Transcriptomic Analysis of Flower Bud Differentiation in Magnolia sinostellata

Integrative Metabolomic and Transcriptomic Analysis Elucidates That the Mechanism of Phytohormones Regulates Floral Bud Development in Alfalfa

Floral bud growth influences seed yield and quality; however, the molecular mechanism underlying the development of floral buds in alfalfa (Medicago sativa) is still unclear. Here, we comprehensively analyzed the transcriptome and targeted metabolome across the early, mid, and late bud developmental stages (D1, D2, and D3) in alfalfa. The metabolomic results revealed that gibberellin (GA), auxin (IAA), cytokinin (CK), and jasmonic acid (JA) might play an essential role in the developmental stages of floral bud in alfalfa. Moreover, we identified some key genes associated with GA, IAA, CK, and JA biosynthesis, including CPS, KS, GA20ox, GA3ox, GA2ox, YUCCA6, amid, ALDH, IPT, CYP735A, LOX, AOC, OPR, MFP2, and JMT. Additionally, many candidate genes were detected in the GA, IAA, CK, and JA signaling pathways, including GID1, DELLA, TF, AUX1, AUX/IAA, ARF, GH3, SAUR, AHP, B-ARR, A-ARR, JAR1, JAZ, and MYC2. Furthermore, some TFs related to flower growth were screened in three groups, such as AP2/ERF-ERF, MYB, MADS-M-type, bHLH, NAC, WRKY, HSF, and LFY. The findings of this study revealed the potential mechanism of floral bud differentiation and development in alfalfa and established a theoretical foundation for improving the seed yield of alfalfa.

Integrated transcriptome and proteome analysis provides insights into CpFPA1 for floral induction in Chimonanthus praecox (Magnoliidae) without FLC in genome

KEY MESSAGE

We used transcriptomic and proteomic association analysis to reveal the critical genes/proteins at three key flower bud differentiation stages and overexpression of CpFPA1 in Arabidopsis resulted in earlier flowering. Wintersweet (Chimonanthus praecox), a rare winter-flowering woody plant, is well known for its unique blooming time, fragrance and long flowering period. However, the molecular mechanism of flowering in C. praecox remains poorly unclear. In this study, we used transcriptomic and proteomic association analysis to reveal the critical genes/proteins at three key flower bud (FB) differentiation stages (FB.Apr, FB.May and FB.Nov) in C. praecox. The results showed that a total of 952 differential expressed genes (DEGs) and 40 differential expressed proteins (DEPs) were identified. Gene ontology (GO) enrichment revealed that DEGs in FB.Apr/FB.May comparison group were mainly involved in metabolic of biological process, cell and cell part of cellular component and catalytic activity of molecular function. In the EuKaryotic Orthologous Groups (KOG) functional classification, DEPs were predicted mainly in the function of general function prediction only (KOG0118), post-translational modification, protein turnover and chaperones. The autonomous pathway genes play an essential role in the floral induction. Based on transcriptome and proteome correlation analysis, six candidate genes associated with the autonomous pathway were identified, including FPA1, FPA2a, FPA2b, FCA, FLK, FY. Furthermore, CpFPA1 was isolated and functionally characterized, and ectopic expression of CpFPA1 in Arabidopsis Columbia (Col-0) resulted in earlier flowering. These data could contribute to understand the function of CpFPA1 for floral induction and provide information for further research on the molecular mechanisms of flowering in wintersweet.

Metabolic analysis of the regulatory mechanism of sugars on secondary flowering in Magnolia

Background

Magnolia, a traditional and important ornamental plant in urban greening, has been cultivated for about 2000 years in China for its elegant flower shape and gorgeous flower color. Most varieties of Magnolia bloom once a year in spring, whereas a few others, such as Magnolia liliiflora Desr. ‘Hongyuanbao’, also bloom for the second time in summer or early autumn. Such a twice flowering trait is desirable for its high ornamental value, while its underlying mechanism remains unclear.

