High-throughput sequencing discovery of conserved and novel microRNAs in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Comprehensive In Silico Characterization and Expression Pro-Filing of DA1/DAR Family Genes in Brassica rapa

The DA1/DAR family genes have been shown to play important roles in regulating organ size and plant biomass in the model plant Arabidopsis and several crops. However, this family has not been characterized in Brassica rapa (B. rapa). In this study, we identified 17 DA1&DAR genes from B. rapa. Phylogenetic analysis indicated that these genes are classified into four groups. Structural and motif analysis of BrDA1&DARs discovered that the genes within the same group have similar exon-intron structures and share an equal number of conserved motifs except for BrDAR6.3 from group IV, which contains two conserved motifs. Cis-regulatory elements identified four phytohormones (Salicylic acid, Abscisic acid, Gibberellin, and auxin) and three major abiotic (Light, Low temperature, and drought) responsive elements. Further, six br-miRNAs named br-miR164a, br-miR164b, br-miR164c, br-miR164d, br-miRN360, and br-miRN366 were found which target BrDAR6.1, BrDA1.4, and BrDA1.5. BrDA1&DAR genes were highly expressed in stem, root, silique, flower, leaf, and callus tissues. Moreover, qRT-PCR analyses indicated that some of these genes were responsive to abiotic stresses or phytohormone treatments. Our findings provide a foundation for further genetic and physiological studies of BrDA1&DARs in B. rapa.

Genome-wide miRNA analysis and integrated network for flavonoid biosynthesis in Osmanthus fragrans

Background

Osmanthus fragrans is an important economical plant containing multiple secondary metabolites including flavonoids and anthocyanins. During the past years, the roles of miRNAs in regulating the biosynthesis of secondary metabolites in plants have been widely investigated. However, few studies on miRNA expression profiles and the potential roles in regulating flavonoid biosynthesis have been reported in O. fragrans.

Results

In this study, we used high-throughput sequencing technology to analyze the expression profiles of miRNAs in leaf and flower tissues of O. fragrans. As a result, 106 conserved miRNAs distributed in 47 families and 88 novel miRNAs were identified. Further analysis showed there were 133 miRNAs differentially expressed in leaves and flowers. Additionally, the potential target genes of miRNAs as well as the related metabolic pathways were predicted. In the end, flavonoid content was measured in flower and leaf tissues and potential role of miR858 in regulating flavonoid synthesis was illustrated in O. fragrans.

Conclusions

This study not only provided the genome-wide miRNA profiles in the flower and leaf tissue of O. fragrans, but also investigated the potential regulatory role of miR858a in flavonoid synthesis in O. fragrans. The results specifically indicated the connection of miRNAs to the regulation of secondary metabolite biosynthesis in non-model economical plant.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07439-y.

miRNAs involved in transcriptome remodeling during pollen development and heat stress response in Solanum lycopersicum

Cellular transitions during development and stress response depend on coordinated transcriptomic and proteomic alterations. Pollen is particular because its development is a complex process that includes meiotic and mitotic divisions which causes a high heat sensitivity of these cells. Development and stress response are accompanied by a reprogramming of the transcriptome, e.g. by post-transcriptional regulation via miRNAs. We identified known and potentially novel miRNAs in the transcriptome of developing and heat-stressed pollen of Solanum lycopersicum (tomato). The prediction of target mRNAs yielded an equal number of predicted target-sites in CDS and 3'UTR regions of target mRNAs. The result enabled the postulation of a possible link between miRNAs and a fine-tuning of transcription factor abundance during pollen development. miRNAs seem to play a role in the pollen heat stress response as well. We identified several heat stress transcription factors and heat shock proteins as putative targets of miRNAs in response to heat stress, thereby placing these miRNAs as important elements of thermotolerance. Moreover, for members of the AP2, SBP and ARF family members we could predict a miRNA-mediated regulation during development via the miR172, mir156 and mir160-family strengthening the current concept of a cross-connection between development and stress response in plants.

