RNA-Seq SSRs of Moth Orchid and Screening for Molecular Markers across Genus Phalaenopsis (Orchidaceae)

De Novo Transcriptome Assembly of Anoectochilus roxburghii for Morphological Diversity Assessment and Potential Marker Development

Anoectochilus roxburghii is a rare and precious medicinal and ornamental plant of Orchidaceae. Abundant morphological characteristics have been observed among cultivated accessions. Our understanding of the genetic basis of morphological diversity is limited due to a lack of sequence data and candidate genes. In this study, a high-quality de novo transcriptome assembly of A.roxburghii was generated. A total of 138,385 unigenes were obtained, and a BUSCO (Benchmarking Universal Single-Copy Orthologs) analysis showed an assembly completeness of 98.8%. Multiple databases were used to obtain a comprehensive annotation, and the unigenes were functionally categorized using the GO (Gene Ontology), KOG (Eukaryotic Orthologous Groups), KEGG (Kyoto Encyclopedia of Genes and Genomes), and Nr databases. After comparing the phenotypic characteristics of five representative cultivars, a set of cultivar-specific, highly expressed unigenes was identified based on a comparative transcriptome analysis. Then, a WGCNA (Weighted Gene Co-expression Network Analysis) was performed to generate gene regulatory modules related to chlorophyll content (red) and sucrose synthase activity (black). In addition, the expression of six and four GO enrichment genes in the red and black modules, respectively, was analyzed using qRT-PCR to determine their putative functional roles in the leaves of the five cultivars. Finally, in silico SSR (Simple Sequence Repeat) mining of the assembled transcriptome identified 44,045 SSRs. Mononucleotide was the most dominant class of SSRs, followed by complex SSRs. In summary, this study reports on the phenomic and genomic resources of A. roxburghii, combining SSR marker development and validation. This report aids in morphological diversity assessments of Anoectochilus roxburghii.

Statistical Genomics Analysis of Simple Sequence Repeats from the Paphiopedilum Malipoense Transcriptome Reveals Control Knob Motifs Modulating Gene Expression

Simple sequence repeats (SSRs) are found in nonrandom distributions in genomes and are thought to impact gene expression. The distribution patterns of 48 295 SSRs of Paphiopedilum malipoense are mined and characterized based on the first full-length transcriptome and comprehensive transcriptome dataset from 12 organs. Statistical genomics analyses are used to investigate how SSRs in transcripts affect gene expression. The results demonstrate the correlations between SSR distributions, characteristics, and expression level. Nine expression-modulating motifs (expMotifs) are identified and a model is proposed to explain the effect of their key features, potency, and gene function on an intra-transcribed region scale. The expMotif-transcribed region combination is the most predominant contributor to the expression-modulating effect of SSRs, and some intra-transcribed regions are critical for this effect. Genes containing the same type of expMotif-SSR elements in the same transcribed region are likely linked in function, regulation, or evolution aspects. This study offers novel evidence to understand how SSRs regulate gene expression and provides potential regulatory elements for plant genetic engineering.

Biotechnological approaches for in vitro propagation, conservation and secondary metabolites production in Bulbophyllum, an endangered orchid genus: a review

Bulbophyllum represents the largest genus in the family Orchidaceae. The orchid species of this genus are widely used in the traditional medicine systems in different Asian countries such as China, India, Indonesia and Thailand. Studies on the secondary metabolites of Bulbophyllum have revealed the presence of important phytochemicals such as phenols, flavonoids, alkaloids, tannins, triterpenoids, sesquiterpenoids, steroids and glycosides. Some species of Bulbophyllum are reported to be of horticultural importance for their unique flowers. Habitat destruction and unsustainable utilization of different species of Bulbophyllum have led to a decline in the natural populations. The present review provides insights into the phytochemistry and ethnomedicinal uses of different species of Bulbophyllum, and highlights the biotechnological approaches developed for its conservation and sustainable utilization. Overall, the details provided in the present review can potentially be used for genome editing and biotechnological advances to develop plants with improved traits, which will be essential for the judicious utilization of the Bulbophyllum species so as to conserve and save the populations in the wild.

