Structural studies of cinnamoyl-CoA reductase and cinnamyl-alcohol dehydrogenase, key enzymes of monolignol biosynthesis

Comprehensive analysis of cinnamoyl-CoA reductase (CCR) gene family in wheat: implications for lignin biosynthesis and stress responses

BACKGROUND

Lignin, the second most abundant terrestrial biopolymer, represents a significant renewable natural biomaterial. Cinnamoyl-CoA reductase (CCR) catalyzes the conversion of various hydroxycinnamoyl-CoA esters into their corresponding aldehydes, utilizing NADPH as a cofactor. CCR functions as a regulatory point that controls the overall carbon flux towards lignin and constitutes the initial committed step in the lignin biosynthesis pathway. Additionally, CCR plays a crucial role in plant development and in resistance to biotic and abiotic stresses. Bread wheat (Triticum aestivum L.), a hexaploid crop, serves as a staple food for much of the global population. However, the copy number variation and expression characteristics of wheat CCR genes remain to be elucidated.

RESULTS

This study identified 115 unique members of the CCR gene family through a comprehensive search of the wheat genome database. Subsequent analyses included the physicochemical properties, chromosomal localizations, gene duplication events, and structures of these genes. Wheat CCRs were categorized into TaCCR and TaCCR-like genes based on phylogenetic comparison, sequence alignment, and protein three-dimensional structure analysis. Twenty TaCCR proteins, characterized by key amino acid residues at the protein catalytic and NADPH-binding sites, were identified as genuine TaCCRs, potentially playing significant roles in lignin biosynthesis. The expression patterns of these 20 TaCCR genes were investigated in various wheat tissues and seedlings subjected to biotic and abiotic stresses. These genes may significantly influence stem development and responses to heat, drought, salt, and pathogen stresses. Additionally, degradome data analysis suggested that the expression of TaCCR6D-1 was regulated by miRNAs. Virus-induced gene silencing experiments demonstrated the involvement of TaCCR5-5 and TaCCR6-1 in wheat lignin synthesis.

CONCLUSIONS

This study presents the first comprehensive identification and analysis of wheat CCR genes. Our findings establish a foundation for further elucidation of TaCCR functions and offer a significant genetic resource for future wheat improvement efforts.

Map-based cloning of Zmccr3 and its network construction and validation for regulating maize seed germination

KEY MESSAGE

Map-based cloning of Zmccr3 for regulate SG and its molecular regulatory pathway was performed and validated. WGCNA, target genes/pathways during the process of seed dormancy formation were obtained. Seed dormancy (SD) and pre-harvest sprouting (PHS) affect the grain yield and quality of grain in cereal and hybrid seed production. Although the benefits of studying SD and seed germination (SG) during seed development are well established, research into the genetic variation and molecular regulation of SD, particularly during the transition from SD to SG, remains very limited. In this study, bulked segregant analysis (BSA) and linkage analysis were used to map the QTL for the maize vp16 mutant of PHS. Using genetic and biological methods, the candidate gene was identified as Zmccr3, encoding cinnamoyl-CoA reductase 3 (ccr3), which is involved in the phenylalanine pathway of lignin metabolism and affects SG. Based on RNA-seq (RNA sequencing) at two stages of grain development with extreme PHS traits, a weighted gene coexpression network analysis (WGCNA) related to SD and SG formation was constructed, and ten target genes and three pathways during the transition from SD to SG were identified. Simultaneously, the Zmccr3 pathway was established and validated, involving upstream lipid metabolism, redox modification and degradation of cell wall oligosaccharides (as electrophilic compounds), regulation of GA signaling and intracellular ROS homeostasis, and downstream oxidation of cell wall lignin units and synthesis of phenolic compounds that affect endosperm weakening and cell wall loosening, ultimately regulating SG or SD. Therefore, we propose the Zmccr3 hypothesis to elucidate its possible functions. These findings have important theoretical and practical implications for understanding the genetic basis of PHS and SD in maize, increasing genetic resources and improving traits.

Genome-wide identification and expression pattern analysis of the cinnamoyl-CoA reductase gene family in flax (Linum usitatissimum L.)

BACKGROUND

Cinnamoyl-CoA reductase (CCR) is the first important and committed enzyme in the monolignol synthesis branch of the lignin biosynthesis (LB) pathway, catalyzing the conversion of cinnamoyl-CoAs to cinnamaldehydes and is crucial for the growth of Linum usitatissimum (flax), an important fiber crop. However, little information is available about CCR in flax (Linum usitatissimum L.).

RESULTS

In this study, we conducted a genome-wide analysis of the CCR gene family and identified a total of 22 CCR genes. The 22 CCR genes were distributed across 9 chromosomes, designated LuCCR1-LuCCR22. Multiple sequence alignment and conserved motif analyses revealed that LuCCR7/13/15/20 harbor completely conserved NADP-specific, NAD(P)-binding, and CCR signature motifs. Furthermore, each of these LuCCRs is encoded by 5 exons separated by 4 introns, a characteristic feature of functional CCRs. Phylogenetic analysis grouped LuCCRs into two clades, with LuCCR7/13/15/20 clustering with functional CCRs involved in LB in dicotyledonous plants. RNA-seq analysis indicated that LuCCR13/20 genes are highly expressed throughout all flax developmental stages, particularly in lignified tissues such as roots and stems, with increased expression during stem maturation. These findings suggest that LuCCR13/20 play crucial roles in the biosynthesis process of flax lignin. Additionally, LuCCR2/5/10/18 were upregulated under various types of abiotic stress, highlighting their potential roles in flax defense-related processes.

CONCLUSIONS

This study systematically analyzes the CCR gene family (CCRGF) of flax (Linum usitatissimum L.) at the genomic level for the first time, so as to select the whole members of the CCRGF of flax and to ascertain their potential roles in lignin synthesis. Therefore, in future work, we can target genetic modification of LuCCR13/20 to optimize the content of flax lignin. As such, this research establishes a theoretical foundation for studying LuCCR gene functions and offers a new perspective for cultivating low-lignin flax varieties.

Systematic characterization of cinnamyl alcohol dehydrogenase members revealed classification and function divergence in Haplomitrium mnioides

Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) is considered to be a key enzyme in lignin biosynthesis, which can catalyze cinnamyl aldehyde to produce cinnamyl alcohol. In this study, three putative CADs were characterized from the liverwort Haplomitrium mnioides. The sequence alignment and phylogenetic analysis revealed that HmCADs belonged to a multigene family, with three HmCADs belonging to class II, class III, and class IV, respectively. In vitro enzymatic studies demonstrated that HmCAD2 exhibited high affinity and catalytic activity towards five cinnamyl aldehydes, followed by HmCAD3 with poor catalytic activity, and HmCAD1 catalyzed only the reaction of p-coumaryl aldehyde and coniferyl aldehyde with extremely low catalytic capacity. Protein-substrate binding simulations were performed to investigate the differences in catalytic activity exhibited when proteins catalyzed different substrates. Furthermore, distinct expression patterns of three HmCADs were identified in different plant tissues. Subcellular localization tests confirmed that HmCAD1/2/3 was located in the cytoplasm. The simulated responses of HmCADs to different stresses showed that HmCAD1 played a positive role in coping with each stress, while HmCAD2/3 was weak. These findings demonstrate the diversity of CADs in liverwort, highlight the divergent role of HmCAD1/2/3 in substrate catalysis, and also suggest their possible involvement in stress response, thereby providing new insights into CAD evolution while emphasizing their potential distinctive and collaborative contributions to the normal growth of primitive liverworts.

Floral volatile benzenoids/phenylpropanoids: biosynthetic pathway, regulation and ecological value

Benzenoids/phenylpropanoids, the second most diverse group of plant volatiles, exhibit significant structural diversity and play crucial roles in attracting pollinators and protecting against pathogens, insects, and herbivores. This review summarizes their complex biosynthetic pathways and regulatory mechanisms, highlighting their links to plant growth, development, hormone levels, circadian rhythms, and flower coloration. External factors like light, humidity, and temperature also influence their biosynthesis. Their ecological value is discussed, offering insights for enhancing floral scent, pollinator attraction, pest resistance, and metabolic engineering through genetic modification.

