Genome-wide transcriptome profiling of Carica papaya L. embryogenic callus

Integration analysis of transcriptome and proteome profiles brings new insights of somatic embryogenesis of two eucalyptus species

BACKGROUND

Somatic embryogenesis (SE) is recognized as a promising technology for plant vegetative propagation. Although previous studies have identified some key regulators involved in the SE process in plant, our knowledge about the molecular changes in the SE process and key regulators associated with high embryogenic potential is still poor, especially in the important fiber and energy source tree - eucalyptus.

RESULTS

In this study, we analyzed the transcriptome and proteome profiles of E. camaldulensis (with high embryogenic potential) and E. grandis x urophylla (with low embryogenic potential) in SE process: callus induction and development. A total of 12,121 differentially expressed genes (DEGs) and 3,922 differentially expressed proteins (DEPs) were identified in the SE of the two eucalyptus species. Integration analysis identified 1,353 (131 to 546) DEGs/DEPs shared by the two eucalyptus species in the SE process, including 142, 13 and 186 DEGs/DEPs commonly upregulated in the callus induction, maturation and development, respectively. Further, we found that the trihelix transcription factor ASR3 isoform X2 was commonly upregulated in the callus induction of the two eucalyptus species. The SOX30 and WRKY40 TFs were specifically upregulated in the callus induction of E. camaldulensis. Three TFs (bHLH62, bHLH35 isoform X2, RAP2-1) were specifically downregulated in the callus induction of E. grandis x urophylla. WGCNA identified 125 and 26 genes/proteins with high correlation (Pearson correlation > 0.8 or < -0.8) with ASR3 TF in the SE of E. camaldulensis and E. grandis x urophylla, respectively. The potential target gene expression patterns of ASR3 TF were then validated using qRT-PCR in the material.

CONCLUSIONS

This is the first time to integrate multiple omics technologies to study the SE of eucalyptus. The findings will enhance our understanding of molecular regulation mechanisms of SE in eucalyptus. The output will also benefit the eucalyptus breeding program.

Editing of SlWRKY29 by CRISPR-activation promotes somatic embryogenesis in Solanum lycopersicum cv. Micro-Tom

At present, the development of plants with improved traits like superior quality, high yield, or stress resistance, are highly desirable in agriculture. Accelerated crop improvement, however, must capitalize on revolutionary new plant breeding technologies, like genetically modified and gene-edited crops, to heighten food crop traits. Genome editing still faces ineffective methods for the transformation and regeneration of different plant species and must surpass the genotype dependency of the transformation process. Tomato is considered an alternative plant model system to rice and Arabidopsis, and a model organism for fleshy-fruited plants. Furthermore, tomato cultivars like Micro-Tom are excellent models for tomato research due to its short life cycle, small size, and capacity to grow at high density. Therefore, we developed an indirect somatic embryo protocol from cotyledonary tomato explants and used this to generate epigenetically edited tomato plants for the SlWRKY29 gene via CRISPR-activation (CRISPRa). We found that epigenetic reprogramming for SlWRKY29 establishes a transcriptionally permissive chromatin state, as determined by an enrichment of the H3K4me3 mark. A whole transcriptome analysis of CRISPRa-edited pro-embryogenic masses and mature somatic embryos allowed us to characterize the mechanism driving somatic embryo induction in the edited tomato cv. Micro-Tom. Furthermore, we show that enhanced embryo induction and maturation are influenced by the transcriptional effector employed during CRISPRa, as well as by the medium composition and in vitro environmental conditions such as osmotic components, plant growth regulators, and light intensity.

Identification and functional analysis of LpNAC37 associated with somatic embryogenesis in Lilium pumilum DC. Fisch. based on transcriptome analysis