Methods

Paraffin section was used to show the flowering time and phenotypic changes of M. liliiflora ‘Hongyuanbao’ during the twice flowering periods from March 28 to August 25, 2018. Gas chromatography-mass spectrometry (GC-MS) was then performed to explore the chemical metabolites through the twice flower bud differentiation process in ‘Hongyuanbao’, and the metabolites were screened and identified by orthogonal projection to latent structures discriminant analysis (OPLS-DA). Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis (KEGG) was used to reveal the relationship between the sugar metabolites and twice-flowering characteristic. To further investigate the potential role of sucrose and trehalose on flowering regulation of ‘Hongyuanbao’, the plants once finished the spring flowering were regularly sprayed with sucrose and trehalose solutions at 30 mM, 60 mM, and 90 mM concentrations from April 22, 2019. The flower bud differentiation processes of sprayed plants were observed and the expression patterns of the genes involved in sucrose and trehalose metabolic pathways were studied by quantitative reverse transcription PCR (qRT-PCR).

Results

It showed that ‘Hongyuanbao’ could complete flower bud differentiation twice in a year and flowered in both spring and summer. The metabolites of flower bud differentiation had a significant variation between the first and second flower buds. Compared to the first flower bud differentiation process, the metabolites in the sucrose and trehalose metabolic pathways were significantly up-regulated during the second flower bud differentiation process. Besides that, the expression levels of a number of trehalose-6-phosphate synthase (TPS) genes including MlTPS1, MlTPS5, MlTPS6, MlTPS7 and MlTPS9 were substantially increased in the second flower differentiation process compared with the first process. Exogenous treatments indicated that compared to the control plants (sprayed with water, CK), all three concentrations of trehalose could accelerate flowering and the effect of 60 mM concentration was the most significant. For the sucrose foliar spray, only the 60 mM concentration accelerated flowering compared with CK. It suggested that different concentration of trehalose and sucrose might have different effects. Expression analysis showed that sucrose treatment increased the transcription levels of MlTPS5 and MlTPS6, whereas trehalose treatment increased MlTPS1, showing that different MlTPS genes took part in sucrose and trehalose metabolic pathways respectively. The expression levels of a number of flowering-related genes, such as MlFT, MlLFY, and MlSPL were also increased in response to the sprays of sucrose and trehalose.

Conclusions

We provide a novel insight into the effect of sucrose and trehalose on the flowering process in Magnolia. Under the different sugar contents treatments, the time of flower bud differentiation of Magnolia was advanced. Induced and accelerated flowering in response to sucrose and trehalose foliar spray, coupled with elevated expression of trehalose regulatory and response genes, suggests that secondary flower bud formation is a promoted by altered endogenous sucrose and trehalose levels. Those results give a new understanding of sucrose and trehalose on twice-flowering in Magnolia and provide a preliminary speculation for inducing and accelerating the flowering process in Magnolia.

Gene identification and tissue expression analysis inform the floral organization and color in the basal angiosperm Magnolia polytepala (Magnoliaceae)

In Magnolia polytepala, the formation of floral organization and color was attributed to tissue-dependent differential expression levels of MADS-box genes and anthocyanin biosynthetic genes. In angiosperms, the diversity of floral morphology and organization suggests its value in exploring plant evolution. Magnolia polytepala, an endemic basal angiosperm species in China, possesses three green sepal-like tepals in the outermost whorl and pink petal-like tepals in the inner three whorls, forming unique floral morphology and organization. However, we know little about its underlying molecular regulatory mechanism. Here, we first reported the full-length transcriptome of M. polytepala using PacBio sequencing. A total of 16 MADS-box transcripts were obtained from the transcriptome data, including floral homeotic genes (e.g., MpAPETALA3) and other non-floral homeotic genes (MpAGL6, etc.). Phylogenetic analysis and spatial expression pattern reflected their putative biological function as their homologues in Arabidopsis. In addition, nine structural genes involved in anthocyanin biosynthesis pathway had been screened out, and tepal color difference was significantly associated with their tissue-dependent differential expression levels. This study provides a relatively comprehensive investigation of the MADS-box family and anthocyanin biosynthetic genes in M. polytepala, and will facilitate our understanding of the regulatory mechanism underlying floral organization and color in basal angiosperms.

