De novo transcriptome characterization of Lilium 'Sorbonne' and key enzymes related to the flavonoid biosynthesis

Full-Length Transcriptome Characterization and Functional Analysis of Pathogenesis-Related Proteins in Lilium Oriental Hybrid 'Sorbonne' Infected with Botrytis elliptica

Gray mold (Botrytis elliptica) causes a deleterious fungal disease that decreases the ornamental value and yield of lilies. Lilium oriental hybrid 'Sorbonne' is a variety that is resistant to gray mold. Understanding the mechanism of resistance against B. elliptica infection in 'Sorbonne' can provide a basis for the genetic improvement in lily plants. In this study, a PacBio Sequel II system was used to sequence the full-length transcriptome of Lilium 'Sorbonne' after inoculation with B. elliptica. A total of 46.64 Gb subreads and 19,102 isoforms with an average length of 1598 bp were obtained. A prediction analysis revealed 263 lncRNAs, and 805 transcription factors, 4478 simple sequence repeats, and 17,752 coding sequences were identified. Pathogenesis-related proteins (PR), which may play important roles in resistance against B. elliptica infection, were identified based on the full-length transcriptome data and previously obtained second-generation transcriptome data. Nine non-redundant potential LhSorPR proteins were identified and assigned to two groups that were composed of two LhSorPR4 and seven LhSorPR10 proteins based on their genetic relatedness. The real-time quantitative reverse transcription PCR (qRT-PCR) results showed that the patterns of expression of nine differentially expressed PR genes under B. elliptica stress were basically consistent with the results of transcriptome sequencing. The pattern of expression of LhSorPR4s and LhSorPR10s genes in different tissues was analyzed, and the expression of each gene varied. Furthermore, we verified the function of LhSorPR4-2 gene in Lilium. The expression of LhSorPR4-2 was induced by phytohormones such as methyl jasmonate, salicylic acid, and ethephon. Moreover, the promoter region of LhSorPR4-2 was characterized by several functional domains associated with phytohormones and stress response. The overexpression of LhSorPR4-2 gene in 'Sorbonne' increased the resistance of the lily plant to B. elliptica and correlated with high chitinase activity. This study provides a full-length transcript database and functionally analyzed the resistance of PR gene to B. elliptica in Lilium, thereby introducing the candidate gene LhSorPR4-2 to breed resistance in Lilium.

Ethylene Response Factor LlERF110 Mediates Heat Stress Response via Regulation of LlHsfA3A Expression and Interaction with LlHsfA2 in Lilies (Lilium longiflorum)

Heat stress seriously affects the quality of cut lily flowers. The ethylene response factors (ERFs) participate in heat stress response in many plants. In this study, heat treatment increased the production of ethylene in lily leaves, and exogenous ethylene treatment enhanced the heat resistance of lilies. LlERF110, an important transcription factor in the ethylene signaling pathway, was found in the high-temperature transcriptome. The coding region of LlERF110 (969 bp) encodes 322 amino acids and LlERF110 contains an AP2/ERF typical domain belonging to the ERF subfamily group X. LlERF110 was induced by ethylene and was expressed constitutively in all tissues. LlERF110 is localized in the nucleus and has transactivation activity. Virus-induced gene silencing of LlERF110 in lilies reduced the basal thermotolerance phenotypes and significantly decreased the expression of genes involved in the HSF-HSP pathway, such as LlHsfA2, LlHsfA3A, and LlHsfA5, which may activate other heat stress response genes; and LlHsp17.6 and LlHsp22, which may protect proteins under heat stress. LlERF110 could directly bind to the promoter of LlHsfA3A and activate its expression according to the yeast one hybrid and dual-luciferase reporter assays. LlERF110 interacts with LlHsfA2 in the nucleus according to BiFC and the yeast two-hybrid assays. In conclusion, these results indicate that LlERF110 plays an important role in the basal thermotolerance of lilies via regulation of the HSF-HSP pathway, which could be the junction of the heat stress response pathway and the ethylene signaling pathway.

Comparative transcriptome and metabolome analyses identified the mode of sucrose degradation as a metabolic marker for early vegetative propagation in bulbs of Lycoris