Somatic embryogenesis (SE) is important for Lilium bulb propagation, germplasm conservation, and genetic transformation. The transition of somatic cells to embryonic cells is a critical step in SE, but the associated regulatory mechanisms have not been fully elucidated. Lilium pumilum DC. Fisch has a high regenerative capacity, and this study clarifies the critical timing of embryonic cell appearance in Lilium SE. Transcriptome sequencing using RNA-seq technology was performed on 5 representative samples from the early stage of Lilium SE. The 15 established cDNA libraries yielded 91.47 GB of valid data, and a total of 11,155 genes were consistently differentially expressed in the early stages of Lilium SE. GO annotation and KEGG pathway analysis of differentially expressed genes (DEGs) suggested that transcriptional regulation, hormone signaling, and stress response pathways play essential roles in the early stages of Lilium SE. WOX8, WOX11, SHR2, NAC37, AHP2, ANT, PIN1C, LAX2, LBD4, ACS12, YUC4, NFYB3, WRKY28, SAUR50, PYL9, and WRKY39 may be candidate genes for regulating early SE in Lilium. We further cloned LpNAC37, one of the key DEGs obtained from WGCNA and screening. LpNAC37 encodes a protein of 303 amino acids with a conserved NAM structural domain. The protein is a nuclear transcription factor with the highest homology to carrot DcNAC37. Overexpression of LpNAC37 suggested that LpNAC37 promotes embryonic callus formation in Arabidopsis. These results will help reveal the molecular mechanisms of the early stages of Lilium SE and advance the application of SE in Lilium propagation and genetic transformation.

Comparative transcriptome analysis of high- and low-embryogenic Hevea brasiliensis genotypes reveals involvement of phytohormones in somatic embryogenesis

BACKGROUND

Rubber plant (Hevea brasiliensis) is one of the major sources of latex. Somatic embryogenesis (SE) is a promising alterative to its propagation by grafting and seed. Phytohormones have been shown to influence SE in different plant species. However, limited knowledge is available on the role of phytohormones in SE in Hevea. The anther cultures of two Hevea genotypes (Yunyan 73477-YT and Reken 628-RT) with contrasting SE rate were established and four stages i.e., anthers (h), anther induced callus (y), callus differentiation state (f), and somatic embryos (p) were studied. UPLC-ESI-MS/MS and transcriptome analyses were used to study phytohormone accumulation and related expression changes in biosynthesis and signaling genes.

RESULTS

YT showed higher callus induction rate than RT. Of the two genotypes, only YT exhibited successful SE. Auxins, cytokinins (CKs), abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), gibberellins (GAs), and ethylene (ETH) were detected in the two genotypes. Indole-3-acetic acid (IAA), CKs, ABA, and ETH had notable differences in the studied stages of the two genotypes. The differentially expressed genes identified in treatment comparisons were majorly enriched in MAPK and phytohormone signaling, biosynthesis of secondary metabolites, and metabolic pathways. The expression changes in IAA, CK, ABA, and ETH biosynthesis and signaling genes confirmed the differential accumulation of respective phytohormones in the two genotypes.

CONCLUSION

These results suggest potential roles of phytohormones in SE in Hevea.

Integrated proteome and acetylome analyses provide novel insights into early somatic embryogenesis of Dimocarpus longan

Longan (Dimocarpus longan) is a precious subtropical fruit with high nutritional value. The somatic embryogenesis (SE) affects the quality and yield of fruit. Apart from clonal propagation, SE has extensive applications in genetic improvement and mutation. Thus, understanding the molecular basis of embryogenesis in longan will help to develop strategies for mass production of quality planting material. Lysine acetylation (Kac) plays an important role in diverse cellular processes, but limited knowledge is available regarding acetylation modifications in plant early SE. In this study, the proteome and acetylome of longan embryogenic callus (ECs) and globular embryos (GEs) were investigated. In total, 7232 proteins and 14,597 Kac sites were identified, and this resulted in the discovery of 1178 differentially expressed proteins and 669 differentially expressed acetylated proteins. KEGG and GO analysis showed that glucose metabolism, carbon metabolism, fatty acid degradation, and oxidative phosphorylation pathways were influenced by Kac modification. Furthermore, sodium butyrate (Sb, a deacetylase inhibitor) led to reduced the proliferation and delayed the differentiation of ECs by regulating the homeostasis of reactive oxygen species (ROS) andindole-3-acetic acid (IAA). Our study provides a comprehensive proteomic and acetylomic analysis to aid in understanding the molecular mechanisms involved in early SE, representing a potential tool for genetic improvement of longan.

Proteome profiles during early stage of somatic embryogenesis of two Eucalyptus species

BACKGROUND

Somatic embryogenesis (SE) was recognized as an important tool for plants to propagate. However, our knowledge about the proteins involved in early SE including the callus dedifferentiation is still limited, especially in the economic woody tree - Eucalyptus.