Identification of Grafting-Responsive MicroRNAs Associated with Growth Regulation in Pecan [Carya illinoinensis (Wangenh.) K. Koch]

Pecan [Carya illinoinensis (Wangenh.) K. Koch] is an economically important nut tree and grafting is often used for clonal propagation of cultivars. However, there is a lack of research on the effects of rootstocks on scions, which are meaningful targets for directed breeding of pecan grafts. MicroRNAs (miRNAs) play an important role in many biological processes, but the mechanism underlying the involvement of miRNAs in grafting-conferred physiological changes is unclear. To identify the grafting-responsive miRNAs that may be involved in the regulation of growth in grafted pecan, six small RNA libraries were constructed from the phloem of two groups of grafts with significantly different growth performance on short and tall rootstocks. A total of 441 conserved miRNAs belonging to 42 miRNA families and 603 novel miRNAs were identified. Among the identified miRNAs, 24 (seven conserved and 17 novel) were significantly differentially expressed by the different grafts, implying that they might be responsive to grafting and potentially involved in the regulation of graft growth. Ninety-five target genes were predicted for the differentially expressed miRNAs; gene annotation was available for 33 of these. Analysis of their targets suggested that the miRNAs may regulate auxin transport, cell activity, and inorganic phosphate (Pi) acquisition, and thereby, mediate pecan graft growth. Use of the recently-published pecan genome enabled identification of a substantial population of miRNAs, which are now available for further research. We also identified the grafting-responsive miRNAs and their potential roles in pecan graft growth, providing a basis for research on long-distance regulation in grafted pecan.

Identification of conserved and novel miRNAs responsive to heat stress in flowering Chinese cabbage using high-throughput sequencing

Plant microRNAs (miRNAs) are noncoding and endogenous key regulators that play significant functions in regulating plant responses to stress, and plant growth and development. Heat stress is a critical abiotic stress that reduces the yield and quality of flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee). However, limited information is available on whether miRNAs are involved in the regulation of heat stress in B. campestris. A high-throughput sequencing approach was used to identify novel and conserved heat-responsive miRNAs in four small RNA libraries of flowering Chinese cabbage using leaves collected at 0 h, 1 h, 6 h and 12 h after a 38 °C heat-stress treatment. The analysis identified 41 conserved miRNAs (belonging to 19 MIR families), of which MIR156, MIR159, MIR168, MIR171 and MIR1885 had the most abundant molecules. Prediction and evaluation of novel miRNAs using the unannotated reads resulted in 18 candidate miRNAs. Differential expression analysis showed that most of the identified miRNAs were downregulated in heat-treated groups. To better understand functional importance, bioinformatic analysis predicted 432 unique putative target miRNAs involved in cells, cell parts, catalytic activity, cellular processes and abiotic stress responses. Furthermore, the Kyoto Encyclopedia of Genes and Genomes maps of flowering Chinese cabbage identified the significant role of miRNAs in stress adaptation and stress tolerance, and in several mitogen-activated protein kinases signaling pathways including cell death. This work presents a comprehensive study of the miRNAs for understanding the regulatory mechanisms and their participation in the heat stress of flowering Chinese cabbage.

Non-coding RNAs: Functional roles in the regulation of stress response in Brassica crops

Brassica crops face a combination of different abiotic and biotic stresses in the field that can reduce plant growth and development by affecting biochemical and morpho-physiological processes. Emerging evidence suggests that non-coding RNAs (ncRNAs), especially microRNAs (miRNAs) and long ncRNAs (lncRNAs), play a significant role in the modulation of gene expression in response to plant stresses. Recent advances in computational and experimental approaches are of great interest for identifying and functionally characterizing ncRNAs. While progress in this field is limited, numerous ncRNAs involved in the regulation of gene expression in response to stress have been reported in Brassica. In this review, we summarize the modes of action and functions of stress-related miRNAs and lncRNAs in Brassica as well as the approaches used to identify ncRNAs.

High-throughput sequencing reveals microRNAs in response to heat stress in the head kidney of rainbow trout (Oncorhynchus mykiss)

Recently, the research of animal microRNAs (miRNAs) has attracted wide attention for its regulatory effect in the development process and the response to abiotic stresses. Rainbow trout is a commercially and cold water fish species, and usually encounters heat stress, which affects its growth and leads to a huge economic loss. But there were few investigations about the roles of miRNAs in heat stress in rainbow trout. In this study, miRNAs of rainbow trout which were involved in heat stress were identified by high-throughput sequencing of six small RNA libraries from head kidney tissues under control (18 °C) and heat-treated (24 °C) conditions. A total of 392 conserved miRNAs and 989 novel miRNAs were identified, of which 78 miRNAs were expressed in different response to heat stress. Ten of these miRNAs were further validated by quantitative real-time PCR. In addition to, including 393 negative correlation miRNA-target gene pairs, several important regulatory pathways were involved in heat stress of the potential target genes, including protein processing in endoplasmic reticulum, NOD-like receptor signaling pathway, and phagosome. Our data significantly advance understanding of heat stress regulatory mechanism of miRNA in the head kidney of rainbow trout, which provide a useful resource for the cultivation of rainbow trout.