Vegetative propagation (VP) is an important practice for production in many horticultural plants. Sugar supply constitutes the basis of VP in bulb flowers, but the underlying molecular basis remains elusive. By performing a combined sequencing technologies coupled with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry approach for metabolic analyses, we compared two Lycoris species with contrasting regeneration rates: high-regeneration Lycoris sprengeri and low-regeneration Lycoris aurea. A comprehensive multi-omics analyses identified both expected processes involving carbohydrate metabolism and transcription factor networks, as well as the metabolic characteristics for each developmental stage. A higher abundance of the differentially expressed genes including those encoding ethylene responsive factors was detected at bulblet initiation stage compared to the late stage of bulblet development. High hexose-to-sucrose ratio correlated to bulblet formation across all the species examined, indicating its role in the VP process in Lycoris bulb. Importantly, a clear difference between cell wall invertase (CWIN)-catalyzed sucrose unloading in high-regeneration species and the sucrose synthase-catalyzed pathway in low-regeneration species was observed at the bulblet initiation stage, which was supported by findings from carboxyfluorescein tracing and quantitative real-time PCR analyses. Collectively, the findings indicate a sugar-mediated model of the regulation of VP in which high CWIN expression or activity may promote bulblet initiation via enhancing apoplasmic unloading of sucrose or sugar signals, whereas the subsequent high ratio of hexose-to-sucrose likely supports cell division characterized in the next phase of bulblet formation.

The Heat Stress Transcription Factor LlHsfA4 Enhanced Basic Thermotolerance through Regulating ROS Metabolism in Lilies (Lilium Longiflorum)

Heat stress severely affects the annual agricultural production. Heat stress transcription factors (HSFs) represent a critical regulatory juncture in the heat stress response (HSR) of plants. The HsfA1-dependent pathway has been explored well, but the regulatory mechanism of the HsfA1-independent pathway is still under-investigated. In the present research, HsfA4, an important gene of the HsfA1-independent pathway, was isolated from lilies (Lilium longiflorum) using the RACE method, which encodes 435 amino acids. LlHsfA4 contains a typical domain of HSFs and belongs to the HSF A4 family, according to homology comparisons and phylogenetic analysis. LlHsfA4 was mainly expressed in leaves and was induced by heat stress and H₂O₂ using qRT-PCR and GUS staining in transgenic Arabidopsis. LlHsfA4 had transactivation activity and was located in the nucleus and cytoplasm through a yeast one hybrid system and through transient expression in lily protoplasts. Over expressing LlHsfA4 in Arabidopsis enhanced its basic thermotolerance, but acquired thermotolerance was not achieved. Further research found that heat stress could increase H₂O₂ content in lily leaves and reduced H₂O₂ accumulation in transgenic plants, which was consistent with the up-regulation of HSR downstream genes such as Heat stress proteins (HSPs), Galactinol synthase1 (GolS1), WRKY DNA binding protein 30 (WRKY30), Zinc finger of Arabidopsis thaliana 6 (ZAT6) and the ROS-scavenging enzyme Ascorbate peroxidase 2 (APX2). In conclusion, these results indicate that LlHsfA4 plays important roles in heat stress response through regulating the ROS metabolism in lilies.

Metabolic and Transcriptomic Profiling of Lilium Leaves Infected With Botrytis elliptica Reveals Different Stages of Plant Defense Mechanisms

Botrytis elliptica, the causal agent of gray mold disease, poses a major threat to commercial Lilium production, limiting its ornamental value and yield. The molecular and metabolic regulation mechanisms of Lilium's defense response to B. elliptica infection have not been completely elucidated. Here, we performed transcriptomic and metabolomic analyses of B. elliptica resistant Lilium oriental hybrid "Sorbonne" to understand the molecular basis of gray mold disease resistance in gray mold disease. A total of 115 differentially accumulated metabolites (DAMs) were detected by comparing the different temporal stages of pathogen infection. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed the differentially expressed genes (DEGs) and DAMs were enriched in the phenylpropanoid and flavonoid pathways at all stages of infection, demonstrating the prominence of these pathways in the defense response of "Sorbonne" to B. elliptica. Network analysis revealed high interconnectivity of the induced defense response. Furthermore, time-course analysis of the transcriptome and a weighted gene coexpression network analysis (WGCNA) led to the identification of a number of hub genes at different stages, revealing that jasmonic acid (JA), salicylic acid (SA), brassinolide (BR), and calcium ions (Ca2+) play a crucial role in the response of "Sorbonne" to fungal infection. Our work provides a comprehensive perspective on the defense response of Lilium to B. elliptica infection, along with a potential transcriptional regulatory network underlying the defense response, thereby offering gene candidates for resistance breeding and metabolic engineering of Lilium.