RESULTS

We used the data-independent acquisition mass-spectrometry to study the different proteome profiles of early SE of two Eucalyptus species-E. camaldulensis (high regeneratively potential) and E. grandis x urophylla (low regenerative potential). Initially, 35,207 peptides and 7,077 proteins were identified in the stem and tissue-culture induced callus of the two Eucalyptus species. MSstat identified 2,078 and 2,807 differentially expressed proteins (DEPs) in early SE of E. camaldulensis and E. grandis x urophylla, respectively. They shared 760 upregulated and 420 downregulated proteins, including 4 transcription factors, 31 ribosomal proteins, 1 histone, 3 zinc finger proteins (ZFPs), 16 glutathione transferases, 10 glucosyltransferases, ARF19, WOX8 and PIN1. These proteins might be involved in the early SE of Eucalyptus. By combining the miRNA and RNA-Seq results, some miRNA ~ gene/protein regulatory networks were identified in early SE of Eucalyptus, such as miR160 ~ TPP2, miR164 ~ UXS2, miR169 ~ COX11 and miR535 ~ Eucgr.E01067. Further, we found SERK, WRKY, ZFP and ABC transporter might be related with high SE potential.

CONCLUSIONS

Overall, our study identified proteins involved in the early SE and related to the high regeneration potential of Eucalyptus. It greatly enhanced our understanding of the early SE and the SE capacity of Eucalyptus.

Establishment of in vitro regeneration system and molecular analysis of early development of somatic callus in Capsicum chinense and Capsicum baccatum

Regeneration is extremely important to pepper genetic development; however, the molecular mechanisms of how the callus reactivates cell proliferation and promotes cell reprogramming remain elusive in pepper. In the present study, C. baccatum (HNUCB81 and HNUCB226) and C. chinense (HNUCC22 and HNUCC16) were analyzed to reveal callus initiation by in vitro regeneration, histology, and transcriptome. We successfully established an efficient in vitro regeneration system of two cultivars to monitor the callus induction of differential genotypes, and the regenerated plants were obtained. Compared to C. chinense, there was a higher callus induction rate in C. baccatum. The phenotype of C. baccatum changed significantly and formed vascular tissue faster than C. chinense. The KEGG enrichment analysis found that plant hormone transduction and starch and sucrose metabolism pathways were significantly enriched. In addition, we identified that the WOX7 gene was significantly up-regulated in HNUCB81 and HNUCB226 than that in HNUCC22 and HNUCC16, which may be a potential function in callus formation. These results provided a promising strategy to improve the regeneration and transformation of pepper plants.

Transcriptomic and Metabolomic Analysis of Korean Pine Cell Lines with Different Somatic Embryogenic Potential

The embryogenesis capacity of conifer callus is not only highly genotype-dependent, but also gradually lost after long-term proliferation. These problems have seriously limited the commercialization of conifer somatic embryogenesis (SE) technology. In this study, the responsive SE cell line (R-EC), the blocked SE cell line (B-EC), and the loss of SE cell line (L-EC) were studied. The morphological, physiological, transcriptomic, and metabolomic profiles of these three types of cells were analyzed. We found that R-EC had higher water content, total sugar content, and putrescine (Put) content, as well as lower superoxide dismutase (SOD) activity and H2O2 content compared to B-EC and L-EC. A total of 2566, 13,768, and 13,900 differentially expressed genes (DEGs) and 219, 253, and 341 differentially expressed metabolites (DEMs) were found in the comparisons of R-EC versus B-EC, R-EC versus B-EC, and B-EC versus L-EC, respectively. These DEGs and DEMs were mainly found to be involved in plant signal transduction, starch and sugar metabolism, phenylpropane metabolism, and flavonoid metabolism. We found that the AUX1 and AUX/IAA families of genes were significantly up-regulated after the long-term proliferation of callus, resulting in higher auxin content. Most phenylpropane and flavonoid metabolites, which act as antioxidants to protect cells from damage, were found to be significantly up-regulated in R-EC.

Mitochondrial proteomics reveals new insights into embryogenic competence acquisition in Carica papaya L. callus

