stems. In addition, genes encoding 4-coumaryl CoA ligase (4CL) and trans-cinnamate 4-monooxygenase (CYP73A), two lignin pathway enzymes, were downregulated in the treated stems. Meanwhile, the reduction in lignin in the treated leaves led to an increase in cinnamic acid and p-coumaryl CoA, two shared substrates of flavonoids that are enhanced in contents. Taken together, these findings indicated that an appropriate combination of GA3 and ETH is an effective strategy to enhance plant growth via altering gene expression and plant secondary metabolism for biomass-enhanced and value-improved feeding ramie.

High temperature increased lignin contents of poplar (Populus spp) stem via inducing the synthesis caffeate and coniferaldehyde.

Lignin contributes to plant resistance to biotic and abiotic stresses and is dominantly regulated by enzymes which catalyze the generation of metabolites intermediates in lignin synthesis. However, the response of lignin and its key regulatory factors to high temperature stress are poorly understood. Here, this finding revealed that the content of lignin in poplar (Populus spp) stem increased after 3 days of high temperature stress treatment. In fourteen metabolic intermediates of lignin biosynthetic pathway with targeted metabolomics analysis, caffeate and coniferaldehyde increased evidently upon heat stress. C3’H (p-Coumaroylshikimate 3-hydroxylase) and CCR (Cinnamoyl-CoA reductase) are recognized to catalyze the formation of caffeate and coniferaldehyde, respectively. Transcriptome data and RT-qPCR (reverse transcription-quantitative real-time polymerase chain reaction) analysis uncovered the high transcriptional level of PtrMYBs (PtrMYB021, PtrMYB074, PtrMYB85, PtrMYB46), PtrC3’H1 (Potri.006G033300) and PtrCCR2 (Potri.003G181400), suggesting that they played the vital role in the increase of lignin and its metabolic intermediates were induced by high temperature. The discovery of key regulators and metabolic intermediates in lignin pathway that respond to high temperature provides a theoretical basis for quality improvement of lignin and the application of forest resources.

A feast of consequences: Transcriptional and metabolic responses to lignin pathway perturbations.

A feast of consequences: Transcriptional and metabolic responses to lignin pathway perturbations.

Transcriptomic analysis of CO2-treated strawberries (Fragaria vesca) with enhanced resistance to softening and oxidative stress at consumption.

One of the greatest threats to wild strawberries (Fragaria vesca Mara des Bois) after harvest is the highly perishability at ambient temperature. Breeders have successfully met the quality demands of consumers, but the prevention of waste after harvest in fleshy fruits is still pending. Most of the waste is due to the accelerated progress of senescence-like process after harvest linked to a rapid loss of water and firmness at ambient temperature. The storage life of strawberries increases at low temperature, but their quality is limited by the loss of cell structure. The application of high CO2 concentrations increased firmness during cold storage. However, the key genes related to resistance to softening and cell wall disassembly following transference from cold storage at 20°C remain unclear. Therefore, we performed RNA-seq analysis, constructing a weighted gene co-expression network analysis (WGCNA) to identify which molecular determinants play a role in cell wall integrity, using strawberries with contrasting storage conditions, CO2-cold stored (CCS), air-cold stored (ACS), non-cold stored (NCS) kept at ambient temperature, and intact fruit at harvest (AH). The hub genes associated with the cell wall structural architecture of firmer CO2-treated strawberries revealed xyloglucans stabilization attributed mainly to a down-regulation of Csl E1, XTH 15, Exp-like B1 and the maintenance of expression levels of nucleotide sugars transferases such as GMP and FUT as well as improved lamella integrity linked to a down-regulation of RG-lyase, PL-like and PME. The preservation of cell wall elasticity together with the up-regulation of LEA, EXPA4, and MATE, required to maintain cell turgor, is the mechanisms controlled by high CO2. In stressed air-cold stored strawberries, in addition to an acute softening, there is a preferential transcript accumulation of genes involved in lignin and raffinose pathways. Non-cold stored strawberries kept at 20°C after harvest are characterized by an enrichment in genes mainly involved in oxidative stress and up-expression of genes involved in jasmonate biosynthesis. The present results on transcriptomic analysis of CO2-treated strawberries with enhanced resistance to softening and oxidative stress at consumption will help to improve breeding strategies of both wild and cultivated strawberries.

Characteristics and candidate genes associated with excellent stalk strength in maize (Zea mays L.).

Lodging is a major problem in maize production, which seriously affects yield and hinders mechanized harvesting. Improving stalk strength is an effective way to improve lodging. The maize inbred line Jing2416 (J2416) was an elite germplasm in maize breeding which had strong stalk mechanical strength. To explore the characteristics its stalk strength, we conducted physiological, metabolic and transcriptomic analyses of J2416 and its parents Jing24 (J24) and 5237. At the kernel dent stage, the stalk rind penetrometer strength of J2416 was significantly higher than those of its two parents in multiple environments. The rind thickness, sclerenchyma tissue thickness, and cellulose, hemicellulose, and lignin contents of J2416 were significantly higher than those of its parents. Based on the significant differences between J2416 and 5237, we detected metabolites and gene transcripts showing differences in abundance between these two materials. A total of 212 (68.60%) metabolites and 2287 (43.34%) genes were up-regulated in J2416 compared with 5237. The phenylpropanoid and glycan synthesis/metabolism pathways were enriched in metabolites and genes that were up-regulated in J2416. Twenty-eight of the up-regulated genes in J2416 were involved in lignin, cellulose, and hemicellulose synthesis pathways. These analyses have revealed important physiological characteristics and candidate genes that will be useful for research and breeding of inbred lines with excellent stalk strength.

Identification of key enzyme genes involved in biosynthesis pathways of lignan and lignin in Eucommia ulmoides based on transcriptome assembly

Lignan is the main medicinal component of Eucommia ulmoides, and lignin is involved in the defense of plants against diseases and insect pests.They are synthesized from coniferyl alcohol with the help of dirigent(DIR) and peroxidase(POD), respectively.In this study, transcriptome assembly of stems and leaves of E.ulmoides was performed, yielding 112 578 unigenes.Among them, 70 459 were annotated in seven databases.A total of 59 unigenes encodes 11 key enzymes in the biosynthesis pathways of lignin and lignin, of which 11 encode POD and 8 encode DIR.A total of 13 unigenes encoding transcription factors are involved in phenylpropanoid metabolism. Compared with leaves of E.ulmoides, 7 575 unigenes were more highly expressed in stems, of which 462 were involved in phenylpropanoid biosynthesis.Our results extend the public transcriptome dataset of E.ulmoides, which provide valuable information for the analysis of biosynthesis pathways of lignan and lignin in E.ulmoides and lay a foundation for further study on the functions and regulation mechanism of key enzymes in lignan and lignin biosynthesis pathways.