Transcriptome profiling to identify tepal cell enlargement and pigmentation genes and the function of LtEXLB1 in Lilium tsingtauense

To understand the molecular mechanism underlying tepal development and pigmentation in Lilium tsingtauense Gilg, we performed whole-transcriptome profiles from closed buds at the greenish tepal stage (CBS), the full-bloom with un-horizontal tepal stage (UFS), and the completely opened bud with reflected tepal stage (RFS) of L. tsingtauense. More than 95699 transcripts were generated using a de novo assembly approach. Gene ontology and pathway analysis of the assembled transcripts revealed carbon metabolism is involved in tepal development and pigmentation. In total, 8171 differentially expression genes (DEGs) in three tepal stages were identified. Among these DEGs, ~994 genes putatively encoded transcription factors (TFs), whereas 693 putatively encoded protein kinases. Regarding hormone pathways, 51 DEGs involved in auxin biosynthesis and signalling and 10 DEGs involved in ethylene biosynthesis and signalling. We also isolated seven LtEXPANSINs, including four EXPAs, one EXPB, one EXLA and one EXLB. LtEXLB1 (GenBank: MN856627) was expressed at higher levels in UFS and RFS, compared with CBS. Silencing LtEXLB1 in leaf discs and tepals by virus-induced gene silencing significantly decreased cell expansion under rehydration conditions. Further analysis revealed that more cell numbers were existed in the abaxial and adaxial subepidermis in the silenced LtEXLB1 samples. As the first transcriptome of L. tsingtauense, the unigenes are a valuable resource for future studies on tepal development, and LtEXLB1 functions in cell expansion.

Change in Sucrose Cleavage Pattern and Rapid Starch Accumulation Govern Lily Shoot-to-Bulblet Transition in vitro

In bulb crops, bulbing is a key progress in micropropagation and is the feature that most distinguishes bulbous crops from other plants. Generally, bulbing involves a shoot-to-bulblet transition; however, the underlying mechanism remains elusive. We explored this process by tracking the shoot-to-bulblet transition under different culture conditions. Rapid starch accumulation occurred at 15 days after transplanting (DAT) in the bulblet-inducing treatments as confirmed via histological observations and the significant elevation of starch synthesis related-gene transcription, including LohAGPS, LohAGPL, LohGBSS, LohSS, and LohSBE. However, for shoots that did not transition to bulblets and maintained the shoot status, much higher soluble sugars were detected. Interestingly, we observed a clear shift from invertase-catalyzed to sucrose synthase-catalyzed sucrose cleavage pattern based on the differential expression of LohCWIN and LohSuSy during the key transition stage (prior to and after bulbing at 0-15 DAT). Shoots that transitioned into bulblets showed significantly higher LohSuSy expression, especially LohSuSy4 expression, than shoots that did not transition. A symplastic phloem unloading pathway at the bulblet emergence stage (15 DAT) was verified via the 6(5)-carboxyfluorescein diacetate fluorescent tracer. We propose that starch is the fundamental compound in the shoot-to-bulblet transition and that starch synthesis is likely triggered by the switch from apoplastic to symplastic sucrose unloading, which may be related to sucrose depletion. Furthermore, this study is the first to provide a complete inventory of the genes involved in starch metabolism based on our transcriptome data. Two of these genes, LohAGPS1.2b and LohSSIIId, were verified by rapid amplification of cDNA ends cloning, and these data will provide additional support for Lilium research since whole genome is currently lacking.

Full-length transcriptome analysis and identification of genes involved in asarinin and aristolochic acid biosynthesis in medicinal plant Asarum sieboldii

Asarum sieboldii, a well-known traditional Chinese medicinal herb, is used for curing inflammation and ache. It contains both the bioactive ingredient asarinin and the toxic compound aristolochic acid. To address further breeding demand, genes involved in the biosynthetic pathways of asarinin and aristolochic acid should be explored. Therefore, the full-length transcriptome of A. sieboldii was sequenced using PacBio Iso-Seq to determine the candidate transcripts that encode the biosynthetic enzymes of asarinin and aristolochic acid. In this study, 63 023 full-length transcripts were generated with an average length of 1371 bp from roots, stems, and leaves, of which 49 593 transcripts (78.69%) were annotated against public databases. Furthermore, 555 alternative splicing (AS) events, 10 869 long noncoding RNAs (lncRNAs) as well as their 11 291 target genes, and 17 909 simple sequence repeats (SSRs) were identified. The data also revealed 97 candidate transcripts related to asarinin metabolism, of which six novel genes that encoded enzymes involved in asarinin biosynthesis were initially reported. In addition, 56 transcripts related to aristolochic acid biosynthesis were also identified, including CYP81B. In summary, these transcriptome data provide a useful resource to study gene function and genetic engineering in A. sieboldii.

Differential expression after UV-B radiation and characterization of chalcone synthase from the Patagonian hairgrass Deschampsia antarctica

Deschampsiaantarctica inhabits the maritime territory of Antarctica and South Patagonia. It grows under very harsh environmental conditions. The survival of this species in low freezing temperatures and under high levels of UV-B radiation may constitute some of the most remarkable adaptive plant responses and suggests that this plant possesses genes associated with cold and UV tolerance. Frequently, increased levels of flavonoids have been linked to highly UV-B irradiated plants. Studies examining the biosynthesis of flavonoids in D. antarctica may provide clues to its success in this extreme environment. In this study, we characterized the family of genes encoding chalcone synthase, a key enzyme of the flavonoid biosynthetic pathway. DaCHS was cloned, sequenced and characterized by using software tools. CHS contains two domains, the N-terminal domain ranges from amino acid 8 to 231 and the C-terminal domain ranges from amino acid 241 to 391. Sequence analysis of the three family members revealed a high degree of identity after comparison with other monocotyledons such as Oryza sativa L., Zea mays L. and Hordeum vulgare L. According to these results, DaCHS can be grouped together with H. vulgare CHS1 in the same branch. The phylogenetic tree was built using MEGA software and the neighbour join method with 1000 bootstrap replicates. A model of DaCHS was constructed by way of structural tools and key amino acid residues were identified at the active motif site.