Understanding the mechanisms that endow a somatic cell with the ability to differentiate into a somatic embryo, which could result in numerous biotechnological applications, is still a challenge. The objective of this work was to identify some of the molecular and physiological mechanisms responsible for the acquisition of embryogenic competence during somatic embryogenesis in Carica papaya L. We performed a broad characterization of embryogenic (EC) and nonembryogenic calli (NEC) of using global and mitochondrial proteomic approaches, histomorphology, histochemistry, respiratory activity, and endogenous hormonal and hydrogen peroxide (H₂O₂) contents. EC and NEC presented remarkable differences in anatomical and histochemical characteristics, with EC showing a higher reactivity for the presence of proteins and neutral polysaccharides. Our results demonstrate that mitochondrial metabolism affects the embryogenic competence of C. papaya callus. The EC presented higher participation of alternative oxidase (AOX) enzymes, higher total cell respiration and presented a stronger accumulation of mitochondrial stress response proteins. Differential accumulation of auxin-responsive Gretchen Hagen 3 (GH3) family proteins in EC was related to a decrease in the content of free 2,4-dichlorophenoxyacetic acid (2,4-D). EC also showed higher endogenous H₂O₂ contents. H₂O₂ is a promising molecule for further investigation in differentiation protocols for C. papaya somatic embryos. SIGNIFICANCE: To further advance the understanding of somatic embryogenesis, we performed a broad characterization of embryogenic and nonembryogenic callus, through global and mitochondrial proteomic approaches, histomorphology, histochemistry, respiratory activity, and endogenous hormonal and hydrogen peroxide contents. Based on these results, we propose a working model for the competence of papaya callus. This model suggests that GH3 proteins play an important role in the regulation of auxins. In addition, embryogenic callus showed a greater abundance of stress response proteins and folding proteins. Embryogenic callus respiration occurs predominantly via AOX, and the inhibition of its activity is capable of inhibiting callus differentiation. Although the embryogenic callus presented greater total respiration and a greater abundance of oxidative phosphorylation proteins, they had less COX participation and less coupling efficiency, indicating less ATP production.

Global Transcriptome and Coexpression Network Analyses Reveal New Insights Into Somatic Embryogenesis in Hybrid Sweetgum (Liquidambar styraciflua × Liquidambar formosana)

Somatic embryogenesis (SE) is a process of somatic cells that dedifferentiate to totipotent embryonic stem cells and generate embryos in vitro. Despite recent scientific headway in deciphering the difficulties of somatic embryogenesis, the overall picture of key genes, pathways, and co-expression networks regulating SE is still fragmented. Therefore, deciphering the molecular basis of somatic embryogenesis of hybrid sweetgum remains pertinent. In the present study, we analyzed the transcriptome profiles and gene expression regulation changes via RNA sequencing from three distinct developmental stages of hybrid sweetgum: non-embryogenic callus (NEC), embryogenic callus (EC), and redifferentiation. Comparative transcriptome analysis showed that 19,957 genes were differentially expressed in ten pairwise comparisons of SE. Among these, plant hormone signaling-related genes, especially the auxin and cytokinin signaling components, were significantly enriched in NEC and EC early. The K-means method was used to identify multiple transcription factors, including HB-WOX, B3-ARF, AP2/ERF, and GRFs (growth regulating factors). These transcription factors showed distinct stage- or tissue-specific expression patterns mirroring each of the 12 superclusters to which they belonged. For example, the WOX transcription factor family was expressed only at NEC and EC stages, ARF transcription factor was expressed in EC early, and GRFs was expressed in late SE. It was noteworthy that the AP2/ERF transcription factor family was expressed during the whole SE process, but almost not in roots, stems and leaves. A weighted gene co-expression network analysis (WGCNA) was used in conjunction with the gene expression profiles to recognize the genes and modules that may associate with specific tissues and stages. We constructed co-expression networks and revealed 22 gene modules. Four of these modules with properties relating to embryonic potential, early somatic embryogenesis, and somatic embryo development, as well as some hub genes, were identified for further functional studied. Through a combination analysis of WGCNA and K-means, SE-related genes including AUX22, ABI3, ARF3, ARF5, AIL1, AIL5, AGL15, WOX11, WOX9, IAA29, BBM1, MYB36, LEA6, SMR4 and others were obtained, indicating that these genes play an important role in the processes underlying the progression from EC to somatic embryos (SEs) morphogenesis. The transcriptome information provided here will form the foundation for future research on genetic transformation and epigenetic control of plant embryogenesis at a molecular level. In follow-up studies, these data could be used to construct a regulatory network for SE; Key genes obtained from coexpression network analysis at each critical stage of somatic embryo can be considered as potential candidate genes to verify these networks.