Genetic studies on continuous flowering in woody plant Osmanthus fragrans

Continuous flowering is a key horticultural trait in ornamental plants, whereas the specific molecular regulation mechanism remains largely unknown. In sweet osmanthus (Osmanthus fragrans Lour.), plants based on their flowering characteristics are divided into once-flowering (OF) habit and continuous flowering (CF) habit. Here, we first described the flowering phenology shifts of OF and CF habits in sweet osmanthus through paraffin section and microscope assay. Phenotypic characterization showed that CF plants had constant new shoot growth, floral transition, and blooming for 1 year, which might lead to a continuous flowering trait. We performed the transcriptome sequencing of OF and CF sweet osmanthus and analyzed the transcriptional activity of flowering-related genes. Among the genes, three floral integrators, OfFT, OfTFL1, and OfBFT, had a differential expression during the floral transition process in OF and CF habits. The expression patterns of the three genes in 1 year were revealed. The results suggested that their accumulations corresponded to the new shoots occurring and the floral transition process. Function studies suggested that OfFT acted as a flowering activator, whereas OfBFT was a flowering inhibitor. Yeast one-hybrid assay indicated that OfSPL8 was a common upstream transcription factor of OfFT and OfBFT, suggesting the vital role of OfSPL8 in continuous flowering regulation. These results provide a novel insight into the molecular mechanism of continuous flowering.

Systematic Identification and Validation of Suitable Reference Genes for the Normalization of Gene Expression in Prunella vulgaris under Different Organs and Spike Development Stages

The quantitative real-time PCR (qRT-PCR) is an efficient and sensitive method for determining gene expression levels, but the accuracy of the results substantially depends on the stability of the reference gene (RG). Therefore, choosing an appropriate reference gene is a critical step in normalizing qRT-PCR data. Prunella vulgaris L. is a traditional Chinese medicine herb widely used in China. Its main medicinal part is the fruiting spike which is termed Spica Prunellae. However, thus far, few studies have been conducted on the mechanism of Spica Prunellae development. Meanwhile, no reliable RGs have been reported in P. vulgaris. The expression levels of 14 candidate RGs were analyzed in this study in various organs and at different stages of Spica Prunellae development. Four statistical algorithms (Delta Ct, BestKeeper, NormFinder, and geNorm) were utilized to identify the RGs' stability, and an integrated stability rating was generated via the RefFinder website online. The final ranking results revealed that eIF-2 was the most stable RG, whereas VAB2 was the least suitable as an RG. Furthermore, eIF-2 + Histon3.3 was identified as the best RG combination in different periods and the total samples. Finally, the expressions of the PvTAT and Pv4CL2 genes related to the regulation of rosmarinic acid synthesis in different organs were used to verify the stable and unstable RGs. The stable RGs in P. vulgaris were originally identified and verified in this work. This achievement provides strong support for obtaining a reliable qPCR analysis and lays the foundation for in-depth research on the developmental mechanism of Spica Prunellae.

NBLAST: a graphical user interface-based two-way BLAST software with a dot plot viewer

BLAST, a basic bioinformatics tool for searching local sequence similarity, has been one of the most widely used bioinformatics programs since its introduction in 1990. Users generally use the web-based NCBI-BLAST program for BLAST analysis. However, users with large sequence data are often faced with a problem of upload size limitation while using the web-based BLAST program. This proves inconvenient as scientists often want to run BLAST on their own data, such as transcriptome or whole genome sequences. To overcome this issue, we developed NBLAST, a graphical user interface-based BLAST program that employs a two-way system, allowing the use of input sequences either as "query" or "target" in the BLAST analysis. NBLAST is also equipped with a dot plot viewer, thus allowing researchers to create custom database for BLAST and run a dot plot similarity analysis within a single program. It is available to access to the NBLAST with http://nbitglobal.com/nblast.

Transcriptome Analysis Reveals the Role of GA3 in Regulating the Asynchronism of Floral Bud Differentiation and Development in Heterodichogamous Cyclocarya paliurus (Batal.) Iljinskaja