Transcriptome Sequencing Analysis Provides Insights Into the Response to Fusarium oxysporum in Lilium pumilum

Lily basal rot, caused by Fusarium oxysporum f. sp. lilii, is one of the most serious diseases of lily. Although the lily germplasm which is resistant to F. oxysporum has been used in disease-resistant breeding, few studies on its molecular mechanism of disease resistance have been reported. To comprehensively study the mechanism of resistance to F. oxysporum, transcriptome sequencings of root tissues from Lilium pumilum inoculated with F. oxysporum or sterile water for 6, 12, or 24 h were performed. A total of 50 GB of data were obtained from the transcriptome sequencings of the 6 L. pumilum samples, and 217 098 Unigenes were obtained after the de novo assembly, of which 38.36% Unigenes were annotated. The sequencing results showed that the numbers of differentially expressed genes at 6, 12, and 24 h after inoculation compared with the control were 111, 254, and 2500, respectively. The functional enrichment analysis of the differentially expressed genes showed that several pathways were involved in responses of L. pumilum, mainly including starch and sucrose metabolism, glycolysis/gluconeogenesis, phenylpropanoid biosynthesis, plant hormone signal transduction, flavonoid biosynthesis, vitamin B6 (VB6) biosynthesis, acid biosynthesis, proteasome, and ribosome. Transcription factor analysis revealed that the WRKY and ERF families played important roles in responses of L. pumilum to F. oxysporum. The results of this study elucidate the molecular responses to F. oxysporum in lily and lay a theoretical foundation for improving lily breeding and strategies for lily basal rot resistance.

Comparative Transcriptome Analysis of Celery Leaf Blades Identified an R2R3-MYB Transcription Factor that Regulates Apigenin Metabolism

Apigenin has been proven to possess many pharmacological properties, but the mechanism of regulation of apigenin biosynthesis in plants remains unclear. Apigenin is the main flavonoid in celery and is mainly accumulated in the middle stage of leaf blade development. In this study, comparative transcriptomic analysis revealed a large number of structural genes and transcription factor genes that may be involved in the apigenin metabolic pathway. On the basis of the apigenin content in different celery accessions, an R2R3-MYB transcription factor gene, named AgMYB1, was isolated from the high apigenin celery accession C014. Bioinformatics analysis indicated that AgMYB1 may be involved in flavonoid metabolism. AgMYB1 expression showed a positive relation with the expression of the apigenin accumulation marker gene FNSI and with the apigenin content in different celery tissues. Moreover, overexpression and antisense expression of AgMYB1 in transgenic celery plants significantly increased and reduced the expression of apigenin biosynthetic genes and the apigenin content, respectively. These findings suggest that AgMYB1 is involved in positive regulation of apigenin metabolism in celery.

Cloning and expression analysis of LoCCD8 during IAA-induced bulbils outgrowth in lily (Oriental Hybrid 'Sorbonne')

Aerial bulbils, which resemble tiny bulbs, develop from axillary buds and facilitate rapid propagation of Lilium. In most species of lily, bulbils are perpetually dormant and little is known about induction of these vegetative structures. Herein, we proposed that strigolactones (SLs) may regulate the induction of bulbils in Lilium. We tested this hypothesis by isolating and investigating the expression patterns of 2 copies of the carotenoid cleavage dioxygenase8 (CCD8) gene in lily-LoCCD8a and LoCCD8b-with regard to biosynthesis of SLs. Expression analyses revealed that LoCCD8a principally is expressed during vegetative growth, whereas LoCCD8b mainly is expressed during reproductive growth. The maximum quantity of LoCCD8a transcripts was observed in the basal plate in most developmental stages, which suggests that SLs may originate from underground parts, especially the basal plate, and move upward. The effects of treatments with indole-3-acetic acid or SL analog (GR24) on outgrowth of bulbils and expression of LoCCD8 genes suggested that SLs function downstream of auxin to inhibit the outgrowth of bulbil. The expression patterns of LoCCD8a and LoCCD8b at sprouting and bulblet weighting stages also implied that SLs may function in nutrient redistribution. Our findings are expected to promote the utilization of bulbils as vegetative propagules for commercial practice.