Genome-wide identification, expression profiling, and target gene analysis of microRNAs in the Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), vectors of tospoviruses (Bunyaviridae)

Thrips tabaci Lindeman is an important polyphagous insect pest species estimated to cause losses of more than U.S. $1 billion worldwide annually. Chemical insecticides are of limited use in the management of T. tabaci due to the thigmokinetic behavior and development of resistance to insecticides. There is an urgent need to find alternative management strategies. Small noncoding RNAs (sncRNAs) especially microRNAs (miRNAs) hold great promise as key regulators of gene expression in a wide range of organisms. MiRNAs are a group of endogenously originated sncRNA known to regulate gene expression in animals, plants, and protozoans. In this study, we explored these RNAs in T. tabaci using deep sequencing to provide a basis for future studies of their biological and physiological roles in governing gene expression. Apart from snoRNAs and piRNAs, our study identified nine novel and 130 known miRNAs from T. tabaci. Functional classification of the targets for these miRNAs predicted that majority are involved in regulating transcription, translation, signal transduction and genetic information processing. The higher expression of few miRNAs (such as tta-miR-281, tta-miR-184, tta-miR-3533, tta-miR-N1, tta-miR-N7, and tta-miR-N9) in T. tabaci pupal and adult stages reflected their possible role in larval and adult development, metamorphosis, parthenogenesis, and reproduction. This is the first exploration of the miRNAome in T. tabaci, which not only provides insights into their possible role in insect metamorphosis, growth, and development but also offer an important resource for future pest management strategies.

Characterization of Conserved and Novel microRNAs in Lilium lancifolium Thunb. by High-Throughput Sequencing

MicroRNAs (miRNAs) are among the class of noncoding small RNA molecules and play a crucial role in post-transcriptional regulation in plants. Although Lilium is one of the most popular ornamental flowers worldwide, however, there is no report on miRNAs identification. In the present study, therefore, miRNAs and their targets were identified from flower, leaf, bulblet and bulb of Lilium lancifolium Thunb. by high-throughput sequencing and bioinformatics analysis. In this study, a total of 38 conserved miRNAs belonging to 17 miRNA families and 44 novel miRNAs were identified. In total, 366 target genes for conserved miRNAs and 415 target genes for novel miRNAs were predicted. The majority of the target genes for conserved miRNAs were transcriptional factors and novel miRNAs targeted mainly protein coding genes. A total of 53 cleavage sites belonging to 6 conserved miRNAs families and 14 novel miRNAs were identified using degradome sequencing. Twenty-three miRNAs were randomly selected, then, their credibility was confirmed using northern blot or stem-loop qRT-PCR. The results from qRT-PCR analysis showed the expression pattern of 4 LL-miRNAs was opposite to their targets. Therefore, our finding provides an important basis to understand the biological functions of miRNAs in Lilium.

Genome-wide identification and expression analysis of calmodulin-like (CML) genes in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

BACKGROUND

Calmodulin-like (CML) proteins are a primary family of plant-specific Ca2+ sensors that specifically bind to Ca2+ and deliver a Ca2+ signal. CML proteins have been identified and characterized in many plant species, such as the model plant Arabidopsis and rice. Based on considerable evidence, the roles of CML proteins are crucial in plant growth and development and in the response to various external stimuli. Nevertheless, the characterization and expression profiling of CML genes in Chinese cabbage (Brassica rapa L. ssp. pekinensis) remain limited.

RESULTS

In this study, a genome-wide search and comprehensive analysis were performed, and a total of 79 BrCML genes were identified in Chinese cabbage. Gene structure analysis revealed that these BrCML genes contained two to four conserved EF-hand motifs. Phylogenetic analysis showed that CML homologs between Chinese cabbage and Arabidopsis shared close relationships. The identified BrCML genes were located across ten chromosomes and three different subgenomes of Chinese cabbage. Moreover, 126 pairs of orthologous CML genes were found among Chinese cabbage, Arabidopsis and Brassica oleracea. Expression analysis revealed that the expression of some BrCML genes was tissue-specific and that of some was susceptible to temperature stress. A putative interaction network of BrCML proteins was proposed, which suggested that BrCML2, BrCML6, BrCML15 and BrCML25 were co-expressed and might play roles in flower development and other relevant biological processes of Chinese cabbage.