Cyclocarya paliurus is an important medical plant owing to the diverse bioactive compounds in its leaves. However, the heterodichogamy with female and male functions segregation within protandry (PA) or protogyny (PG) may greatly affect seed quality and its plantations for medicinal use. To speculate on the factor playing the dominant role in regulating heterodichogamy in C. paliurus, based on phenotypic observations, our study performed a multi comparison transcriptome analysis on female and male buds (PG and PA types) using RNA-seq. For the female and male bud comparisons, a total of 6753 differentially expressed genes (DEGs) were detected. In addition, functional analysis revealed that these DEGs were significantly enriched in floral development, hormone, and GA-related pathways. As the dominant hormones responsible for floral differentiation and development, gibberellins (GAs) in floral buds from PG and PA types were quantified using HPLC-MS. Among the tested GAs, GA₃ positively regulated the physiological differentiation (S0) and germination (S2) of floral buds. The dynamic changes of GA₃ content and floral morphological features were consistent with the expression levels of GA-related genes. Divergences of GA₃ contents at S0 triggered the asynchronism of physiological differentiation between male and female buds of intramorphs (PA-M vs. PA-F and PG-F vs. PG-M). A significant difference in GA₃ content enlarged this asynchronism at S2. Thus, we speculate that GA₃ plays the dominant role in the formation of heterodichogamy in C. paliurus. Meanwhile, the expression patterns of GA-related DEGs, including CPS, KO, GA20ox, GA2_OX, GID1, and DELLA genes, which play central roles in regulating flower development, coincided with heterodichogamous characteristics. These results support our speculations well, which should be further confirmed.

Physiological Analysis and Transcriptome Sequencing Reveal the Effects of Salt Stress on Banana (Musa acuminata cv. BD) Leaf

The salinization of soil is a widespread environmental problem. Banana (Musa acuminata L.) is a salt-sensitive plant whose growth, development, and production are constrained by salt stresses. However, the tolerance mechanism of this salt-sensitive banana to salt stress is still unclear. This study aimed to investigate the influence of NaCl treatment on phenotypic, physiological, and transcriptome changes in bananas. We found that the content of root activity, MDA, Pro, soluble sugar, soluble protein, and antioxidant enzymes activity in salt-stress treatment were significantly higher than the control in bananas. Transcriptome sequencing result identified an overall of 3,378 differentially expressed genes (DEGs) in banana leaves, and the Kyoto Encyclopedia of Genes and Genomes analysis indicated that these DEGs were involved in phenylpropanoid biosynthesis process, ribosome process, starch and sucrose metabolism, amino sugar process, and plant hormone signal transduction process that had simultaneously changed their expression under salt stress, which indicated these DEGs may play a role in promoting BD banana growth under salt treatments. The genes which were enriched in the phenylpropanoid biosynthesis process, starch and sucrose metabolism process, amino sugar process, and plant hormone signal transduction process were specifically regulated to respond to the salt stress treatments. Here, totally 48 differentially expressed transcription factors (TFs), including WRKY, MYB, NAC, and bHLH, were annotated in BD banana under salt stress. In the phenylpropane biosynthesis pathway, all transcripts encoding key enzymes were found to be significantly up-regulated, indicating that the genes in these pathways may play a significant function in the response of BD banana to salt stress. In conclusion, this study provides new insights into the mechanism of banana tolerance to salt stress, which provides a potential application for the genetic improvement of banana with salt tolerance.

QTL and candidate gene identification of the node of the first fruiting branch (NFFB) by QTL-seq in upland cotton (Gossypium hirsutum L.)

Background

The node of the first fruiting branch (NFFB) is an important precocious trait in cotton. Many studies have been conducted on the localization of quantitative trait loci (QTLs) and genes related to fiber quality and yield, but there has been little attention to traits related to early maturity, especially the NFFB, in cotton.

Results

To identify the QTL associated with the NFFB in cotton, a BC₄F₂ population comprising 278 individual plants was constructed. The parents and two DNA bulks for high and low NFFB were whole genome sequenced, and 243.8 Gb of clean nucleotide data were generated. A total of 449,302 polymorphic SNPs and 135,353 Indels between two bulks were identified for QTL-seq. Seventeen QTLs were detected and localized on 11 chromosomes in the cotton genome, among which two QTLs (qNFFB-Dt2–1 and qNFFB-Dt3–3) were located in hotspots. Two candidate genes (GhAPL and GhHDA5) related to the NFFB were identified using quantitative real-time PCR (qRT-PCR) and virus-induced gene silencing (VIGS) experiments in this study. Both genes exhibited higher expression levels in the early-maturing cotton material RIL182 during flower bud differentiation, and the silencing of GhAPL and GhHDA5 delayed the flowering time and increased the NFFB compared to those of VA plants in cotton.