Transcriptome atlas of Phalaenopsis equestris

The vast diversity of Orchidaceae together with sophisticated adaptations to pollinators and other unique features make this family an attractive model for evolutionary and functional studies. The sequenced genome of Phalaenopsis equestris facilitates Orchidaceae research. Here, we present an RNA-seq-based transcriptome map of P. equestris that covers 19 organs of the plant, including leaves, roots, floral organs and the shoot apical meristem. We demonstrated the high quality of the data and showed the similarity of the P. equestris transcriptome map with the gene expression atlases of other plants. The transcriptome map can be easily accessed through our database Transcriptome Variation Analysis (TraVA) for visualizing gene expression profiles. As an example of the application, we analyzed the expression of Phalaenopsis “orphan” genes–those that do not have recognizable similarity with the genes of other plants. We found that approximately half of these genes were not expressed; the ones that were expressed were predominantly expressed in reproductive structures.

Development of SSR markers in Paeonia based on De Novo transcriptomic assemblies

Peony is a famous ornamental and medicinal plant in China, and peony hybrid breeding is an important means of germplasm innovation. However, research on the genome of this species is limited, thereby hindering the genetic and breeding research on peony. In the present study, simple sequence repeat (SSR) locus analysis was performed on expressed sequence tags obtained by the transcriptome sequencing of Paeonia using Microsatellite software. Primers with polymorphism were obtained via polymerase chain reaction amplification and electrophoresis. As a result, a total of 86,195 unigenes were obtained by assembling the transcriptome data of Paeonia. Functional annotations were obtained in seven functional databases including 49,172 (Non-Redundant Protein Sequence Database: 57.05%), 38,352 (Nucleotide Sequence Database: 44.49%), 36,477 (Swiss Prot: 42.32%), 38,905 (Clusters of Orthologous Groups for Eukaryotic Complete Genomes: 45.14%), 37,993 (Kyoto Encyclopedia of Genes and Genomes: 44.08%), 26,832 (Gene Ontology: 31.13%) and 37,758 (Pfam: 43.81%) unigenes. Meanwhile, 21,998 SSR loci were distributed in 17,567 unigenes containing SSR sequences, and the SSR distribution frequency was 25.52%, with an average of one SSR sequence per 4.66 kb. Mononucleotide, dinucleotide, and trinucleotide were the main repeat types, accounting for 55.74%, 25.58%, and 13.21% of the total repeat times, respectively. Forty-five pairs of the 100 pairs of primers selected randomly could amplify clear polymorphic bands. The polymorphic primers of these 45 pairs were used to cluster and analyze 16 species of peony. The new SSR molecular markers can be useful for the study of genetic diversity and marker-assisted breeding of peony.

Mining and Development of Novel SSR Markers Using Next Generation Sequencing (NGS) Data in Plants

Microsatellites, or simple sequence repeats (SSRs), are one of the most informative and multi-purpose genetic markers exploited in plant functional genomics. However, the discovery of SSRs and development using traditional methods are laborious, time-consuming, and costly. Recently, the availability of high-throughput sequencing technologies has enabled researchers to identify a substantial number of microsatellites at less cost and effort than traditional approaches. Illumina is a noteworthy transcriptome sequencing technology that is currently used in SSR marker development. Although 454 pyrosequencing datasets can be used for SSR development, this type of sequencing is no longer supported. This review aims to present an overview of the next generation sequencing, with a focus on the efficient use of de novo transcriptome sequencing (RNA-Seq) and related tools for mining and development of microsatellites in plants.

Screening transferable microsatellite markers across genus Phalaenopsis (Orchidaceae)

BACKGROUND

Molecular identification based on microsatellite loci is an important technology to improve the commercial breeding of the moth orchid. There are more than 30,000 cultivars have been enrolled at the Royal Horticultural Society (RHS). In this study, genomic microsatellite primer sets were developed from Phalaenopsis aphrodite subsp. formosana to further examine the transferability of across 21 Phalaenopsis species.