How lignin biosynthesis responds to nitrogen in plants: a scoping review

Nitrogen (N) plays a critical role in the functioning of key amino acids and synthetic enzymes responsible for the various stages of lignin biosynthesis. However, the precise mechanisms through which N influences lignin biosynthesis have not been fully elucidated. This scoping review explores how lignin biosynthesis responds to N in plants. A systematic search of the literature in several databases was conducted using relevant keywords. Only 44 of the 1842 selected studies contained a range of plant species, experimental conditions, and research approaches. Lignin content, structure, and biosynthetic pathways in response to N are discussed, and possible response mechanisms of lignin under low N are proposed. Among the selected studies, 64.52% of the studies reter to lignin content found a negative correlation between N availability and lignin content. Usually, high N decreases the lignin content, delays cell lignification, increases p-hydroxyphenyl propane (H) monomer content, and regulates lignin synthesis through the expression of key genes (PAL, 4CL, CCR, CAD, COMT, LAC, and POD) encoding miRNAs and transcription factors (e.g., MYB, bHLH). N deficiency enhances lignin synthesis through the accumulation of phenylpropanoids, phenolics, and soluble carbohydrates, and indirect changes in phytohormones, secondary metabolites, etc. This review provides new insights and important references for future studies on the regulation of lignin biosynthesis.

In vivo assembly in tobacco cells to elucidate and engineer the biosynthesis of 4-hydroxydihydrocinnamaldehyde from Gloriosa superba

KEY MESSAGE

This study described the biosynthesis of 4-hydroxydihydrocinnamaldehyde sharing with monolignol pathway and supplemented the biosynthesis of colchicine in G. superba, 4-hydroxydihydrocinnamaldehyde produced in tobacco BY2 cells provided an important stepstone. The precursor, 4-hydroxydihydrocinnamaldehyde (4-HDCA), participates in the biosynthesis of the carbon skeleton of colchicine, which is derived from L-phenylalanine. However, one hypothesis proposed that 4-HDCA is synthesized by sharing the early part of the monolignol pathway in G. superba. In this study, we validated this prediction and identified the enzymatic functions involved in this pathway. GsDBR1 is a crucial enzyme to illustrate 4-HDCA diverging from monolignol pathway, we first confirmed its reductase activity on 4-coumaraldehyde, an important intermediate compound in monolignol biosynthesis. Then, the biochemical function of recombinant enzymes belonging to the other four families were verified to elucidate the entire process of 4-HDCA biosynthesis from L-phenylalanine. After reconstruction, the 4-HDCA was 78.4 ng/g with fresh weight (FW) of transgenic tobacco cells, and the yield increased to 168.22 ng/g·FW after improved treatment with methyl jasmonate (MeJA). The elucidation of 4-HDCA biosynthesis sharing the monolignol pathway supplemented the biosynthesis of colchicine in G. superba, and the production of 4-HDCA in tobacco cells provides an important step in the development of plant cell cultures as heterologous bio-factories for secondary metabolite production.

Identification of a cinnamoyl-CoA reductase from Cinnamomum cassia involved in trans-cinnamaldehyde biosynthesis

MAIN CONCLUSION

The identification of a functional cinnamoyl-CoA reductase enzyme from Cinnamomum cassia involved in trans-cinnamaldehyde biosynthesis offers the potential for enhancing trans-cinnamaldehyde production through genetic engineering. A significant accumulation of trans-cinnamaldehyde has been found in the bark tissues of C. cassia, used in traditional Chinese medicine. trans-Cinnamaldehyde exhibits various pharmacological properties such as anti-inflammatory, analgesic, and protection of the stomach and the digestive tract. However, further elucidation and characterization of the biosynthetic pathway for trans-cinnamaldehyde is required. In this study, we conducted an integrated analysis of trans-cinnamaldehyde accumulation profiles and transcriptomic data from five different C. cassia tissues to identify the genes involved in its biosynthesis. The transcriptome data we obtained included nearly all genes associated with the trans-cinnamaldehyde pathway, with the majority demonstrating high abundance in branch barks and trunk barks. We successfully cloned four C. cassia cinnamoyl-CoA reductases (CcCCRs), a key gene in trans-cinnamaldehyde biosynthesis. We found that the recombinant CcCCR1 protein was the only one that more efficiently converted cinnamoyl-CoA into trans-cinnamaldehyde. CcCCR1 exhibited approximately 14.7-fold higher catalytic efficiency (kcat/Km) compared to the Arabidopsis thaliana cinnamoyl-CoA reductase 1 (AtCCR1); therefore, it can be utilized for engineering higher trans-cinnamaldehyde production as previously reported. Molecular docking studies and mutagenesis experiments also validated the superior catalytic activity of CcCCR1 compared to AtCCR1. These findings provide valuable insights for the functional characterization of enzyme-coding genes and hold potential for future engineering of trans-cinnamaldehyde biosynthetic pathways.

Artificial Biosynthetic Pathway for Efficient Synthesis of Vanillin, a Feruloyl-CoA-Derived Natural Product from Eugenol

Eugenol, the main component of essential oil from the Syzygium aromaticum clove tree, has great potential as an alternative bioresource feedstock for biosynthesis purposes. Although eugenol degradation to ferulic acid was investigated, an efficient method for directly converting eugenol to targeted natural products has not been established. Herein we identified the inherent inhibitions by simply combining the previously reported ferulic acid biosynthetic pathway and vanillin biosynthetic pathway. To overcome this, we developed a novel biosynthetic pathway for converting eugenol into vanillin, by introducing cinnamoyl-CoA reductase (CCR), which catalyzes conversion of coniferyl aldehyde to feruloyl-CoA. This approach bypasses the need for two catalysts, namely coniferyl aldehyde dehydrogenase and feruloyl-CoA synthetase, thereby eliminating inhibition while simplifying the pathway. To further improve efficiency, we enhanced CCR catalytic efficiency via directed evolution and leveraged an artificialvanillin biosensor for high-throughput screening. Switching the cofactor preference of CCR from NADP+ to NAD+ significantly improved pathway efficiency. This newly designed pathway provides an alternative strategy for efficiently biosynthesizing feruloyl-CoA-derived natural products using eugenol.

Integrated Metabolome and Transcriptome Analysis of Gibberellins Mediated the Circadian Rhythm of Leaf Elongation by Regulating Lignin Synthesis in Maize

Plant growth exhibits rhythmic characteristics, and gibberellins (GAs) are involved in regulating cell growth, but it is still unclear how GAs crosstalk with circadian rhythm to regulate cell elongation. The study analyzed growth characteristics of wild-type (WT), zmga3ox and zmga3ox with GA3 seedlings. We integrated metabolomes and transcriptomes to study the interaction between GAs and circadian rhythm in mediating leaf elongation. The rates of leaf growth were higher in WT than zmga3ox, and zmga3ox cell length was shorter when proliferated in darkness than light, and GA3 restored zmga3ox leaf growth. The differentially expressed genes (DEGs) between WT and zmga3ox were mainly enriched in hormone signaling and cell wall synthesis, while DEGs in zmga3ox were restored to WT by GA3. Moreover, the number of circadian DEGs that reached the peak expression in darkness was more than light, and the upregulated circadian DEGs were mainly enriched in cell wall synthesis. The differentially accumulated metabolites (DAMs) were mainly attributed to flavonoids and phenolic acid. Twenty-two DAMs showed rhythmic accumulation, especially enriched in lignin synthesis. The circadian DEGs ZmMYBr41/87 and ZmHB34/70 were identified as regulators of ZmHCT8 and ZmBM1, which were enzymes in lignin synthesis. Furthermore, GAs regulated ZmMYBr41/87 and ZmHB34/70 to modulate lignin biosynthesis for mediating leaf rhythmic growth.

Effects of exogenous GA3 on stem secondary growth of Pinus massoniana seedlings

Gibberellins (GAs) play a crucial role in regulating secondary growth in angiosperms, but their effects on the secondary growth of gymnosperms are rarely reported. In this study, we administered exogenous GA3 to two-year-old P. massoniana seedlings, and examined its effects on anatomical structure, physiological and biochemical changes, and gene expression in stems. The results showed that exogenous GA3 could enhance xylem development in P. massoniana by promoting cell division. The content of endogenous hormone (including auxins, brassinosteroids, and gibberellins) were changed and the genes related to phytohormone biosynthesis and signaling pathway, such as GID1, DELLA, TIR1, ARF, SAUR, CPD, BR6ox1, and CYCD3, were differentially expressed under GA3 treatment. Furthermore, GA3 and BR (brassinosteroid) might act synergistically in promoting secondary growth in P. massoniana. Additionally, lignin content was significantly increased after GA3 treatment accompanied by the express of lignin biosynthesis related genes. PmCAD (TRINITY_DN142116_c0_g1), a crucial gene involved in the lignin biosynthesis, was cloned and overexpressed in Nicotiana benthamiana, significantly promoting the xylem development and enhancing stem lignification. It was regarded as a key candidate gene for improving stem growth of P. massoniana. The findings of this study have demonstrated the impact of GA3 treatment on secondary growth of stems in P. massoniana, providing a foundation for understanding the molecular regulatory mechanism of stem secondary growth in Pinaceae seedlings and offering theoretical guidance for cultivating new germplasm with enhanced growth and yield.