Integrating Transcriptomic and GC-MS Metabolomic Analysis to Characterize Color and Aroma Formation during Tepal Development in Lycoris longituba

Lycoris longituba, belonging to the Amaryllidaceae family, is a perennial bulb bearing flowers with diverse colors and fragrance. Selection of cultivars with excellent colored and scented flowers has always been the breeding aim for ornamental plants. However, the molecular mechanisms underlying color fading and aroma production during flower expansion in L. longituba remain unclear. Therefore, to systematically investigate these important biological phenomena, the tepals of L. longituba from different developmental stages were used to screen and analyze the metabolic components and relevant genes. Utilizing the Illumina platform, a total of 144,922 unigenes were obtained from the RNA-Seq libraries. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated that the phenylpropanoid biosynthesis and flavonoid biosynthesis pathways might play important roles during color and aroma changes. Metabolomic analysis identified 29 volatile organic components (VOCs) from different developmental stages of L. longituba tepals, and orthogonal partial least-squares discriminate analysis (OPLS-DA) revealed that trans-β-ocimene—a terpene—was the most important aroma compound. Meanwhile, we found the content of anthocyanin was significantly reduced during the tepal color fading process. Then, we identified two dihydroflavonol-4-reductase (DFR) and three terpene synthase (TPS) genes, for which expression changes coincided with the production patterns of anthocyanins and trans-β-ocimene, respectively. Furthermore, a number of MYB and bHLH transcription factors (TFs) which might be involved in color- and aroma-formation were also identified in L. longituba tepal transcriptomes. Taken together, this is the first comprehensive report of the color and fragrance in tepals of L. longituba and these results could be helpful in understanding these characteristics and their regulation networks.

Transcriptome changes in the phenylpropanoid pathway in senescing leaves of Toona sinensis

Toona sinensis is a deciduous tree native to eastern and southeastern Asia that has important culinary and cultural values. To expand current knowledge of the transcriptome and functional genomics in this species, a de novo transcriptome sequence analysis of young and mature leaf tissues of T. sinensis was performed using the Illumina platform. Over 8.1 Gb of data were generated, assembled into 64,541 unigenes, and annotated with known biological functions. Proteins involved in primary metabolite biosynthesis were identified based on similarities to known proteins, including some related to biosynthesis of carbohydrates, amino acids, lipids, and energy. Analysis of unigenes differentially expressed between young and mature leaves (transcriptomic libraries 'YL' and 'ML', respectively) showed that the KEGG pathways of phenylpropanoid, naringenin, lignin, cutin, suberin, and wax biosynthesis were significantly enriched in mature leaves. These results not only expand knowledge of transcriptome characteristics for this valuable species, but also provide a useful transcriptomic dataset to accelerate the researches on its metabolic mechanisms and functional genomics. This study can also further the understanding of unique aromatic metabolism and Chinese medicinal properties of T. sinensis.

Construction of a high-density genetic map: genotyping by sequencing (GBS) to map purple seed coat color (Psc) in hulless barley

Background

Colored hulless barley are more suitable in food processing compared to normal (yellow) varieties because it is rich in bioactive compounds and produces higher extraction pearling fractions. Therefore, seed coat color is an important agronomic trait for the breeding and study of hulless barley.

Results

Genotyping-by-sequencing single-nucleotide polymorphism (GBS-SNP) analysis of a doubled haploid (DH) mapping population (Nierumuzha × Kunlun10) was conducted to map the purple seed coat color genes (Psc). A high-density genetic map of hulless barley was constructed, which contains 3662 efficient SNP markers with 1129 bin markers. Seven linkage groups were resolved, which had a total length of 645.56 cM. Chromosome length ranged from 60.21 cM to 127.21 cM, with average marker density of 0.57 cM. A total of five loci accounting for 3.79% to 23.86% of the observed phenotypic variation for Psc were detected using this high-density map. Five structural candidate genes (F3’M, HID, UF3GT, UFGT and 5MAT) and one regulatory factor (Ant1) related to flavonoid or anthocyanin biosynthesis were identified..

Conclusions

Five structural candidate genes and one regulatory factor related to flavonoid or anthocyanin biosynthesis have been identified using a high-density genetic map of hulless barley. This study lays the foundation for map-based cloning of Psc but provides a valuable tool for studying marker-trait associations and its application to marker-assisted breeding of hulless barley.

Electronic supplementary material

The online version of this article (10.1186/s41065-018-0072-6) contains supplementary material, which is available to authorized users.