Auxin and cytokinin mediated regulation involved in vitro organogenesis of papaya

In vitro organogenesis is a multistep process which is largely controlled by the balance between auxin and cytokinin. Previous studies revealed a complex network regulating in vitro organogenesis in Arabidopsis thaliana; however, our knowledge of the molecular mechanisms underlying de novo shoot formation in papaya (Carica papaya) remains limited. Here, we optimized multiple factors to achieve an efficient and reproducible protocol for the induction of papaya callus formation and shoot regeneration. Subsequently, we analyzed the dynamic transcriptome profiles of samples undergoing this process, identified 5381, 642, 4047, and 2386 differentially expressed genes (DEGs), including 447, 66, 350, and 263 encoding transcription factors (TFs), in four stage comparisons. The DEGs were mainly involved in phytohormone modulation and transduction processes, particularly for auxin and cytokinin. Of these, 21 and 7 candidate genes involved in the auxin and cytokinin pathways, respectively, had distinct expression patterns throughout in vitro organogenesis. Furthermore, we found two genes encoding key TFs, CpLBD19 and CpESR1, were sharply induced on callus induction medium and shoot induction medium, indicating these two TFs may serve as proxies for callus induction and shoot formation in papaya. We therefore report a regulatory network of auxin and cytokinin signaling in papaya according to the one previously modeled for Arabidopsis. Our comprehensive analyses provide insight into the early molecular regulation of callus initiation and shoot formation in papaya, and are useful for the further identification of the regulators governing in vitro organogenesis.

Transcriptomes analysis reveals novel insight into the molecular mechanisms of somatic embryogenesis in Hevea brasiliensis

BACKGROUND

Somatic embryogenesis (SE) is a promising technology for plant vegetative propagation, which has an important role in tree breeding. Though rubber tree (Hevea brasiliensis Muell. Arg.) SE has been founded, few late SE-related genes have been identified and the molecular regulation mechanisms of late SE are still not well understood.

RESULTS

In this study, the transcriptomes of embryogenic callus (EC), primary embryo (PE), cotyledonary embryo (CE), abnormal embryo (AE), mature cotyledonary embryo (MCE) and withered abnormal embryo (WAE) were analyzed. A total of 887,852,416 clean reads were generated, 85.92% of them were mapped to the rubber tree genome. The de novo assembly generated 36,937 unigenes. The differentially expressed genes (DEGs) were identified in the pairwise comparisons of CE vs. AE and MCE vs. WAE, respectively. The specific common DEGs were mainly involved in the phytohormones signaling pathway, biosynthesis of phenylpropanoid and starch and sucrose metabolism. Among them, hormone signal transduction related genes were significantly enriched, especially the auxin signaling factors (AUX-like1, GH3.1, SAUR32-like, IAA9-like, IAA14-like, IAA27-like, IAA28-like and ARF5-like). The transcription factors including WRKY40, WRKY70, MYBS3-like, MYB1R1-like, AIL6 and bHLH93-like were characterized as molecular markers for rubber tree late SE. CML13, CML36, CAM-7, SERK1 and LEAD-29-like were also related to rubber tree late SE. In addition, histone modification had crucial roles during rubber tree late SE.

CONCLUSIONS

This study provides important information to elucidate the molecular regulation during rubber tree late SE.

Discovery of SNPs and InDels in papaya genotypes and its potential for marker assisted selection of fruit quality traits

Papaya is a tropical and climacteric fruit that is recognized for its nutritional benefits and medicinal applications. Its fruits ripen quickly and show a drastic fruit softening, leading to great post-harvest losses. To overcome this scenario, breeding programs of papaya must invest in exploring the available genetic variation to continue developing superior cultivars with improved fruit quality traits. The objective of this study was to perform a whole-genome genotyping (WGG) of papaya, predict the effects of the identified variants, and develop a list of ripening-related genes (RRGs) with linked variants. The Formosa elite lines of papaya Sekati and JS-12 were submitted to WGG with an Illumina Miseq platform. The effects of variants were predicted using the snpEff program. A total of 28,451 SNPs having Ts/Tv (Transition/Transversion) ratio of 2.45 and 1,982 small insertions/deletions (InDels) were identified. Most variant effects were predicted in non-coding regions, with only 2,104 and 138 effects placed in exons and splice site regions, respectively. A total of 106 RRGs were found to be associated with 460 variants, which may be converted into PCR markers to facilitate genetic mapping and diversity studies and to apply marker-assisted selection (MAS) for specific traits in papaya breeding programs.