Microparticle-mediated CRISPR DNA delivery for genome editing in poplar

The use of CRISPR/Cas9 is currently the method of choice for precise genome engineering in plants, including in the biomass crop poplar. The most commonly used method for delivering CRISPR/Cas9 and its components in poplar is via Agrobacterium-mediated transformation, that besides the desired gene-editing event also results in stable T-DNA integration. Here we explore the delivery of the gene-editing reagents via DNA-coated microparticle bombardment into the model tree Populus tremula x P. alba to evaluate its potential for developing transgene-free, gene-edited trees, as well as its potential for integrating donor DNA at specific target sites. Using an optimized transformation method, which favors the regeneration of plants that transiently express the genes on the delivered donor DNA, we regenerated gene-edited plants that are free of the Cas9 and the antibiotic resistance-encoding transgenes. In addition, we report the frequent integration of donor DNA fragments at the Cas9-induced double-strand break, opening opportunities toward targeted gene insertions.

Structural Similarities and Overlapping Activities among Dihydroflavonol 4-Reductase, Flavanone 4-Reductase, and Anthocyanidin Reductase Offer Metabolic Flexibility in the Flavonoid Pathway

Flavonoids are potent antioxidants that play a role in defense against pathogens, UV-radiation, and the detoxification of reactive oxygen species. Dihydroflavonol 4-reductase (DFR) and flavanone 4-reductase (FNR) reduce dihydroflavonols and flavanones, respectively, using NAD(P)H to produce flavan-(3)-4-(di)ols in flavonoid biosynthesis. Anthocyanidin reductase (ANR) reduces anthocyanidins to flavan-3-ols. In addition to their sequences, the 3D structures of recombinant DFR, FNR and ANR from sorghum and switchgrass showed a high level of similarity. The catalytic mechanism, substrate-specificity and key residues of three reductases were deduced from crystal structures, site-directed mutagenesis, molecular docking, kinetics, and thermodynamic ana-lyses. Although DFR displayed its highest activity against dihydroflavonols, it also showed activity against flavanones and anthocyanidins. It was inhibited by the flavonol quercetin and high concentrations of dihydroflavonols/flavonones. SbFNR1 and SbFNR2 did not show any activity against dihydroflavonols. However, SbFNR1 displayed activity against flavanones and ANR activity against two anthocyanidins, cyanidin and pelargonidin. Therefore, SbFNR1 and SbFNR2 could be specific ANR isozymes without delphinidin activity. Sorghum has high concentrations of 3-deoxyanthocyanidins in vivo, supporting the observed high activity of SbDFR against flavonols. Mining of expression data indicated substantial induction of these three reductase genes in both switchgrass and sorghum in response to biotic stress. Key signature sequences for proper DFR/ANR classification are proposed and could form the basis for future metabolic engineering of flavonoid metabolism.

Bioinformatic analysis of short-chain dehydrogenase/reductase proteins in plant peroxisomes

Peroxisomes are ubiquitous eukaryotic organelles housing not only many important oxidative metabolic reactions, but also some reductive reactions that are less known. Members of the short-chain dehydrogenase/reductase (SDR) superfamily, which are NAD(P)(H)-dependent oxidoreductases, play important roles in plant peroxisomes, including the conversion of indole-3-butyric acid (IBA) to indole-3-acetic acid (IAA), auxiliary β-oxidation of fatty acids, and benzaldehyde production. To further explore the function of this family of proteins in the plant peroxisome, we performed an in silico search for peroxisomal SDR proteins from Arabidopsis based on the presence of peroxisome targeting signal peptides. A total of 11 proteins were discovered, among which four were experimentally confirmed to be peroxisomal in this study. Phylogenetic analyses showed the presence of peroxisomal SDR proteins in diverse plant species, indicating the functional conservation of this protein family in peroxisomal metabolism. Knowledge about the known peroxisomal SDRs from other species also allowed us to predict the function of plant SDR proteins within the same subgroup. Furthermore, in silico gene expression profiling revealed strong expression of most SDR genes in floral tissues and during seed germination, suggesting their involvement in reproduction and seed development. Finally, we explored the function of SDRj, a member of a novel subgroup of peroxisomal SDR proteins, by generating and analyzing CRISPR/Cas mutant lines. This work provides a foundation for future research on the biological activities of peroxisomal SDRs to fully understand the redox control of peroxisome functions.

A novel 7-base pair deletion at a splice site in MS-2 impairs male fertility via premature tapetum degradation in common bean (Phaseolis vulgaris L.)

A novel splice-site mutation in the P. vulgarisgene for TETRAKETIDE α-PYRONE REDUCTASE 2 impairs male fertility, and parthenocarpic pod development can be improved by external application of IAA. Snap bean (Phaseolus vulgaris L.) is an important vegetable crop in many parts of the world, and the main edible part is the fresh pod. Here, we report the characterization of the genic male sterility (ms-2) mutant in common bean. Loss of function of MS-2 accelerates degradation of the tapetum, resulting in a complete male sterility. Through fine-mapping, co-segregation, and re-sequencing analysis, we identified Phvul.003G032100, which encodes the TETRAKETIDE α-PYRONE REDUCTASE 2 (PvTKPR2) protein in common bean, as the causal gene for MS-2. PvTKPR2 is predominantly expressed at the early stages of flower development. A novel 7-bp (+ 6028 bp to + 6034 bp) deletion mutation spans the splice site between the fourth intron and fifth exon, leading to a 9-bp deletion in transcribed mRNA and a 3-amino acid (G210M211V212) deletion in the protein coding sequence of the PvTKPR2^ms-2 gene. The 3-D structural changes in the protein due to the mutation may impair the activities of NAD-dependent epimerase/dehydratase and the NAD(P)-binding domains of PvTKPR2^ms-2 protein. The ms-2 mutant plants produce many small parthenocarpic pods, and the size of the pods can be doubled by external application of 2 mM indole-3-acetic acid (IAA). Our results demonstrate that a novel mutation in PvTKPR2 impairs male fertility through premature degradation of the tapetum.

OsCCRL1 is Essential for Phenylpropanoid Metabolism in Rice Anthers

Phenylpropanoid metabolism and timely tapetal degradation are essential for anther and pollen development, but the underlying mechanisms are unclear. In the current study, to investigate this, we identified and analyzed the male-sterile mutant, osccrl1 (cinnamoyl coA reductase-like 1), which exhibited delayed tapetal programmed cell death (PCD) and defective mature pollen. Map-based cloning, genetic complementation, and gene knockout revealed that OsCCRL1 corresponds to the gene LOC_Os09g32020.2, a member of SDR (short-chain dehydrogenase/reductase) family enzyme. OsCCRL1 was preferentially expressed in the tapetal cells and microspores, and localized to the nucleus and cytoplasm in both rice protoplasts and Nicotiana benthamiana leaves. The osccrl1 mutant exhibited reduced CCRs enzyme activity, less lignin accumulation, delayed tapetum degradation, and disrupted phenylpropanoid metabolism. Furthermore, an R2R3 MYB transcription factor OsMYB103/OsMYB80/OsMS188/BM1, involved in tapetum and pollen development, regulates the expression of OsCCRL1. Finally, the osmyb103 osccrl1 double mutants, exhibited the same phenotype as the osmyb103 single mutant, further indicating that OsMYB103/OsMYB80/OsMS188/BM1 functions upstream of OsCCRL1. These findings help to clarify the role of phenylpropanoid metabolism in male sterility and the regulatory network underlying the tapetum degradation.

Molecular cloning and characterization of Cinnamoyl-CoA reductase promoter gene from Asarum sieboldii Miq

Asarum sieboldii Miq., a perennial herb of the family Aristolochiaceae, is widely used in China to treat cold, fever, aphthous stomatitis, toothache, gingivitis, and rheumatoid arthritis. Methyleugenol is the most representative pharmacological constituent of this medicinal herb. Cinnamoyl-CoA reductase (CCR), which has been well known for occupying a critical position in the lignin biosynthesis pathway, is also shared with the biosynthesis of methyleugenol. To better understand the regulatory mechanisms of methyleugenol biosynthesis, a 1530-bp long promoter region of the AsCCR1 gene was isolated. PLACE and PlantCARE analysis affirmed the existence of the core promoter elements such as TATA and CAAT boxes, abiotic stress-responsive cis-regulation elements like abscisic acid-responsive element, G-box, and MBS in the isolated sequence. The histochemical assay suggested that it was a constitutive promoter, highly expressed in the root tissue. Moreover, the region of -200 bp to ATG (start codon) was enough to drive the expression of It GUS gene. Treatments with low temperature and high concentration of gibberellin or abscisic acid demonstrated the abiotic stress-induced expression of the AsCCR1 promoter. Overall, this study revealed the isolation and characterization of the AsCCR1 promoter. Moreover, it also provided a candidate gene for molecular breeding in A. sieboldii to enhance its pharmacological potential.