De Novo Transcriptome Sequencing of the Deep-Sea-Derived Fungus Dichotomomyces cejpii and Analysis of Gliotoxin Biosynthesis Genes

Gliotoxin, produced by fungi, is an epipolythiodioxopiperazine (ETP) toxin with bioactivities such as anti-liver fibrosis, antitumor, antifungus, antivirus, antioxidation, and immunoregulation. Recently, cytotoxic gliotoxins were isolated from a deep-sea-derived fungus, Dichotomomyces cejpii. However, the biosynthetic pathway for gliotoxins in D. cejpii remains unclear. In this study, the transcriptome of D. cejpii was sequenced using an Illumina Hiseq 2000. A total of 19,125 unigenes for D. cejpii were obtained from 9.73 GB of clean reads. Ten genes related to gliotoxin biosynthesis were annotated. The expression levels of gliotoxin-related genes were detected through quantitative real-time polymerase chain reaction (qRT-PCR). The GliG gene, encoding a glutathione S-transferase (DC-GST); GliI, encoding an aminotransferase (DC-AI); and GliO, encoding an aldehyde reductase (DC-AR), were cloned and expressed, purified, and characterized. The results suggested the important roles of DC-GST, DC-AT, and DC-AR in the biosynthesis of gliotoxins. Our study on the genes related to gliotoxin biosynthesis establishes a molecular foundation for the wider application of gliotoxins from D. cejpii in the biomedical industry in the future.

Two-dimensional analysis provides molecular insight into flower scent of Lilium 'Siberia'

Lily is a popular flower around the world not only because of its elegant appearance, but also due to its appealing scent. Little is known about the regulation of the volatile compound biosynthesis in lily flower scent. Here, we conducted an approach combining two-dimensional analysis and weighted gene co-expression network analysis (WGCNA) to explore candidate genes regulating flower scent production. In the approach, changes of flower volatile emissions and corresponding gene expression profiles at four flower developmental stages and four circadian times were both captured by GC-MS and RNA-seq methods. By overlapping differentially-expressed genes (DEGs) that responded to flower scent changes in flower development and circadian rhythm, 3,426 DEGs were initially identified to be candidates for flower scent production, of which 1,270 were predicted as transcriptional factors (TFs). The DEGs were further correlated to individual flower volatiles by WGCNA. Finally, 37, 41 and 90 genes were identified as candidate TFs likely regulating terpenoids, phenylpropanoids and fatty acid derivatives productions, respectively. Moreover, by WGCNA several genes related to auxin, gibberellins and ABC transporter were revealed to be responsible for flower scent production. Thus, this strategy provides an important foundation for future studies on the molecular mechanisms involved in floral scent production.

Identification of differentially expressed genes in flower, leaf and bulb scale of Lilium oriental hybrid 'Sorbonne' and putative control network for scent genes

BACKGROUND

Lily is an economically important plant, with leaves and bulbs consisting of overlapping scales, large ornamental flowers and a very large genome. Although it is recognized that flowers and bulb scales are modified leaves, very little is known about the genetic control and biochemical differentiation underlying lily organogenesis and development. Here we examined the differentially expressed genes in flower, leaf and scale of lily, using RNA-sequencing, and identified organ-specific genes, including transcription factors, genes involved in photosynthesis in leaves, carbohydrate metabolism in bulb scales and scent and color production in flowers.

RESULTS

Over 11Gb data were obtained and 2685, 2296, and 1709 differentially expressed genes were identified in the three organs, with 581, 662 and 977 unique DEGs in F-vs-S, L-vs-S and L-vs-F comparisons. By functional enrichment analysis, genes likely to be involved in biosynthetic pathways leading to floral scent production, such as 1-deoxy-D-xylulose-5-phosphate synthase (DXS), 3-ketoacyl-CoA thiolase (KAT), hydroperoxide lyase (HPL), geranylgeranyl pyrophosphate (GGPP) 4-hydroxy-3-methylbut-2-en-1-yl diphosphate (HDS) and terpene synthase (TPS), and floral color genes, such as dihydroflavonol 4-reductase (DFR), chalcone synthase (CHS), chalcone isomerase (CHI), flavonol synthase (FLS) were identified. Distinct groups of genes that participate in starch and sucrose metabolism, such as sucrose synthase (SS), invertase (INV), sucrose phosphate synthase (SPS), starch synthase (SSS), starch branching enzyme (SBE), ADP-glucose pyrophosphorylase (AGP) andβ-amylase (BAM) and photosynthesis genes (Psa, Psb, Pet and ATP) were also identified. The expression of six floral fragrance-related DGEs showed agreement between qRT-PCR results and RPKM values, confirming the value of the data obtained by RNA-seq. We obtained the open reading frame of the terpene synthase gene from Lilium 'Sorbonne', designated LsTPS, which had 99.55% homology to transcript CL4520.Contig5_All. In addition, 54, 48 and 50 differently expressed transcription factor were identified by pairwise comparisons between the three organs and a regulatory network for monoterpene biosynthesis was constructed.