Conclusions

Our study preliminarily found that GhAPL and GhHDA5 are related to the early maturity in cotton. The findings provide a basis for the further functional verification of candidate genes related to the NFFB and contribute to the study of early maturity in cotton.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08164-2.

Genome-Wide Identification MIKC-Type MADS-Box Gene Family and Their Roles during Development of Floral Buds in Wheel Wingnut (Cyclocarya paliurus)

MADS-box transcription factors (TFs) have fundamental roles in regulating floral organ formation and flowering time in flowering plants. In order to understand the function of MIKC-type MADS-box family genes in Cyclocarya paliurus (Batal.) Iljinskaja, we first implemented a genome-wide analysis of MIKC-type MADS-box genes in C. paliurus. Here, the phylogenetic relationships, chromosome location, conserved motif, gene structure, promoter region, and gene expression profile were analyzed. The results showed that 45 MIKC-type MADS-box were divided into 14 subfamilies: BS (3), AGL12 (1), AP3-PI (3), MIKC* (3), AGL15 (3), SVP (5), AGL17 (2), AG (3), TM8 (1), AGL6 (2), SEP (5), AP1-FUL (6), SOC1 (7), and FLC (1). The 43 MIKC-type MADS-box genes were distributed unevenly in 14 chromosomes, but two members were mapped on unanchored scaffolds. Gene structures were varied in the same gene family or subfamily, but conserved motifs shared similar distributions and sequences. The element analysis in promoters’ regions revealed that MIKC-type MADS-box family genes were associated with light, phytohormone, and temperature responsiveness, which may play important roles in floral development and differentiation. The expression profile showed that most MIKC-type MADS-box genes were differentially expressed in six tissues (specifically expressed in floral buds), and the expression patterns were also visibly varied in the same subfamily. CpaF1st24796 and CpaF1st23405, belonging to AP3-PI and SEP subfamilies, exhibited the high expression levels in PA-M and PG-F, respectively, indicating their functions in presenting heterodichogamy. We further verified the MIKC-type MADS-box gene expression levels on the basis of transcriptome and qRT-PCR analysis. This study would provide a theoretical basis for classification, cloning, and regulation of flowering mechanism of MIKC-type MADS-box genes in C. paliurus.

Genome-wide identification of MIKC-type genes related to stamen and gynoecium development in Liriodendron

The organogenesis and development of reproductive organs, i.e., stamen and gynoecium, are important floral characteristics that are closely related to pollinators and reproductive fitness. As a genus from Magnoliaceae, Liriodendron has only two relict species: L. chinense and L. tulipifera. Despite the similar flower shapes of these species, their natural seed-setting rates differ significantly, implying interspecies difference in floral organogenesis and development. MADS-box genes, which participate in floral organogenesis and development, remain unexplored in Liriodendron. Here, to explore the interspecies difference in floral organogenesis and development and identify MADS-box genes in Liriodendron, we examined the stamen and gynoecium primordia of the two Liriodendron species by scanning electron microscopy combined with paraffin sectioning, and then collected two types of primordia for RNA-seq. A total of 12 libraries were constructed and 42,268 genes were identified, including 35,269 reference genes and 6,999 new genes. Monoterpenoid biosynthesis was enriched in L. tulipifera. Genome-wide analysis of 32 MADS-box genes was conducted, including phylogenetic trees, exon/intron structures, and conserved motif distributions. Twenty-six genes were anchored on 17 scaffolds, and six new genes had no location information. The expression profiles of MIKC-type genes via RT-qPCR acrossing six stamen and gynoecium developmental stages indicates that the PI-like, AG/STK-like, SEP-like, and SVP-like genes may contribute to the species-specific differentiation of the organogenesis and development of reproductive organs in Liriodendron. Our findings laid the groundwork for the future exploration of the mechanism underlying on the interspecific differences in reproductive organ development and fitness in Liriodendron.

High-resolution temporal dynamic transcriptome landscape reveals a GhCAL-mediated flowering regulatory pathway in cotton (Gossypium hirsutum L.)