Genome-wide identification, characterization, and genetic diversity of CCR gene family in Dalbergia odorifera

INTRODUCTION

Lignin is a complex aromatic polymer plays major biological roles in maintaining the structure of plants and in defending them against biotic and abiotic stresses. Cinnamoyl-CoA reductase (CCR) is the first enzyme in the lignin-specific biosynthetic pathway, catalyzing the conversion of hydroxycinnamoyl-CoA into hydroxy cinnamaldehyde. Dalbergia odorifera T. Chen is a rare rosewood species for furniture, crafts and medicine. However, the CCR family genes in D. odorifera have not been identified, and their function in lignin biosynthesis remain uncertain.

METHODS AND RESULTS

Here, a total of 24 genes, with their complete domains were identified. Detailed sequence characterization and multiple sequence alignment revealed that the DoCCR protein sequences were relatively conserved. They were divided into three subfamilies and were unevenly distributed on 10 chromosomes. Phylogenetic analysis showed that seven DoCCRs were grouped together with functionally characterized CCRs of dicotyledons involved in developmental lignification. Synteny analysis showed that segmental and tandem duplications were crucial in the expansion of CCR family in D. odorifera, and purifying selection emerged as the main force driving these genes evolution. Cis-acting elements in the putative promoter regions of DoCCRs were mainly associated with stress, light, hormones, and growth/development. Further, analysis of expression profiles from the RNA-seq data showed distinct expression patterns of DoCCRs among different tissues and organs, as well as in response to stem wounding. Additionally, 74 simple sequence repeats (SSRs) were identified within 19 DoCCRs, located in the intron or untranslated regions (UTRs), and mononucleotide predominated. A pair of primers with high polymorphism and good interspecific generality was successfully developed from these SSRs, and 7 alleles were amplified in 105 wild D. odorifera trees from 17 areas covering its whole native distribution.

DISCUSSION

Overall, this study provides a basis for further functional dissection of CCR gene families, as well as breeding improvement for wood properties and stress resistance in D. odorifera.

Characterization, Expression Profiling, and Biochemical Analyses of the Cinnamoyl-CoA Reductase Gene Family for Lignin Synthesis in Alfalfa Plants

Cinnamoyl-CoA reductase (CCR) is a pivotal enzyme in plant lignin synthesis, which has a role in plant secondary cell wall development and environmental stress defense. Alfalfa is a predominant legume forage with excellent quality, but the lignin content negatively affects fodder digestibility. Currently, there is limited information on CCR characteristics, gene expression, and its role in lignin metabolism in alfalfa. In this study, we identified 30 members in the CCR gene family of Medicago sativa. In addition, gene structure, conserved motif, and evolution analysis suggested MsCCR1–7 presumably functioned as CCR, while the 23 MsCCR-likes fell into three categories. The expression patterns of MsCCRs/MsCCR-likes suggested their role in plant development, response to environmental stresses, and phytohormone treatment. These results were consistent with the cis-elements in their promoters. Histochemical staining showed that lignin accumulation gradually deepened with the development, which was consistent with gene expression results. Furthermore, recombinant MsCCR1 and MsCCR-like1 were purified and the kinetic parameters were tested under four substrates. In addition, three-dimensional structure models of MsCCR1 and MsCCR-like1 proteins showed the difference in the substrate-binding motif H212(X)2K215R263. These results will be useful for further application for legume forage quality modification and biofuels industry engineering in the future.

Phylogeny and functional characterization of the cinnamyl alcohol dehydrogenase gene family in Phryma leptostachya

Phryma leptostachya has attracted increasing attention because it is rich in furofuran lignans with a wide range of biological activities. Biosynthesis of furofuran lignans begins with the dimerization of coniferyl alcohol, one of the monolignol. Cinnamyl alcohol dehydrogenase (CAD) catalyzes the final step of monolignol biosynthesis, reducing cinnamyl aldehydes to cinnamyl alcohol. As it is in the terminal position of monolignol biosynthesis, its type and activity can cause significant changes in the total amount and composition of lignans. Herein, combined with bioinformatics analysis and in vitro enzyme assays, we clarified that CAD in P. leptostachya belonged to a multigene family, and identified nearly the entire CAD gene family. Our in-depth characterization about the functions and structures of two major CAD isoforms, PlCAD2 and PlCAD3, showed that PlCAD2 exhibited the highest catalytic activity, and coniferyl aldehyde was its preferred substrate, followed by PlCAD3, and sinapyl aldehyde was its preferred substrate. Considering the accumulation patterns of furofuran lignans and expression patterns of PlCADs, we speculated that PlCAD2 was the predominant CAD isoform responsible for furofuran lignans biosynthesis in P. leptostachya. Moreover, these CADs found here can also provide effective biological parts for lignans and lignins biosynthesis.

Molecular Mechanisms of Phenylpropane-Synthesis-Related Genes Regulating the Shoot Blight Resistance of Bambusa pervariabilis × Dendrocalamopsis grandis

Bambusa pervariabilis × Dendrocalamopsis grandis shoot blight caused by Arthrinium phaeospermum is a fungal disease that has affected a large area in China in recent years. However, it is not clear which genes are responsible for the disease resistance of B. pervariabilis × D. grandis. Based on the analysis of transcriptome and proteome data, two genes, CCoAOMT2 and CAD5, which may be involved in disease resistance, were screened. Two gene expression-interfering varieties, COF RNAi and CAD RNAi were successfully obtained using RNAi technology. Quantitative real-time fluorescence (qRT-PCR) results showed that CCoAOMT2 gene, CAD5 gene and seven related genes expression was down-regulated in the transformed varieties. After inoculating pathogen spore suspension, the incidence and disease index of cof-RNAi and cad-RNAi transformed plants increased significantly. At the same time, it was found that the content of total lignin and flavonoids in the two transformed varieties were significantly lower than that of the wild-type. The subcellular localization results showed that both CCoAOMT2 and CAD5 were localized in the nucleus and cytoplasm. The above results confirm that the CCoAOMT2 and CAD5 genes are involved in the resistance of B. pervariabilis × D.grandis to shoot blight through regulating the synthesis of lignin and flavonoids.

A peroxisomal heterodimeric enzyme is involved in benzaldehyde synthesis in plants

Benzaldehyde, the simplest aromatic aldehyde, is one of the most wide-spread volatiles that serves as a pollinator attractant, flavor, and antifungal compound. However, the enzyme responsible for its formation in plants remains unknown. Using a combination of in vivo stable isotope labeling, classical biochemical, proteomics and genetic approaches, we show that in petunia benzaldehyde is synthesized via the β-oxidative pathway in peroxisomes by a heterodimeric enzyme consisting of α and β subunits, which belong to the NAD(P)-binding Rossmann-fold superfamily. Both subunits are alone catalytically inactive but, when mixed in equal amounts, form an active enzyme, which exhibits strict substrate specificity towards benzoyl-CoA and uses NADPH as a cofactor. Alpha subunits can form functional heterodimers with phylogenetically distant β subunits, but not all β subunits partner with α subunits, at least in Arabidopsis. Analysis of spatial, developmental and rhythmic expression of genes encoding α and β subunits revealed that expression of the gene for the α subunit likely plays a key role in regulating benzaldehyde biosynthesis.

Benzaldehyde is a simple aromatic aldehyde that attracts pollinators, has antifungal properties and contributes to flavor in many plants. Here the authors show that benzaldehyde is synthesized in petunia via the benzoic acid β-oxidative pathway by a peroxisomal heterodimeric enzyme consisting of α and β subunits.

Identification and Characterization of Cinnamyl Alcohol Dehydrogenase Encoding Genes Involved in Lignin Biosynthesis and Resistance to Verticillium dahliae in Upland Cotton (Gossypium hirsutum L.)

Verticillium wilt, caused by the soil-borne fungus Verticillium dahliae, is one of the most devastating diseases in cotton (Gossypium spp.). Lignin in the cell wall forms a physical barrier to inhibit pathogen invasion, and defense-induced lignification reinforces secondary cell wall to prevent pathogens from further spreading. Cinnamyl alcohol dehydrogenases (CADs) catalyze the production of three main monolignols, p-coumaryl- (H), coniferyl- (G), and sinapyl-alcohols (S), which are the fundamental blocks of lignin. Here, we identified CAD genes in G. hirsutum, analyzed their expression profiles in cotton leaf, stem, and root from different developmental stages, and selected GhCAD35, GhCAD45, and GhCAD43, which were consistently induced by V. dahliae inoculation in G. hirsutum cultivars resistant or susceptible to V. dahliae. On the basis of confirmation of the in vitro enzymatic activity of the three proteins in generation of the three monolignols, we used virus-induced gene silencing (VIGS) to investigate the effects of silencing of GhCAD35, GhCAD45, or GhCAD43 on resistance to V. dahliae as well as on deposition and the composition of lignin. Silencing each of the three CADs impaired the defense-induced lignification and salicylic acid biosynthesis in stem, and compromised resistance to V. dahliae. Moreover, our study showed that silencing the three GhCADs severely affected the biosynthesis of S-lignin, leading to a decrease of the syringyl/guaiacyl (S/G) ratio. Heterogeneous overexpression of GhCAD35, GhCAD45, or GhCAD43 in Arabidopsis enhanced disease resistance. Taken together, our study demonstrates a role of the three GhCADs in defense-induced lignin biosynthesis and resistance to V. dahliae in G. hirsutum.