CONCLUSIONS

Analysis of differentially expressed genes in flower, leaf and bulb scale of lily, using second generation sequencing technology, yielded detailed information on lily metabolic differentiation in three organs. Analysis of the expression of flower scent biosynthesis genes has provided a model for the regulation of the pathway and identified a candidate gene encoding an enzyme catalyzing the final step in scent production. These digital gene expression profiles provide a valuable and informative database for the further identification and analysis of structural genes and transcription factors in different lily organs and elucidation of their function.

Spatiotemporal Transcriptome Analysis Provides Insights into Bicolor Tepal Development in Lilium "Tiny Padhye"

The bicolor Asiatic hybrid lily cultivar "Tiny Padhye" is an attractive variety because of its unique color pattern. During its bicolor tepal development, the upper tepals undergo a rapid color change from green to white, while the tepal bases change from green to purple. However, the molecular mechanisms underlying these changes remain largely uncharacterized. To systematically investigate the dynamics of the lily bicolor tepal transcriptome during development, we generated 15 RNA-seq libraries from the upper tepals (S2-U) and basal tepals (S1-D, S2-D, S3-D, and S4-D) of Lilium "Tiny Padhye." Utilizing the Illumina platform, a total of 295,787 unigenes were obtained from 713.12 million high-quality paired-end reads. A total of 16,182 unigenes were identified as differentially expressed genes during tepal development. Using Kyoto Encyclopedia of Genes and Genomes pathway analysis, candidate genes involved in the anthocyanin biosynthetic pathway (61 unigenes), and chlorophyll metabolic pathway (106 unigenes) were identified. Further analyses showed that most anthocyanin biosynthesis genes were transcribed coordinately in the tepal bases, but not in the upper tepals, suggesting that the bicolor trait of "Tiny Padhye" tepals is caused by the transcriptional regulation of anthocyanin biosynthetic genes. Meanwhile, the high expression level of chlorophyll degradation genes and low expression level of chlorophyll biosynthetic genes resulted in the absence of chlorophylls from "Tiny Padhye" tepals after flowering. Transcription factors putatively involved in the anthocyanin biosynthetic pathway and chlorophyll metabolism in lilies were identified using a weighted gene co-expression network analysis and their possible roles in lily bicolor tepal development were discussed. In conclusion, these extensive transcriptome data provide a platform for elucidating the molecular mechanisms of bicolor tepals in lilies and provide a basis for similar research in other closely related species.

De Novo Transcriptome Analysis of Plant Pathogenic Fungus Myrothecium roridum and Identification of Genes Associated with Trichothecene Mycotoxin Biosynthesis

Myrothecium roridum is a plant pathogenic fungus that infects different crops and decreases the yield of economical crops, including soybean, cotton, corn, pepper, and tomato. Until now, the pathogenic mechanism of M. roridum has remained unclear. Different types of trichothecene mycotoxins were isolated from M. roridum, and trichothecene was considered as a plant pathogenic factor of M. roridum. In this study, the transcriptome of M. roridum in different incubation durations was sequenced using an Illumina Hiseq 2000. A total of 35,485 transcripts and 25,996 unigenes for M. roridum were obtained from 8.0 Gb clean reads. The protein-protein network of the M. roridum transcriptome indicated that the mitogen-activated protein kinases signal pathway also played an important role in the pathogenicity of M. roridum. The genes related to trichothecene biosynthesis were annotated. The expression levels of these genes were also predicted and validated through quantitative real-time polymerase chain reaction. Tri5 gene encoding trichodiene synthase was cloned and expressed, and the purified trichodiene synthase was able to catalyze farnesyl pyrophosphate into different kinds of sesquiterpenoids.Tri4 and Tri11 genes were expressed in Escherichia coli, and their corresponding enzymatic properties were characterized. The phylogenetic tree of trichodiene synthase showed a great discrepancy between the trichodiene synthase from M. roridum and other species. Our study on the genes related to trichothecene biosynthesis establishes a foundation for the M. roridum hazard prevention, thus improving the yields of economical crops.

RNA-seq-based evaluation of bicolor tepal pigmentation in Asiatic hybrid lilies (Lilium spp.)

BACKGROUND

Color patterns in angiosperm flowers are produced by spatially and temporally restricted deposition of pigments. Identifying the mechanisms responsible for restricted pigment deposition is a topic of broad interest. Some dicots species develop bicolor petals, which are often caused by the post-transcriptional gene silencing (PTGS) of chalcone synthase (CHS) genes. An Asiatic hybrid lily (Lilium spp.) cultivar Lollypop develops bicolor tepals with pigmented tips and white bases. Here, we analyzed the global transcription of pigmented and non-pigmented tepal parts from Lollypop, to determine the main transcriptomic differences.