The transition from vegetative to reproductive growth is very important for early maturity in cotton. However, the genetic control of this highly dynamic and complex developmental process remains unclear. A high-resolution tissue- and stage-specific transcriptome profile was generated from six developmental stages using 72 samples of two early-maturing and two late-maturing cotton varieties. The results of histological analysis of paraffin sections showed that flower bud differentiation occurred at the third true leaf stage (3TLS) in early-maturing varieties, but at the fifth true leaf stage (5TLS) in late-maturing varieties. Using pairwise comparison and weighted gene co-expression network analysis, 5312 differentially expressed genes were obtained, which were divided into 10 gene co-expression modules. In the MElightcyan module, 46 candidate genes regulating cotton flower bud differentiation were identified and expressed at the flower bud differentiation stage. A novel key regulatory gene related to flower bud differentiation, GhCAL, was identified in the MElightcyan module. Anti-GhCAL transgenic cotton plants exhibited late flower bud differentiation and flowering time. GhCAL formed heterodimers with GhAP1-A04/GhAGL6-D09 and regulated the expression of GhAP1-A04 and GhAGL6-D09. GhAP1-A04- and GhAGL6-D09-silenced plants also showed significant late flowering. Finally, we propose a new flowering regulatory pathway mediated by GhCAL. This study elucidated the molecular mechanism of cotton flowering regulation and provides good genetic resources for cotton early-maturing breeding.

Genome-wide identification and expression patterns analysis of the RPD3/HDA1 gene family in cotton

BACKGROUND

Histone deacetylases (HDACs) catalyze histone deacetylation and suppress gene transcription during various cellular processes. Within the superfamily of HDACs, RPD3/HDA1-type HDACs are the most studied, and it is reported that RPD3 genes play crucial roles in plant growth and physiological processes. However, there is a lack of systematic research on the RPD3/HDA1 gene family in cotton.

RESULTS

In this study, genome-wide analysis identified 9, 9, 18, and 18 RPD3 genes in Gossypium raimondii, G. arboreum, G. hirsutum, and G. barbadense, respectively. This gene family was divided into 4 subfamilies through phylogenetic analysis. The exon-intron structure and conserved motif analysis revealed high conservation in each branch of the cotton RPD3 genes. Collinearity analysis indicated that segmental duplication was the primary driving force during the expansion of the RPD3 gene family in cotton. There was at least one presumed cis-element related to plant hormones in the promoter regions of all GhRPD3 genes, especially MeJA- and ABA-responsive elements, which have more members than other hormone-relevant elements. The expression patterns showed that most GhRPD3 genes had relatively high expression levels in floral organs and performed higher expression in early-maturity cotton compared with late-maturity cotton during flower bud differentiation. In addition, the expression of GhRPD3 genes could be significantly induced by one or more abiotic stresses as well as exogenous application of MeJA or ABA.

CONCLUSIONS

Our findings reveal that GhRPD3 genes may be involved in flower bud differentiation and resistance to abiotic stresses, which provides a basis for further functional verification of GhRPD3 genes in cotton development and a foundation for breeding better early-maturity cotton cultivars in the future.

A New Insight into Flowering Regulation: Molecular Basis of Flowering Initiation in Magnolia × soulangeana 'Changchun'

Magnolia × soulangeana ‘Changchun’ are trees that bloom in spring and summer respectively after flower bud differentiation. Here, we use phenological and morphological observation and RNA-seq technology to study the molecular basis of flowering initiation in ‘Changchun’. During the process of flowering initiation in spring and summer, the growth of expanded flower buds increased significantly, and their shape was obviously enlarged, which indicated that flowering was initiated. A total of 168,120 expressed genes were identified in spring and summer dormant and expanded flower buds, of which 11,687 genes showed significantly differential expression between spring and summer dormant and expanded flower buds. These differentially expressed genes (DEGs) were mainly involved in plant hormone signal transduction, metabolic processes, cellular components, binding, and catalytic activity. Analysis of differential gene expression patterns revealed that gibberellin signaling, and some transcription factors were closely involved in the regulation of spring and summer flowering initiation in ‘Changchun’. A qRT-PCR (quantitative Real Time Polymerase Chain Reaction) analysis showed that BGISEQ-500 sequencing platform could truly reflect gene expression patterns. It also verified that GID1B (GIBBERELLIN INSENSITIVE DWARF1 B), GID1C, SPL8 (SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 8), and GASA (GIBBERELLIC ACID-STIMULATED ARABIDOPSIS) family genes were expressed at high levels, while the expression of SPY (SPINDLY) was low during spring and summer flowering initiation. Meanwhile, the up- and down-regulated expression of, respectively, AGL6 (AGAMOUS-LIKE 6) and DREB3 (DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 3), AG15, and CDF1 (CYCLIC DOF FACTOR 1) might also be involved in the specific regulation of spring and summer flowering initiation. Obviously, flowering initiation is an important stage of the flowering process in woody plants, involving the specific regulation of relevant genes and transcription factors. This study provides a new perspective for the regulation of the flowering process in perennial woody plants.