Integrated de novo Analysis of Transcriptional and Metabolic Variations in Salt-Treated Solenostemma argel Desert Plants

Solenostemma argel (Delile) Hayne is a desert plant that survives harsh environmental conditions with several vital medicinal properties. Salt stress is a major constraint limiting agricultural production around the globe. However, response mechanisms behind the adaptation of S. argel plants to salt stress are still poorly understood. In the current study, we applied an omics approach to explore how this plant adapts to salt stress by integrating transcriptomic and metabolomic changes in the roots and leaves of S. argel plants under salt stress. De novo assembly of transcriptome produced 57,796 unigenes represented by 165,147 transcripts/isoforms. A total of 730 differentially expressed genes (DEGs) were identified in the roots (396 and 334 were up- and down-regulated, respectively). In the leaves, 927 DEGs were identified (601 and 326 were up- and down-regulated, respectively). Gene ontology and Kyoto Encyclopedia of Genes And Genomes pathway enrichment analyses revealed that several defense-related biological processes, such as response to osmotic and oxidative stress, hormonal signal transduction, mitogen-activated protein kinase signaling, and phenylpropanoid biosynthesis pathways are the potential mechanisms involved in the tolerance of S. argel plants to salt stress. Furthermore, liquid chromatography-tandem mass spectrometry was used to detect the metabolic variations of the leaves and roots of S. argel under control and salt stress. 45 and 56 critical metabolites showed changes in their levels in the stressed roots and leaves, respectively; there were 20 metabolites in common between the roots and leaves. Differentially accumulated metabolites included amino acids, polyamines, hydroxycinnamic acids, monolignols, flavonoids, and saccharides that improve antioxidant ability and osmotic adjustment of S. argel plants under salt stress. The results present insights into potential salt response mechanisms in S. argel desert plants and increase the knowledge in order to generate more tolerant crops to salt stress.

Underwater CAM photosynthesis elucidated by Isoetes genome

To conserve water in arid environments, numerous plant lineages have independently evolved Crassulacean Acid Metabolism (CAM). Interestingly, Isoetes, an aquatic lycophyte, can also perform CAM as an adaptation to low CO2 availability underwater. However, little is known about the evolution of CAM in aquatic plants and the lack of genomic data has hindered comparison between aquatic and terrestrial CAM. Here, we investigate underwater CAM in Isoetes taiwanensis by generating a high-quality genome assembly and RNA-seq time course. Despite broad similarities between CAM in Isoetes and terrestrial angiosperms, we identify several key differences. Notably, Isoetes may have recruited the lesser-known 'bacterial-type' PEPC, along with the 'plant-type' exclusively used in other CAM and C4 plants for carboxylation of PEP. Furthermore, we find that circadian control of key CAM pathway genes has diverged considerably in Isoetes relative to flowering plants. This suggests the existence of more evolutionary paths to CAM than previously recognized.

The evolution of the phenylpropanoid pathway entailed pronounced radiations and divergences of enzyme families

Land plants constantly respond to fluctuations in their environment. Part of their response is the production of a diverse repertoire of specialized metabolites. One of the foremost sources for metabolites relevant to environmental responses is the phenylpropanoid pathway, which was long thought to be a land-plant-specific adaptation shaped by selective forces in the terrestrial habitat. Recent data have, however, revealed that streptophyte algae, the algal relatives of land plants, have candidates for the genetic toolkit for phenylpropanoid biosynthesis and produce phenylpropanoid-derived metabolites. Using phylogenetic and sequence analyses, we here show that the enzyme families that orchestrate pivotal steps in phenylpropanoid biosynthesis have independently undergone pronounced radiations and divergence in multiple lineages of major groups of land plants; sister to many of these radiated gene families are streptophyte algal candidates for these enzymes. These radiations suggest a high evolutionary versatility in the enzyme families involved in the phenylpropanoid-derived metabolism across embryophytes. We suggest that this versatility likely translates into functional divergence, and may explain the key to one of the defining traits of embryophytes: a rich specialized metabolism.

Prototyping of microbial chassis for the biomanufacturing of high-value chemical targets

Metabolic engineering technologies have been employed with increasing success over the last three decades for the engineering and optimization of industrial host strains to competitively produce high-value chemical targets. To this end, continued reductions in the time taken from concept, to development, to scale-up are essential. Design-Build-Test-Learn pipelines that are able to rapidly deliver diverse chemical targets through iterative optimization of microbial production strains have been established. Biofoundries are employing in silico tools for the design of genetic parts, alongside combinatorial design of experiments approaches to optimize selection from within the potential design space of biological circuits based on multi-criteria objectives. These genetic constructs can then be built and tested through automated laboratory workflows, with performance data analysed in the learn phase to inform further design. Successful examples of rapid prototyping processes for microbially produced compounds reveal the potential role of biofoundries in leading the sustainable production of next-generation bio-based chemicals.

Purification, biochemical characterisation and bioinformatic analysis of recombinant farnesol dehydrogenase from Theobroma cacao

The juvenile hormones (JH) in plants are suggested to act as a form of plant defensive strategy especially against insect herbivory. The oxidation of farnesol to farnesoic acid is a key step in the juvenile hormone biosynthesis pathway. We herein present the purification and characterisation of the recombinant Theobroma cacao farnesol dehydrogenase enzyme that catalyses oxidation of farnesol to farnesal. The recombinant enzyme was purified to apparent homogeneity by affinity chromatography. The purified enzyme was characterised in terms of its deduced amino acid sequences, phylogeny, substrate specificity, kinetic parameters, structural modeling, and docking simulation. The phylogenetic analysis indicated that the T. cacao farnesol dehydrogenase (TcFolDH) showed a close relationship with A. thaliana farnesol dehydrogenase gene. The TcFolDH monomer had a large N-terminal domain which adopted a typical Rossmann-fold, harboring the GxxGxG motif (NADP(H)-binding domain) and a small C-terminal domain. The enzyme was a homotrimer comprised of subunits with molecular masses of 36 kDa. The TcFolDH was highly specific to NADP⁺ as coenzyme. The substrate specificity studies showed trans, trans-farnesol was the most preferred substrate for the TcFolDH, suggesting that the purified enzyme was a NADP⁺-dependent farnesol dehydrogenase. The docking of trans, trans-farnesol and NADP⁺ into the active site of the enzyme showed the important residues, and their interactions involved in the substrate and coenzyme binding of TcFolDH. Considering the extensive involvement of JH in both insects and plants, an in-depth knowledge on the recombinant production of intermediate enzymes of the JH biosynthesis pathway could help provide a potential method for insect control.

Comparative transcriptome analysis of genes involved in the drought stress response of two peanut (Arachis hypogaea L.) varieties

BACKGROUND

The peanut is one of the most important oil crops worldwide. Qualities and yields of peanut can be dramatically diminished by abiotic stresses particularly by drought. Therefore, it would be beneficial to gain a comprehensive understanding on peanut drought-responsive transcriptional regulatory activities, and hopefully to extract critical drought-tolerance-related molecular mechanism from it.

RESULTS

In this study, two peanut Arachis hypogaea L. varieties, NH5 (tolerant) and FH18 (sensitive), which show significantly differential drought tolerance, were screened from 23 main commercial peanut cultivars and used for physiological characterization and transcriptomic analysis. NH5 leaves showed higher water and GSH contents, faster stomatal closure, and lower relative conductivity (REC) than FH18. Under the time-course of drought-treatments 0 h (CK), 4 h (DT1), 8 h (DT2) and 24 h (DT3), the number of down-regulated differential expressed genes (DEGs) increased with the progression of treatments indicating repressive impacts on transcriptomes by drought in both peanut varieties.

CONCLUSIONS

Nevertheless, NH5 maintained more stable transcriptomic dynamics than FH18. Furthermore, annotations of identified DEGs implicate signal transduction, the elimination of reactive oxygen species, and the maintenance of cell osmotic potential which are key drought-tolerance-related pathways. Finally, evidences from the examination of ABA and SA components suggested that the fast stomatal closure in NH5 was likely mediated through SA rather than ABA signaling. In all, these results have provided us a comprehensive overview of peanut drought-responsive transcriptomic changes, which could serve as solid foundation for further identification of the molecular drought-tolerance mechanism in peanut and other oil crops.