METHODS AND RESULTS

Twenty-eight polymorphic microsatellite markers were obtained using the magnetic bead enrichment method, with high transferability of the 21 species of the genus Phalaenopsis, especially in the subgenus Phalaenopsis. The 28 newly developed polymorphic microsatellite markers with high polymorphism information content values. The best and second fit grouping (K) are inferred as two and four by the ΔK evaluation in the assignment test. This result indicates that these microsatellite markers are discernible to subgenus Phalaenopsis.

CONCLUSIONS

Our results indicate that these new microsatellite markers are useful for delimiting species within genus Phalaenopsis. As expected, the genetic relationships between species of subgenus Phalaenopsis can be well distinguished based on the assignment test. These molecular markers could apply to assess the paternity of Phalaenopsis as well as investigating hybridization among species of genus Phalaenopsis.

Development of EST-SSR markers in flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) based on de novo transcriptomic assemblies

Flowering Chinese cabbage is one of the most important vegetable crops in southern China. Genetic improvement of various agronomic traits in this crop is underway to meet high market demand in the region, but the progress is hampered by limited number of molecular markers available in this crop. This study aimed to develop EST-SSR markers from transcriptome sequences generated by next-generation sequencing. RNA-seq of eight cabbage samples identified 48,975 unigenes. Of these unigenes, 23,267 were annotated in 56 gene ontology (GO) categories, 6,033 were mapped to 131 KEGG pathways, and 7,825 were assigned to clusters of orthologous groups (COGs). From the unigenes, 8,165 EST-SSR loci were identified and 98.57% of them were 1-3 nucleotide repeats with 14.32%, 41.08% and 43.17% of mono-, di- and tri-nucleotide repeats, respectively. Fifty-eight types of motifs were identified with A/T, AG/CT, AT/AT, AC/GT, AAG/CTT and AGG/CCT the most abundant. The lengths of repeated nucleotide sequences in all SSR loci ranged from 12 to 60 bp, with most (88.51%) under 20 bp. Among 170 primer pairs were randomly selected from a total of 4,912 SSR primers we designed, 48 yielded unambiguously polymorphic bands with high reproducibility. Cluster analysis using 48 SSRs classified 34 flowering Chinese cabbage cultivars into three groups. A large number of EST-SSR markers identified in this study will facilitate marker-assisted selection in the breeding programs of flowering Chinese cabbage.

Cutaneous transcriptome analysis in NIH hairless mice

Mice with spontaneous coat mutations are ideal animal models for studying skin development and tumorigenesis. In this study, skin hair growth cycle abnormalities were examined in NIH hairless mice 42 days after birth (P42) by using hematoxylin-eosin (H&E) staining. To examine the gene expression patterns in the skin of mutant mice, the dorsal skin of P42 female NIH mice and NIH hairless mice was sequenced by RNA-Seq, and 5,068 differentially expressed genes (DEGs) were identified (false discovery rate [FDR] ≥ 2, P < 0.05). A pathway analysis showed that basal cell carcinoma, the cell cycle and the Hippo, Hedgehog and Wnt signaling pathways were up-regulated in NIH hairless mice. Previous studies have shown that these pathways are closely associated with cell proliferation, cell cycle, organ size and cancer development. In contrast, signal transduction, bacterial and parasitic infection, and receptor-mediated pathways, including calcium signaling, were down-regulated in NIH hairless mice. A gene interaction network analysis was performed to identify genes related to hair follicle development. To verify the reliability of the RNA-Seq results, we used q-PCR to analyze 12 key genes identified from the gene interaction network analysis, including eight down-regulated and four up-regulated genes, and the results confirmed the reliability of the RNA-Seq results. Finally, we constructed the differential gene expression profiles of mutant mice by RNA-Seq. NIH hairless mice exhibited abnormalities in hair development and immune-related pathways. Pik3r1 and Pik3r3 were identified as key genes, laying the foundation for additional in-depth studies of hairless mice.