CONCLUSIONS

The results of this study increased the understanding and characterization of BrCML genes in Chinese cabbage, and will be a rich resource for further studies to investigate BrCML protein function in various developmental processes of Chinese cabbage.

Identification and characterization of microRNAs in Humulus lupulus using high-throughput sequencing and their response to Citrus bark cracking viroid (CBCVd) infection

BACKGROUND

Hop (Humulus lupulus L.) plants are grown primarily for the brewing industry and have been used as a traditional medicinal herb for a long time. Severe hop stunt disease caused by the recently discovered Citrus bark cracking viroid (CBCVd) is one of the most devastating diseases among other viroid infections in hop. MicroRNAs (miRNAs) are a class of non-coding small RNAs that play important roles in gene expression regulation. To identify miRNAs in hop and their response to CBCVd-infection, two small RNA (sRNA) libraries were prepared from healthy and CBCVd-infected hop plants and were investigated by high throughput sequencing.

RESULTS

A total of 67 conserved and 49 novel miRNAs were identified. Among them, 36 conserved and 37 novel miRNAs were found to be differentially recovered in response to CBCVd-infection. A total of 311 potential targets was predicted for conserved and novel miRNAs based on a sequence homology search using hop transcriptome data. The majority of predicted targets significantly belonged to transcriptional factors that may regulate hop leaf, root and cone growth and development. In addition, the identified miRNAs might also play an important roles in other cellular and metabolic processes, such as signal transduction, stress response and other physiological processes, including prenylflavonoid biosynthesis pathways. Quantitative real time PCR analysis of selected targets revealed their negative correlation with their corresponding CBCVd-responsive miRNAs.

CONCLUSIONS

Based on the results, we concluded that CBCVd-responsive miRNAs modulate several hormone pathways and transcriptional factors that play important roles in the regulation of metabolism, growth and development. These results provide a framework for further analysis of regulatory roles of sRNAs in plant defense mechanism including other hop infecting viroids in particular.

Identification of anthocyanin biosynthesis related microRNAs in a distinctive Chinese radish (Raphanus sativus L.) by high-throughput sequencing

Anthocyanins are widely distributed water-soluble phytochemical pigments belonging to the flavonoid group. To date, limited knowledge is available about the regulatory roles of miRNAs in anthocyanin biosynthesis in plants. To identify the miRNAs associated with anthocyanin biosynthesis in radish, five small RNA (sRNA) libraries constructed from 'Xinlimei' radish roots at 11, 21, 44, 56 and 73 days (d) were examined using high-throughput sequencing technology. A total of 102.02 million (M) clean reads were generated, from which 483 known and 1415 novel miRNAs were identified. Combined with target prediction and annotation, 72 differentially expressed miRNAs (52 known and 20 novel miRNAs) were more likely to participate in anthocyanin biosynthesis. Several target genes for these miRNAs encode a few transcription factors, including Myb domain (MYB), basic helix-loop-helix (bHLH), WD40 repeat, squamosa promoter binding protein like (SPL), auxin response factor (ARF), ethylene insensitive 3 (EIN3), WRKY and MADS-box proteins. Furthermore, the expression patterns of some anthocyanin biosynthesis related miRNAs and their corresponding targets were validated by RT-qPCR. Based on the characterization of anthocyanin biosynthesis related miRNAs and their target genes, a putative miRNA-target module regulating anthocyanin biosynthesis was proposed. This study represents the first genome-wide identification of miRNAs associated with anthocyanin biosynthesis in radish, and provides insights into the molecular mechanisms underlying regulation of anthocyanin biosynthesis in radish and other crops.

Genome-Wide Identification and Characterization of MicroRNAs and Target Genes in Lonicera japonica

MiRNAs function in post-transcriptional regulation of gene expression and play very important roles in plant development. Lonicera japonica is one of the important medicinal plants in China. However, few studies on the discovery of conserved and novel miRNAs from L. japonica were reported. In this study, we employed deep sequencing technology to identify miRNAs in leaf and flower tissues of L. japonica. A total of 22.97 million clean reads from flower and leaf tissues were obtained, which generated 146 conserved miRNAs distributed in 20 families and 110 novel miRNAs. Accordingly, 72 differentially expressed miRNAs (P≤0.001) between leaves and flowers and their potential target genes were identified and validated. The qRT-PCR validation showed that majority of the differentially expressed miRNAs showed significant tissue-specific expression in L. japonica. Furthermore, the miRNA-mRNA and mRNA-mRNA regulatory networks were constructed using Cytoscape software. Taken together, this study identified a large number of miRNAs and target genes in L. japonica, which not only provides the first global miRNA expression profiles, but also sheds light on functional genomics research on L. japonica in the future.