Metabolic, Enzymatic Activity, and Transcriptomic Analysis Reveals the Mechanism Underlying the Lack of Characteristic Floral Scent in Apricot Mei Varieties

Apricot mei, a hybrid of Prunus mume and Prunus sibirica, usually has greater cold resistance than P. mume; however, most varieties of Apricot mei lack the characteristic floral scent of P. mume. The volatile and intracellular metabolites, activity levels of key enzymes, and transcriptomes of blooming flowers were comprehensively investigated in five varieties of P. mume. Benzyl acetate and eugenol were determined to be the main components of the P. mume floral scent. However, benzyl benzoate and benzyl alcohol benzoyltransferase activity was detected in only the low-fragrance varieties "Dan Fenghou" and "Yanxing." No benzyl alcohol or benzaldehyde reductase (BAR) activity was detected in the non-fragrant variety "Fenghou." PmBAR1 and PmBAR3 were identified as the key genes responsible for BAR activity. The lack of benzyl alcohol synthesis in the "Fenghou" variety was caused by low activity of PmBAR1-Fen and low expression of PmBAR3. The 60-aa segment at the N-terminus of PmBAR3 was found to play an important role in its enzymatic activity. Correlation tests between floral scent metabolites and the transcriptomes of the five different scented varieties showed that some transcripts associated with hormones, stresses, posttranslational modifications and transporters may also play important regulatory roles in floral scent metabolism in the different varieties.

Tailoring poplar lignin without yield penalty by combining a null and haploinsufficient CINNAMOYL-CoA REDUCTASE2 allele

Lignin causes lignocellulosic biomass recalcitrance to enzymatic hydrolysis. Engineered low-lignin plants have reduced recalcitrance but often exhibit yield penalties, offsetting their gains in fermentable sugar yield. Here, CRISPR/Cas9-generated CCR2(−/*) line 12 poplars have one knockout CCR2 allele while the other contains a 3-bp deletion, resulting in a 114I115A-to-114T conversion in the corresponding protein. Despite having 10% less lignin, CCR2(−/*) line 12 grows normally. On a plant basis, the saccharification efficiency of CCR2(−/*) line 12 is increased by 25–41%, depending on the pretreatment. Analysis of monoallelic CCR2 knockout lines shows that the reduced lignin amount in CCR2(−/*) line 12 is due to the combination of a null and the specific haploinsufficient CCR2 allele. Analysis of another CCR2(−/*) line shows that depending on the specific CCR2 amino-acid change, lignin amount and growth can be affected to different extents. Our findings open up new possibilities for stably fine-tuning residual gene function in planta.

Plants with reduced amounts of lignin typically suffer from dwarfed growth, which offsets their gain in fermentable sugar yield. Here, the authors show that genome-edited poplar lines with a null and a haploinsufficient allele of CINNAMOYL-COA REDUCTASE2 (CCR2) can be obtained that have a reduced lignin level and normal growth.

Comparative temporal metabolomics studies to investigate interspecies variation in three Ocimum species

Ocimum is one of the most revered medicinally useful plants which have various species. Each of the species is distinct in terms of metabolite composition as well as the medicinal property. Some basil types are used more often as an aromatic and flavoring ingredient. It would be informative to know relatedness among the species which though belong to the same genera while exclusively different in terms of metabolic composition and the operating pathways. In the present investigation the similar effort has been made in order to differentiate three commonly occurring Ocimum species having the high medicinal value, these are Ocimum sanctum, O. gratissimum and O. kilimandscharicum. The parameters for the comparative analysis of these three Ocimum species comprised of temporal changes in number leaf trichomes, essential oil composition, phenylpropanoid pathway genes expression and the activity of important enzymes. O. gratissimum was found to be richest in phenylpropanoid accumulation as well as their gene expression when compared to O. sanctum while O. kilimandscharicum was found to be accumulating terpenoid. In order to get an overview of this qualitative and quantitative regulation of terpenes and phenylpropenes, the expression pattern of some important transcription factors involved in secondary metabolism were also studied.

High-Resolution Linkage Map With Allele Dosage Allows the Identification of Regions Governing Complex Traits and Apospory in Guinea Grass (Megathyrsus maximus)

Forage grasses are mainly used in animal feed to fatten cattle and dairy herds, and guinea grass (Megathyrsus maximus) is considered one of the most productive of the tropical forage crops that reproduce by seeds. Due to the recent process of domestication, this species has several genomic complexities, such as autotetraploidy and aposporous apomixis. Consequently, approaches that relate phenotypic and genotypic data are incipient. In this context, we built a linkage map with allele dosage and generated novel information of the genetic architecture of traits that are important for the breeding of M. maximus. From a full-sib progeny, a linkage map containing 858 single nucleotide polymorphism (SNP) markers with allele dosage information expected for an autotetraploid was obtained. The high genetic variability of the progeny allowed us to map 10 quantitative trait loci (QTLs) related to agronomic traits, such as regrowth capacity and total dry matter, and 36 QTLs related to nutritional quality, which were distributed among all homology groups (HGs). Various overlapping regions associated with the quantitative traits suggested QTL hotspots. In addition, we were able to map one locus that controls apospory (apo-locus) in HG II. A total of 55 different gene families involved in cellular metabolism and plant growth were identified from markers adjacent to the QTLs and APOSPORY locus using the Panicum virgatum genome as a reference in comparisons with the genomes of Arabidopsis thaliana and Oryza sativa. Our results provide a better understanding of the genetic basis of reproduction by apomixis and traits important for breeding programs that considerably influence animal productivity as well as the quality of meat and milk.

Discovery of modules involved in the biosynthesis and regulation of maize phenolic compounds

Phenolic compounds are among the most diverse and widespread of specialized plant compounds and underly many important agronomic traits. Our comprehensive analysis of the maize genome unraveled new aspects of the genes involved in phenylpropanoid, monolignol, and flavonoid production in this important crop. Remarkably, just 19 genes accounted for 70 % of the overall mRNA accumulation of these genes across 95 tissues, indicating that these are the main contributors to the flux of phenolic metabolites. Eighty genes with intermediate to low expression play minor and more specialized roles. Remaining genes are likely undergoing loss of function or are expressed in limited cell types. Phylogenetic and expression analyses revealed which members of gene families governing metabolic entry and branch points exhibit duplication, subfunctionalization, or loss of function. Co-expression analysis applied to genes in sequential biosynthetic steps revealed that certain isoforms are highly co-expressed and are candidates for metabolic complexes that ensure metabolite delivery to correct cellular compartments. Co-expression of biosynthesis genes with transcription factors discovered connections that provided candidate components for regulatory modules governing this pathway. Our study provides a comprehensive analysis of maize phenylpropanoid related genes, identifies major pathway contributors, and novel candidate enzymatic and regulatory modules of the metabolic network.

Novel motif is capable of determining CCR and CCR-like proteins based on the divergence of CCRs in plants

Cinnamoyl-coenzyme A reductases (CCRs) have been reported as key enzymes involved in monolignol biosynthesis. In this study, a motif-aware workflow based on a new signature motif effectively distinguished CCRs from CCR-like proteins. The divergence of CCRs and CCR-like sequences in Populus tomentosa Carr, Panicum virgatum L, Oryza sativa L and Selaginella moellendorffii Hieron suggests that NWYCY is not efficient for CCR recognition. The novel motif H202(X)2K205 (CCR-SBM or CCR substrate binding motif) was introduced to distinguish between CCRs and CCR-like proteins. The site-directed mutant R205K in Os(I)CCR-like and H202 in PtoCCR7 resulted in the rescue and loss of activity, respectively, further validating the fact that CCR-SBM is critical for maintaining CCR activity. The molecular docking using feruloyl-cinnamoyl-coenzyme A (CoA) as the ligand and binary PhCCR-NADP structures as receptors indicated an interaction between H202 and K205 with CoA moiety. The genuine CCRs and CCR-like proteins from several angiosperms and gymnosperms were screened using a motif-aware workflow and were validated using a biochemical assay. Our results suggest that the motif-aware workflow is efficient and effective for the identification of CCRs and CCR-like proteins in land plants and can be used as a more accurate way of identifying genuine CCRs among land plants.