Functional characterization of a WRKY family gene involved in somatic embryogenesis in Panax ginseng

As a perennial herbaceous species, Panax ginseng is widely cultivated and used as traditional herbal medicine. The root of Panax ginseng commonly remains expensive as conventional breeding of Panax ginseng is difficult. Somatic embryogenesis (S.E.) is a useful tool for plant propagation and optimal model for understanding the mechanisms of plant embryogenesis. In Panax ginseng, increasing studies have been widely performed to optimize the technology of S.E., while the underlying mechanism remains unclear. In this paper, we cloned and identified a WRKY family gene named PgWRKY6 which is upregulated in response to 2,4-D (2,4-dichlorophenoxyacetic acid)-induced embryogenic callus development. The silencing of PgWRKY6 obviously reduces the induction rate of embryogenic callus, indicating its crucial role in S.E. of Panax ginseng hairy root. The expressions of several ROS-scavenging genes are also inducible during embryogenic callus development, and the transcriptions of PgGST, PgAPX1, and PgSOD are demonstrated to be regulated by PgWRKY6. Recombinant PgWRKY6, an approximate 40-KDa protein purified from Escherichia coli, shows a specific DNA-binding activity with a potential recognition site of TTGAC(C/T). This work demonstrated that as a conserved WRKY family transcription factor, PgWRKY6 functions upstream of PgGST, PgAPX1, and PgSOD, and potentially mediated auxins -ROS signaling pathway in the process of S.E. in Panax species.

Global scale transcriptome analysis reveals differentially expressed genes involve in early somatic embryogenesis in Dimocarpus longan Lour

BACKGROUND

Somatic embryogenesis (SE) is a process of somatic cells that dedifferentiate to totipotent embryonic stem cells and generate embryos in vitro. Longan SE has been established and wildly used as model system for studying embryogenesis in woody plants, SE-related genes had been characterized. In spite of that, a comprehensive overview of SE at a molecular level is still absent. To understand the molecular mechanisms during longan SE, we examined the transcriptome changes by using Illumina HiSeq from the four distinct developmental stages, including non-embryogenic callus (NEC), embryogenic callus (EC), incomplete compact pro-embryogenic cultures (ICpEC), globular embryos (GE).

RESULTS

RNA-seq of the four samples generated a total of 243.78 million high quality reads, approximately 81.5% of the data were mapped to longan genome. The cDNA libraries of NEC, EC, ICpEC and GE, generated 22,743, 19,745, 21,144, 21,102 expressed transcripts, 1935, 1710, 1816, 1732 novel transcripts, 2645, 366, 505, 588 unique genes, respectively. Comparative transcriptome analysis showed that a total of 10,642, 4180, 5846 and 1785 genes were differentially expressed in the pairwise comparisons of NEC_vs_EC, EC_vs_ICpEC, EC_vs_GE, ICpEC_vs_GE, respectively. Among them, plant hormones signalling related genes were significantly enriched, especially the auxin and cytokinin signalling components. The transcripts of flavonoid biosynthesis related genes were mainly expressed in NEC, while fatty acid biosynthesis related genes mainly accumulated in early SE. In addition, the extracelluar protein encoding genes LTP, CHI, GLP, AGP, EP1 were related to longan SE. Combined with the FPKM value of longan nine tissues transcription, 27 SE specific or preferential genes (LEC1, LEC1-like, PDF1.3, GH3.6, AGL80, PIN1, BBM, WOX9, WOX2, ABI3, et al.) and 28 NEC preferential genes (LEA5, CNOT3, DC2.15, PR1-1, NsLTP2, DIR1, PIP1, PIP2.1, TIP2-1, POD-P7 and POD5 et al.) were characterized as molecular markers for longan early SE. qRT-PCR validation of SE-related genes showed a high correlation between RNA-seq and qRT-PCR data.

CONCLUSION

This study provides new insights into the role of the transcriptome during early SE in longan. Differentially expressed genes reveal that plant hormones signalling, flavonoid and fatty acid biosynthesis, and extracelluar protein related genes were involved in longan early SE. It could serve as a valuable platform resource for further functional studies addressing embryogenesis in woody plants.

Transcriptome analysis of the induction of somatic embryogenesis in Coffea canephora and the participation of ARF and Aux/IAA genes

Background

Somatic embryogenesis (SE) is a useful biotechnological tool to study the morpho-physiological, biochemical and molecular processes during the development of Coffea canephora. Plant growth regulators (PGR) play a key role during cell differentiation in SE. The Auxin-response-factor (ARF) and Auxin/Indole-3-acetic acid (Aux/IAA) are fundamental components involved in the signaling of the IAA. The IAA signaling pathway activates or represses the expression of genes responsive to auxins during the embryogenic transition of the somatic cells. The growing development of new generation sequencing technologies (NGS), as well as bioinformatics tools, has allowed us to broaden the landscape of SE study of various plant species and identify the genes directly involved.