Molecular Basis Underlying Leaf Variegation of a Moth Orchid Mutant (Phalaenopsis aphrodite subsp. formosana)

Leaf variegation is often the focus of plant breeding. Here, we studied a variegated mutant of Phalaenopsis aphrodite subsp. formosana, which is usually used as a parent of horticultural breeding, to understand its anatomic and genetic regulatory mechanisms in variegation. Chloroplasts with well-organized thylakoids and starch grains were found only in the mesophyll cells of green sectors but not of yellow sectors, confirming that the variegation belongs to the chlorophyll type. The two-dimensional electrophoresis and LC/MS/MS also reveal differential expressions of PsbP and PsbO between the green and yellow leaf sectors. Full-length cDNA sequencing revealed that mutant transcripts were caused by intron retention. When conditioning on the total RNA expression, we found that the functional transcript of PsbO and mutant transcript of PsbP are higher expressed in the yellow sector than in the green sector, suggesting that the post-transcriptional regulation of PsbO and PsbP differentiates the performance between green and yellow sectors. Because PsbP plays an important role in the stability of thylakoid folding, we suggest that the negative regulation of PsbP may inhibit thylakoid development in the yellow sectors. This causes chlorophyll deficiency in the yellow sectors and results in leaf variegation. We also provide evidence of the link of virus CymMV and the formation of variegation according to the differential expression of CymMV between green and yellow sectors.

Direct LAMP Assay without Prior DNA Purification for Sex Determination of Papaya

Papaya (Carica papaya L.) is an economically important tropical fruit tree with hermaphrodite, male and female sex types. Hermaphroditic plants are the major type used for papaya production because their fruits have more commercial advantages than those of female plants. Sex determination of the seedlings, or during the early growth stages, is very important for the papaya seedling industry. Thus far, the only method for determining the sex type of a papaya at the seedling stage has been DNA analysis. In this study, a molecular technique—based on DNA analysis—was developed for detecting male-hermaphrodite-specific markers to examine the papaya’s sex type. This method is based on the loop-mediated isothermal amplification (LAMP) and does not require prior DNA purification. The results show that the method is an easy, efficient, and inexpensive way to determine a papaya’s sex. This is the first report on the LAMP assay, using intact plant materials-without DNA purification-as samples for the analysis of sex determination of papaya. We found that using high-efficiency DNA polymerase was essential for successful DNA amplification, using trace intact plant material as a template DNA source.

Characterization of Genomic Inheritance of Intergeneric Hybrids between Ascocenda and Phalaenopsis Cultivars by GISH, PCR-RFLP and RFLP

Background

The intergeneric hybrids between Ascocenda John De Biase ‘Blue’ and Phalaenopsis Chih Shang's Stripes have been generated to introduce the blue color into the Phalaenopsis germplasm in prior study. In order to confirm the inheritance in hybrid progenies, genomic in situ hybridization (GISH) and restriction fragment length polymorphism (RFLP) analysis were conducted to confirm the intergeneric hybridization status.

Methods/Results

GISH analysis showed the presence of both maternal and paternal chromosomes in the cells of the putative hybrids indicating that the putative hybrid seedlings were intergeneric hybrids of the two parents. Furthermore, twenty-seven putative hybrids were randomly selected for DNA analysis, and the external transcribed spacer (ETS) regions of nrDNA were analyzed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and RFLP analyses to identify the putative hybrids. RFLP analysis showed that the examined seedlings were intergeneric hybrids of the two parents. However, PCR-RFLP analysis showed bias to maternal genotype.

Conclusions

Both GISH and RFLP analyses are effective detection technology to identify the intergeneric hybridization status of putative hybrids. Furthermore, the use of PCR-RFLP analysis to identify the inheritance of putative hybrids should be carefully evaluated.