Two-step d-ononitol epimerization pathway in Medicago truncatula

Methylated inositol, d-pinitol (3-O-methyl-d-chiro-inositol), is a common constituent in legumes. It is synthesized from myo-inositol in two reactions: the first reaction, catalyzed by myo-inositol-O-methyltransferase (IMT), consists of a transfer of a methyl group from S-adenosylmethionine to myo-inositol with the formation of d-ononitol, while the second reaction, catalyzed by d-ononitol epimerase (OEP), involves epimerization of d-ononitol to d-pinitol. To identify the genes involved in d-pinitol biosynthesis in a model legume Medicago truncatula, we conducted a BLAST search on its genome using soybean IMT cDNA as a query and found putative IMT (MtIMT) gene. Subsequent co-expression analysis performed on publicly available microarray data revealed two potential OEP genes: MtOEPA, encoding an aldo-keto reductase and MtOEPB, encoding a short-chain dehydrogenase. cDNAs of all three genes were cloned and expressed as recombinant proteins in E. coli. In vitro assays confirmed that putative MtIMT enzyme catalyzes methylation of myo-inositol to d-ononitol and showed that MtOEPA enzyme has NAD+ -dependent d-ononitol dehydrogenase activity, while MtOEPB enzyme has NADP+ -dependent d-pinitol dehydrogenase activity. Both enzymes are required for epimerization of d-ononitol to d-pinitol, which occurs in the presence of NAD+ and NADPH. Introduction of MtIMT, MtOEPA, and MtOEPB genes into tobacco plants resulted in production of d-ononitol and d-pinitol in transformants. As this two-step pathway of d-ononitol epimerization is coupled with a transfer of reducing equivalents from NADPH to NAD+ , we speculate that one of the functions of this pathway might be regeneration of NADP+ during drought stress.

Nitrogen Starvation Differentially Influences Transcriptional and Uptake Rate Profiles in Roots of Two Maize Inbred Lines with Different NUE

Nitrogen use efficiency (NUE) of crops is estimated to be less than 50%, with a strong impact on environment and economy. Genotype-dependent ability to cope with N shortage has been only partially explored in maize and, in this context, the comparison of molecular responses of lines with different NUE is of particular interest in order to dissect the key elements underlying NUE. Changes in root transcriptome and NH₄⁺/NO₃^- uptake rates during growth (after 1 and 4 days) without N were studied in high (Lo5) and low (T250) NUE maize inbred lines. Results suggests that only a small set of transcripts were commonly modulated in both lines in response to N starvation. However, in both lines, transcripts linked to anthocyanin biosynthesis and lateral root formation were positively affected. On the contrary, those involved in root elongation were downregulated. The main differences between the two lines reside in the ability to modulate the transcripts involved in the transport, distribution and assimilation of mineral nutrients. With regard to N mineral forms, only the Lo5 line responded to N starvation by increasing the NH₄⁺ fluxes as supported by the upregulation of a transcript putatively involved in its transport.

Enzymatic basis for C-lignin monomer biosynthesis in the seed coat of Cleome hassleriana

C-lignin is a linear polymer of caffeyl alcohol, found in the seed coats of several exotic plant species, with promising properties for generation of carbon fibers and high value chemicals. In the ornamental plant Cleome hassleriana, guaiacyl (G) lignin is deposited in the seed coat for the first 6-12 days after pollination, after which G-lignin deposition ceases and C-lignin accumulates, providing an excellent model system to study C-lignin biosynthesis. We performed RNA sequencing of seed coats harvested at 2-day intervals throughout development. Bioinformatic analysis identified a complete set of lignin biosynthesis genes for Cleome. Transcript analysis coupled with kinetic analysis of recombinant enzymes in Escherichia coli revealed that the switch to C-lignin formation was accompanied by down-regulation of transcripts encoding functional caffeoyl CoA- and caffeic acid 3-O-methyltransferases (CCoAOMT and COMT) and a form of cinnamyl alcohol dehydrogenase (ChCAD4) with preference for coniferaldehyde as substrate, and up-regulation of a form of CAD (ChCAD5) with preference for caffealdehyde. Based on these analyses, blockage of lignin monomer methylation by down-regulation of both O-methyltransferases (OMTs) and methionine synthase (for provision of C1 units) appears to be the major factor in diversion of flux to C-lignin in the Cleome seed coat, although the change in CAD specificity also contributes based on the reduction of C-lignin levels in transgenic Cleome with down-regulation of ChCAD5. Structure modeling and mutational analysis identified amino acid residues important for the preference of ChCAD5 for caffealdehyde.

Down regulation of p-coumarate 3-hydroxylase in petunia uniquely alters the profile of emitted floral volatiles

Petunia × hybrida cv ‘Mitchell Diploid’ floral volatile benzenoid/phenylpropanoid (FVBP) biosynthesis ultimately produces floral volatiles derived sequentially from phenylalanine, cinnamic acid, and p-coumaric acid. In an attempt to better understand biochemical steps after p-coumaric acid production, we cloned and characterized three petunia transcripts with high similarity to p-coumarate 3-hydroxylase (C3H), hydroxycinnamoyl-CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT), and caffeoyl shikimate esterase (CSE). Transcript accumulation of PhC3H and PhHCT was highest in flower limb tissue during open flower stages. PhCSE transcript accumulation was also highest in flower limb tissue, but it was detected earlier at initial flower opening with a bell-shaped distribution pattern. Down regulation of endogenous PhC3H transcript resulted in altered transcript accumulation of many other FVBP network transcripts, a reduction in floral volatiles, and the emission of a novel floral volatile. Down regulation of PhHCT transcript did not have as large of an effect on floral volatiles as was observed for PhC3H down regulation, but eugenol and isoeugenol emissions were significantly reduced on the downstream floral volatiles. Together these results indicate that PhC3H is involved in FVBP biosynthesis and the reduction of PhC3H transcript influences FVBP metabolism at the network level. Additional research is required to illustrate PhHCT and PhCSE functions of petunia.

Exogenous Application of Phytohormones Promotes Growth and Regulates Expression of Wood Formation-Related Genes in Populus simonii × P. nigra

Although phytohormones are known to be important signal molecules involved in wood formation, their roles are still largely unclear. Here, Populus simonii × P. nigra seedlings were treated with different concentrations of exogenous phytohormones, indole-3-acetic acid (IAA), gibberellin (GA₃), and brassinosteroid (BR), and the effects of phytohormones on growth were investigated. Next, 27 genes with known roles in wood formation were selected for qPCR analysis to determine tissue-specificity and timing of responses to phytohormone treatments. Compared to the control, most IAA, GA₃, and BR concentrations significantly increased seedling height. Meanwhile, IAA induced significant seedling stem diameter and cellulose content increases that peaked at 3 and 30 mg·L⁻¹, respectively. Significant increase in cellulose content was also observed in seedlings treated with 100 mg·L⁻¹ GA₃. Neither stem diameter nor cellulose content of seedlings were affected by BR treatment significantly, although slight effects were observed. Anatomical measurements demonstrated improved xylem, but not phloem, development in IAA- and BR-treated seedlings. Most gene expression patterns induced by IAA, GA₃, and BR differed among tissues. Many IAA response genes were also regulated by GA₃, while BR-induced transcription was weaker and slower in Populus than for IAA and GA₃. These results reveal the roles played by phytohormones in plant growth and lay the foundation for exploring molecular regulatory mechanisms of wood formation in Populus.

De novo assembly of Agave sisalana transcriptome in response to drought stress provides insight into the tolerance mechanisms

Agave, monocotyledonous succulent plants, is endemic to arid regions of North America, exhibiting exceptional tolerance to their xeric environments. They employ various strategies to overcome environmental constraints, such as crassulacean acid metabolism, wax depositions, and protective leaf morphology. Genomic resources of Agave species have received little attention irrespective of their cultural, economic and ecological importance, which so far prevented the understanding of the molecular bases underlying their adaptations to the arid environment. In this study, we aimed to elucidate molecular mechanism(s) using transcriptome sequencing of A. sisalana. A de novo approach was applied to assemble paired-end reads. The expression study unveiled 3,095 differentially expressed unigenes between well-irrigated and drought-stressed leaf samples. Gene ontology and KEGG analysis specified a significant number of abiotic stress responsive genes and pathways involved in processes like hormonal responses, antioxidant activity, response to stress stimuli, wax biosynthesis, and ROS metabolism. We also identified transcripts belonging to several families harboring important drought-responsive genes. Our study provides the first insight into the genomic structure of A. sisalana underlying adaptations to drought stress, thus providing diverse genetic resources for drought tolerance breeding research.