Study on cyanidin metabolism in petals of pink-flowered strawberry based on transcriptome sequencing and metabolite analysis

BACKGROUND

Pink-flowered strawberry is a promising new ornamental flower derived from intergeneric hybridization (Fragaria × Potentilla) with bright color, a prolonged flowering period and edible fruits. Its flower color ranges from light pink to red. Pigment compounds accumulated in its fruits were the same as in cultivated strawberry fruits, but different from that in its flowers. However, the transcriptional events underlying the anthocyanin biosynthetic pathway have not been fully characterized in petal coloration. To gain insights into the regulatory networks related to anthocyanin biosynthesis and identify the key genes, we performed an integrated analysis of the transcriptome and metabolome in petals of pink-flowered strawberry.

RESULTS

The main pigments of red and dark pink petals were anthocyanins, among which cyanidins were the main compound. There were no anthocyanins detected in the white-flowered hybrids. A total of 50,285 non-redundant unigenes were obtained from the transcriptome databases involved in red petals of pink-flowered strawberry cultivar Sijihong at three development stages. Amongst the unigenes found to show significant differential expression, 57 were associated with anthocyanin or other flavonoid biosynthesis, in which they were regulated by 241 differentially expressed members of transcription factor families, such as 40 MYBs, 47 bHLHs, and 41 NACs. Based on a comprehensive analysis relating pigment compounds to gene expression profiles, the mechanism of flower coloration was examined in pink-flowered strawberry. A new hypothesis was proposed to explain the lack of color phenotype of the white-flowered strawberry hybrids based on the transcriptome analysis. The expression patterns of FpDFR and FpANS genes corresponded to the accumulation patterns of cyanidin contents in pink-flowered strawberry hybrids with different shades of pink. Moreover, FpANS, FpBZ1 and FpUGT75C1 genes were the major factors that led to the absence of anthocyanins in the white petals of pink-flowered strawberry hybrids. Meanwhile, the competitive effect of FpFLS and FpDFR genes might further inhibit anthocyanin synthesis.

CONCLUSIONS

The data presented herein are important for understanding the molecular mechanisms underlying the petal pigmentation and will be powerful for integrating novel potential target genes to breed valuable pink-flowered strawberry cultivars.

Physiological Analysis and Transcriptome Profiling of Inverted Cuttings of Populus yunnanensis Reveal That Cell Wall Metabolism Plays a Crucial Role in Responding to Inversion

Inverted cuttings of Populus yunnanensis remain alive by rooting from the original morphological apex and sprouting from the base, but the lateral branches exhibit less vigorous growth than those of the upright plant. In this study, we examined the changes in hormone contents, oxidase activities, and transcriptome profiles between upright and inverted cuttings of P. yunnanensis. The results showed that the indole-3-acetic acid (IAA) and gibberellic acid (GA₃) contents were significantly lower in inverted cuttings than in upright cuttings only in the late growth period (September and October), while the abscisic acid (ABA) level was always similar between the two direction types. The biosynthesis of these hormones was surprisingly unrelated to the inversion of P. yunnanensis during the vegetative growth stage (July and August). Increased levels of peroxidases (PODs) encoded by 13 differentially expressed genes (DEGs) served as lignification promoters that protected plants against oxidative stress. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis showed that most DEGs (107) were related to carbohydrate metabolism. Furthermore, altered activities of uridine diphosphate (UDP)-sugar pyrophosphorylase (USP, 15 DEGs) for nucleotide sugars, pectin methylesterase (PME, 7 DEGs) for pectin, and POD (13 DEGs) for lignin were important factors in the response of the trees to inversion, and these enzymes are all involved cell wall metabolism.