Methods

Analysis of transcriptome expression profiles of the C. canephora genome and the identification of a particular set of differentially expressed genes (DEG) during SE are described in this study.

Results

A total of eight ARF and seven Aux/IAA differentially expressed genes were identified during the different stages of the SE induction process. The quantitative expression analysis showed that ARF18 and ARF5 genes are highly expressed after 21 days of the SE induction, while Aux/IAA7 and Aux/IAA12 genes are repressed.

Discussion

The results of this study allow a better understanding of the genes involved in the auxin signaling pathway as well as their expression profiles during the SE process.

Transcriptome-wide effect of DE-ETIOLATED1 (DET1) suppression in embryogenic callus of Carica papaya

Papaya is one of the most nutritional fruits, rich in vitamins, carotenoids, flavonoids and other antioxidants. Previous studies showed phytonutrient improvement without affecting quality in tomato fruit and rapeseed through the suppression of DE-ETIOLATED-1 (DET1), a negative regulator in photomorphogenesis. This study is conducted to study the effects of DET1 gene suppression in papaya embryogenic callus. Immature zygotic embryos were transformed with constitutive expression of a hairpin DET1 construct (hpDET1). PCR screening of transformed calli and reverse transcription quantitative PCR (RT-qPCR) verified that DET1 gene downregulation in two of the positive transformants. High-throughput cDNA 3' ends sequencing on DET1-suppressed and control calli for transcriptomic analysis of global gene expression identified a total of 452 significant (FDR < 0.05) differentially expressed genes (DEGs) upon DET1 suppression. The 123 upregulated DEGs were mainly involved in phenylpropanoid biosynthesis and stress responses, compared to 329 downregulated DEGs involved in developmental processes, lipid metabolism, and response to various stimuli. This is the first study to demonstrate transcriptome-wide relationship between light-regulated pathway and secondary metabolite biosynthetic pathways in papaya. This further supports that the manipulation of regulatory gene involved in light-regulated pathway is possible for phytonutrient improvement of tropical fruit crops.

Transcriptome analysis of callus from melon

OBJECTIVE

To identify the key genes promoting the differentiation of melon non-embryogenic callus into embryogenic callus.

METHODS

The transcriptome sequencing analysis was used to analyze the mRNA sequence in embryogenic callus (Z) and non-embryogenic callus (F); transcript mapping, gene expression analysis, cluster analysis, classification analysis and enrichment analysis were then used to detect the differentially expressed genes and enriched pathways.

RESULTS

The correlation coefficient between sample Z and sample F was 0.929 after transcript mapping. The overall gene expression levels in sample Z were higher as compared with sample F. Furthermore, cluster analysis showed that the expression of genes involved in photosynthesis was increased in sample Z when comparing to F. Besides, the classification of differential Gene Ontology (GO) showed that many metabolic processes were affected with the metabolism enhanced in embryogenic callus. Interestingly, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis further demonstrated the high metabolic activity and active secondary metabolite formation in the embryogenic callus.

CONCLUSION

The genes associated with photosynthesis, metabolic pathways and biosynthesis of secondary metabolites may promote the differentiation of callus into embryogenic callus.

Transcriptomics and co-expression networks reveal tissue-specific responses and regulatory hubs under mild and severe drought in papaya (Carica papaya L.)

Plants respond to drought stress through the ABA dependent and independent pathways, which in turn modulate transcriptional regulatory hubs. Here, we employed Illumina RNA-Seq to analyze a total of 18 cDNA libraries from leaves, sap, and roots of papaya plants under drought stress. Reference and de novo transcriptomic analyses identified 8,549 and 6,089 drought-responsive genes and unigenes, respectively. Core sets of 6 and 34 genes were simultaneously up- or down-regulated, respectively, in all stressed samples. Moreover, GO enrichment analysis revealed that under moderate drought stress, processes related to cell cycle and DNA repair were up-regulated in leaves and sap; while responses to abiotic stress, hormone signaling, sucrose metabolism, and suberin biosynthesis were up-regulated in roots. Under severe drought stress, biological processes related to abiotic stress, hormone signaling, and oxidation-reduction were up-regulated in all tissues. Moreover, similar biological processes were commonly down-regulated in all stressed samples. Furthermore, co-expression network analysis revealed three and eight transcriptionally regulated modules in leaves and roots, respectively. Seventeen stress-related TFs were identified, potentially serving as main regulatory hubs in leaves and roots. Our findings provide insight into the molecular responses of papaya plant to drought, which could contribute to the improvement of this important tropical crop.