Proteome Profile of American Hybrid Grape cv. Blanc du Bois during Ripening Reveals Proteins Associated with Flavor Volatiles and Ethylene Production

The study of key control points in ripening is essential to improve grape wine quality. Molecular basis of ripening is still far from being understood from the Pierce's disease (PD)-tolerant grapes predominantly grown in the southeastern United States. To identify proteins expressed during Blanc du Bois grape berry green and ripening stages, proteome analysis from five different stages revealed 1091, 1131, 1078, 1042, and 1066 proteins. Differential expression analysis revealed 551 common proteins across different stages of maturity that are involved in various biochemical and metabolic pathways. The proteins identified were associated with phenylpropanoids, isoquinoline alkaloids, fatty acids, unsaturated fatty acids, and furanones. Our data provide the first step to understand the complex biochemical changes during ripening of PD-tolerant American hybrid grapes that are popular for their aroma and flavor profile in the southeastern United States. Proteomics data are deposited to the ProteomeXchange PXD004157.

Overexpression of Artemisia annua Cinnamyl Alcohol Dehydrogenase Increases Lignin and Coumarin and Reduces Artemisinin and Other Sesquiterpenes

Artemisia annua is the only medicinal crop that produces artemisinin for malarial treatment. Herein, we describe the cloning of a cinnamyl alcohol dehydrogenase (AaCAD) from an inbred self-pollinating (SP) A. annua cultivar and its effects on lignin and artemisinin production. A recombinant AaCAD was purified via heterogeneous expression. Enzyme assays showed that the recombinant AaCAD converted p-coumaryl, coniferyl, and sinapyl aldehydes to their corresponding alcohols, which are key intermediates involved in the biosynthesis of lignin. Km, Vmax, and Vmax/Km values were calculated for all three substrates. To characterize its function in planta, AaCAD was overexpressed in SP plants. Quantification using acetyl bromide (AcBr) showed significantly higher lignin contents in transgenics compared with wild-type (WT) plants. Moreover, GC-MS-based profiling revealed a significant increase in coumarin contents in transgenic plants. By contrast, HPLC-MS analysis showed significantly reduced artemisinin contents in transgenics compared with WT plants. Furthermore, GC-MS analysis revealed a decrease in the contents of arteannuin B and six other sesquiterpenes in transgenic plants. Confocal microscopy analysis showed the cytosolic localization of AaCAD. These data demonstrate that AaCAD plays a dual pathway function in the cytosol, in which it positively enhances lignin formation but negatively controls artemisinin formation. Based on these data, crosstalk between these two pathways mediated by AaCAD catalysis is discussed to understand the metabolic control of artemisinin biosynthesis in plants for high production.

Characterization and analysis of CCR and CAD gene families at the whole-genome level for lignin synthesis of stone cells in pear (Pyrus bretschneideri) fruit

The content of stone cells has significant effects on the flavour and quality of pear fruit. Previous research suggested that lignin deposition is closely related to stone cell formation. In the lignin biosynthetic pathway, cinnamoyl-CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD), dehydrogenase/reductase family members, catalyse the last two steps in monolignol synthesis. However, there is little knowledge of the characteristics of the CCR and CAD families in pear and their involvement in lignin synthesis of stone cells. In this study, 31 CCRs and 26 CADs were identified in the pear genome. Phylogenetic trees for CCRs and CADs were constructed; key amino acid residues were analysed, and three-dimensional structures were predicted. Using quantitative real-time polymerase chain reaction (qRT-PCR), PbCAD2, PbCCR1, -2 and -3 were identified as participating in lignin synthesis of stone cells in pear fruit. Subcellular localization analysis showed that the expressed proteins (PbCAD2, PbCCR1, -2 and -3) are found in the cytoplasm or at the cell membrane. These results reveal the evolutionary features of the CCR and CAD families in pear as well as the genes responsible for regulation of lignin synthesis and stone cell development in pear fruit.

Phenylpropanoid Scent Compounds in Petunia x hybrida Are Glycosylated and Accumulate in Vacuoles

Floral scent has been studied extensively in the model plant Petunia. However, little is known about the intracellular fate of scent compounds. Here, we characterize the glycosylation of phenylpropanoid scent compounds in Petunia x hybrida. This modification reduces scent compounds' volatility, reactivity, and autotoxicity while increasing their water-solubility. Gas chromatography-mass spectrometry (GC-MS) analyses revealed that flowers of petunia cultivars accumulate substantial amounts of glycosylated scent compounds and that their increasing level parallels flower development. In contrast to the pool of accumulated aglycones, which drops considerably at the beginning of the light period, the collective pool of glycosides starts to increase at that time and does not decrease thereafter. The glycoside pool is dynamic and is generated or catabolized during peak scent emission, as inferred from phenylalanine isotope-feeding experiments. Using several approaches, we show that phenylpropanoid scent compounds are stored as glycosides in the vacuoles of petal cells: ectopic expression of Aspergillus niger β-glucosidase-1 targeted to the vacuole resulted in decreased glycoside accumulation; GC-MS analysis of intact vacuoles isolated from petal protoplasts revealed the presence of glycosylated scent compounds. Accumulation of glycosides in the vacuoles seems to be a common mechanism for phenylpropanoid metabolites.

Two distinct cinnamoyl-CoA reductases in Selaginella moellendorffii offer insight into the divergence of CCRs in plants

Two distinct cinnamoyl-coenzyme A reductases (CCRs) from Selaginella moellendorffii were evaluated, and of these, SmCCR2-1, which has both distinct sequence motifs and catalytic properties, was clustered into a new CCR subgroup. Cinnamoyl-coenzyme A reductases (CCRs) have been reported in many land plants to have critical functions in monolignol biosynthesis. In this study, we performed a genome-wide screen and obtained two distinct SmCCRs from S. moellendorffii. Phylogenetic analysis indicated that SmCCR2 (both SmCCR2-1 and 2-2) and SmCCR3 together with PpaCCR belong to a distinct subgroup of genuine CCRs with variations in the NAD(P)H-binding motif. Enzymatic assays showed detectable activity by both SmCCR1 and SmCCR2-1 toward four hydroxycinnamoyl-CoA esters. SmCCR1, which clustered with reported CCRs from angiosperms and gymnosperms, exhibited specificity toward feruloyl-CoA, while SmCCR2-1 showed a preference for sinapoyl-CoA. Interestingly, the reaction temperature profiles for SmCCR1 and SmCCR2-1 are complementary. Homology models and molecular simulations suggest that the variations in NADPH-binding motifs, especially R(X)₆K instead of R(X)₅K, affect the NADP⁺ conformation. Notably, the signature motif NWYCY was replaced with NGYCL in SmCCR1 and with EWYCL in SmCCR2-1, while the signature residues H202 and R253, reported in a previous study, were conserved in SmCCR1 and SmCCR2-1 but varied in SmCCR-like genes. It is likely that NWYCY is not a reliable signature for CCRs in plants. The detectable activity of site-direct mutant S123T of SmCCR1 suggested that S123 which consists of catalytic triad is changeable. Possible evolution process for the emergence of two subgroups of genuine CCRs was also revealed. Altogether, these findings revise our understanding of CCRs with regard to divergence and active sites.

Three steps in one pot: biosynthesis of 4-hydroxycinnamyl alcohols using immobilized whole cells of two genetically engineered Escherichia coli strains

Background

4-Hydroxycinnamyl alcohols are a class of natural plant secondary metabolites that include p-coumaryl alcohol, caffeyl alcohol, coniferyl alcohol and sinapyl alcohol, and have physiological, ecological and biomedical significance. While it is necessary to investigate the biological pathways and economic value of these alcohols, research is hindered because of their limited availability and high cost. Traditionally, these alcohols are obtained by chemical synthesis and plant extraction. However, synthesis by biotransformation with immobilized microorganisms is of great interest because it is environmentally friendly and offers high stability and regenerable cofactors. Therefore, we produced 4-hydroxycinnamyl alcohols using immobilized whole cells of engineered Escherichia coli as the biocatalyst.

Results

In this study, we used the recombinant E. coli strain, M15–4CL1–CCR, expressing the fusion protein 4-coumaric acid: coenzyme A ligase and the cinnamoyl coenzyme A reductase and a recombinant E. coli strain, M15–CAD, expressing cinnamyl alcohol dehydrogenase from Populus tomentosa (P. tomentosa). High performance liquid chromatography and mass spectrometry showed that the immobilized whole cells of the two recombinant E. coli strains could effectively convert the phenylpropanoic acids to their corresponding 4-hydroxycinnamyl alcohols. Further, the optimum buffer pH and the reaction temperature were pH 7.0 and 30 °C. Under these conditions, the molar yield of the p-coumaryl alcohol, the caffeyl alcohol and the coniferyl alcohol was around 58, 24 and 60%, respectively. Moreover, the highly sensitive and selective HPLC–PDA–ESI–MSn method used in this study could be applied to the identification and quantification of these aromatic polymers.

Conclusions

We have developed a dual-cell immobilization system for the production of 4-hydroxycinnamyl alcohols from inexpensive phenylpropanoic acids. This biotransformation method is both simple and environmental-friendly, which is promising for the practical and cost effective synthesis of natural products.Graphical abstract