RESULTS

De novo assembly of RNA-seq data yielded 49,239 contigs (39,426 unigenes), which included a variety of novel transcripts, such as those involved in flavonoid-glycosylation and sequestration and in regulation of anthocyanin biosynthesis. Additionally, 1258 of the unigenes exhibited significantly differential expression between the tepal parts (false discovery rates <0.05). The pigmented tepal parts accumulated more anthocyanins, and unigenes annotated as anthocyanin biosynthesis genes (e.g., CHS, dihydroflavonol 4-reductase, and anthocyanidin synthase) were expressed 7-30-fold higher than those in non-pigmented parts. These results indicate that the transcriptional regulation of biosynthesis genes is more likely involved in the development of bicolor lily tepals rather than the PTGS of CHS genes. In addition, the expression level of a unigene homologous to LhMYB12, which often regulates full-tepal anthocyanin pigmentation in lilies, was >2-fold higher in the pigmented parts. Thus, LhMYB12 should be involved in the transcriptional regulation of the biosynthesis genes in bicolor tepals. Other factors that potentially suppress or enhance the expression of anthocyanin biosynthesis genes, including a WD40 gene, were identified, and their involvement in bicolor development is discussed.

CONCLUSIONS

Our results indicate that the bicolor trait of Lollypop tepals is caused by the transcriptional regulation of anthocyanin biosynthesis genes and that the transcription profile of LhMYB12 provides a clue for elucidating the mechanisms of the trait. The tepal transcriptome constructed in this study will accelerate investigations of the genetic controls of anthocyanin color patterns, including the bicolor patterns, of Lilium spp.

Large-scale developing of simple sequence repeat markers and probing its correlation with ramie (Boehmeria nivea L.) fiber quality

Marker-assisted selection is an important component of the discipline of molecular breeding. Using DNA markers to assist in plant breeding, the efficiency and precision could be greatly increased. However, the scarcity number of identified DNA markers has hindered the research and the breeding process of ramie (Boehmeria nivea L.) in many aspects, especially fiber quality, one of the top-priority breeding objectives of ramie. In this study, 4230 SSR loci were identified in 3969 unigenes (6.80 % of 58,369), which were de novo assembled from the transcriptome involving different ramie fiber developmental stages. Among these SSRs, the dinucleotides (1599, 37.80 %) and trinucleotides (772, 18.25 %) were most abundant; the motifs AG/CT (1140, 26.94 %), AT/AT (407, 9.62 %) and AGA/TCT (246, 8.31 %) comprised the three most abundant repeats. A total of 2431 primer pairs were designed flanking the SSRs and 1050 of them were employed in PCR amplification for their usefulness using three ramie cultivars. The results showed that 88.10 % of these primers could generate positive PCR bands in any of the three cultivars. Further phylogenetic analysis that conducted from the PCR amplification of 52 specifically sifted SSR primers within 17 cultivars approved that the possible correlation may exist between the primers and ramie fiber quality. These developed SSR markers could be applied in downstream studies, like genetic and physical maps, quantitative trait loci mapping, genetic diversity studies and cultivar fingerprinting, and breeding processes of ramie with better fiber quality under further confirmation of the correlation with ramie fiber quality.

Gene transcript profiles in the desert plant Nitraria tangutorum during fruit development and ripening

Nitraria tangutorum Bobr., a valuable wild shrub distributed in Northwest China, produces edible and medicinal berries. However, little is known about the molecular mechanisms of its fruit development and ripening. We performed de novo transcriptome sequencing of N. tangutorum fruit using the Illumina HiSeq™ 2000 sequencing platform. More than 62.94 million reads were obtained and assembled into 69,306 unigenes (average length, 587 bp). These unigenes were annotated by querying against five databases (Nr, Swiss-Prot, GO, COG, and KEGG); 42,929 and 26,809 unigenes were found in the Nr and Swiss-Prot databases, respectively. In ortholog analyses, 33,363 unigenes were assigned with one or more GO terms, 15,537 hits were aligned to 25 COG classes, and 24,592 unigenes were classified into 128 KEGG pathways. Digital gene expression analyses were conducted on N. tangutorum fruit at the green (S1), yellow (S2), and red (S3) developmental stages. In total, 8240, 5985, and 4994 differentially expressed genes (DEGs) were detected for S1 vs. S2, S1 vs. S3, and S2 vs. S3, respectively. Cluster analyses showed that a large proportion of DEGs related to plant hormones and transcription factors (TFs) showed high expression in S1, down-regulated expression in S2, and up-regulated expression in S3. We analyzed the expression patterns of 23 genes encoding 12 putative enzymes involved in flavonoid biosynthesis. The expression profiles of 10 DEGs involved in flavonoid biosynthesis were validated by Q-PCR analysis. The assembled and annotated transcriptome sequences and gene expression profile analyses provide valuable genetic resources for research on N. tangutorum.