Transcriptome analysis of Hevea brasiliensis in response to exogenous methyl jasmonate provides novel insights into regulation of jasmonate-elicited rubber biosynthesis

The phytohomorne methyl jasmonate (MeJA) is known to trigger extensive reprogramming of gene expression leading to transcriptional activation of many secondary metabolic pathways. However, natural rubber is a commercially important secondary metabolite and little is known about the genetic and genomic basis of jasmonate-elicited rubber biosynthesis in rubber tree (Hevea brasiliensis). RNA sequencing (RNA-seq) of H. brasiliensis bark treated with 1 g lanolin paste containing 0.02% w/w MeJA for 24 h (M2) and 0.04% w/w MeJA for 24 h (M4) was performed. A total of 2950 and 2850 differentially expressed genes in M2 and M4 compared with control (C) were respectively detected. Key genes involved in 2-C-methyl-D-erythritol 4-phosphate, rubber biosynthesis, glycolysis and carbon fixation (Calvin cycle) pathway were found to be up-regulated by MeJA treatment. Particularly, the expression of 3-hydroxy-3-metylglutaryl coenzyme A reductase in MVA pathway was down-regulated by MeJA treatment, but the expression of farnesyl diphosphate synthase (FPS) and cis-prenyltransferase (CPT, or rubber transferase) in rubber biosynthesis pathway were up-regulated by MeJA treatment. Up-regulation of critical genes in JA biosynthesis in response to MeJA treatment exhibited the self-activation of JA biosynthesis. In addition, up-regulated genes of great regulatory importance in cross-talk between JA and other hormone signaling, and of transcriptional regulation were identified. The increased expression levels of FPS and CPT in rubber biosynthesis pathway possibly resulted in an increased latex production in rubber tree treated with MeJA. The present results provide insights into the mechanism by which MeJA activates the rubber biosynthesis and the transcriptome data can also serve as the foundation for future research into the molecular basis for MeJA regulation of other cellular processes.

Advanced Proteomic Approaches to Elucidate Somatic Embryogenesis

Somatic embryogenesis (SE) is a cell differentiation process by which a somatic cell changes its genetic program and develops into an embryonic cell. Investigating this process with various explant sources in vitro has allowed us to trace somatic embryo development from germination to plantlets and has led to the generation of new technologies, including genetic transformation, endangered species conservation, and synthetic seed production. A transcriptome data comparison from different stages of the developing somatic embryo has revealed a complex network controlling the somatic cell's fate, suggesting that an interconnected network acts at the protein level. Here, we discuss the current progress on SE using proteomic-based data, focusing on changing patterns of proteins during the establishment of the somatic embryo. Despite the advanced proteomic approaches available so far, deciphering how the somatic embryo is induced is still in its infancy. The new proteomics techniques that lead to the quantification of proteins with different abundances during the induction of SE are opening this area of study for the first time. These quantitative differences can elucidate the different pathways involved in SE induction. We envisage that the application of these proteomic technologies can be pivotal to identifying proteins critical to the process of SE, demonstrating the cellular localization, posttranslational modifications, and turnover protein events required to switch from a somatic cell to a somatic embryo cell and providing new insights into the molecular mechanisms underlying SE. This work will help to develop biotechnological strategies for mass production of quality crop material.

Functional Genomics

Functional genomics encompasses diverse disciplines in molecular biology and bioinformatics to comprehend the blueprint, regulation, and expression of genetic elements that define the physiology of an organism. The deluge of sequencing data in the postgenomics era has demanded the involvement of computer scientists and mathematicians to create algorithms, analytical software, and databases for the storage, curation, and analysis of biological big data. In this chapter, we discuss on the concept of functional genomics in the context of systems biology and provide examples of its application in human genetic disease studies, molecular crop improvement, and metagenomics for antibiotic discovery. An overview of transcriptomics workflow and experimental considerations is also introduced. Lastly, we present an in-house case study of transcriptomics analysis of an aromatic herbal plant to understand the effect of elicitation on the biosynthesis of volatile organic compounds.