The First Report of miRNAs from a Thysanopteran Insect, Thrips palmi Karny Using High-Throughput Sequencing

Thrips palmi Karny (Thysanoptera: Thripidae) is the sole vector of Watermelon bud necrosis tospovirus, where the crop loss has been estimated to be around USD 50 million annually. Chemical insecticides are of limited use in the management of T. palmi due to the thigmokinetic behaviour and development of high levels of resistance to insecticides. There is an urgent need to find out an effective futuristic management strategy, where the small RNAs especially microRNAs hold great promise as a key player in the growth and development. miRNAs are a class of short non-coding RNAs involved in regulation of gene expression either by mRNA cleavage or by translational repression. We identified and characterized a total of 77 miRNAs from T. palmi using high-throughput deep sequencing. Functional classifications of the targets for these miRNAs revealed that majority of them are involved in the regulation of transcription and translation, nucleotide binding and signal transduction. We have also validated few of these miRNAs employing stem-loop RT-PCR, qRT-PCR and Northern blot. The present study not only provides an in-depth understanding of the biological and physiological roles of miRNAs in governing gene expression but may also lead as an invaluable tool for the management of thysanopteran insects in the future.

Identification of microRNAs and Their Target Genes Explores miRNA-Mediated Regulatory Network of Cytoplasmic Male Sterility Occurrence during Anther Development in Radish (Raphanus sativus L.)

MicroRNAs (miRNAs) are a type of endogenous non-coding small RNAs that play critical roles in plant growth and developmental processes. Cytoplasmic male sterility (CMS) is typically a maternally inherited trait and widely used in plant heterosis utilization. However, the miRNA-mediated regulatory network of CMS occurrence during anther development remains largely unknown in radish. In this study, a comparative small RNAome sequencing was conducted in floral buds of CMS line 'WA' and its maintainer line 'WB' by high-throughput sequencing. A total of 162 known miRNAs belonging to 25 conserved and 24 non-conserved miRNA families were isolated and 27 potential novel miRNA families were identified for the first time in floral buds of radish. Of these miRNAs, 28 known and 14 potential novel miRNAs were differentially expressed during anther development. Several target genes for CMS occurrence-related miRNAs encode important transcription factors and functional proteins, which might be involved in multiple biological processes including auxin signaling pathways, signal transduction, miRNA target silencing, floral organ development, and organellar gene expression. Moreover, the expression patterns of several CMS occurrence-related miRNAs and their targets during three stages of anther development were validated by qRT-PCR. In addition, a potential miRNA-mediated regulatory network of CMS occurrence during anther development was firstly proposed in radish. These findings could contribute new insights into complex miRNA-mediated genetic regulatory network of CMS occurrence and advance our understanding of the roles of miRNAs during CMS occurrence and microspore formation in radish and other crops.

Identification of Rapeseed MicroRNAs Involved in Early Stage Seed Germination under Salt and Drought Stresses

Drought and salinity are severe and wide-ranging abiotic stresses that substantially affect crop germination, development and productivity, and seed germination is the first critical step in plant growth and development. To comprehensively investigate small-RNA targets and improve our understanding of miRNA-mediated post-transcriptional regulation networks during Brassica napus seed imbibition under drought and salt stresses, we constructed three small-RNA libraries from B. napus variety ZS11 embryos exposed to salt (200 mM NaCl, denoted "S"), drought (200 g L(-1) PEG-6000, denoted "D"), and distilled water (denoted "CK") during imbibition and sequenced them using an Illumina Genome Analyzer. A total of 11,528,557, 12,080,081, and 12,315,608 raw reads were obtained from the CK, D, and S libraries, respectively. Further analysis identified 85 known miRNAs belonging to 31 miRNA families and 882 novel miRNAs among the three libraries. Comparison of the D and CK libraries revealed significant down-regulation of six miRNA families, miR156, miR169, miR860, miR399, miR171, and miR395, whereas only miR172 was significantly up-regulated. In contrast, comparison of the S library with the CK library showed significant down-regulation of only two miRNA families: miRNA393 and miRNA399. Putative targets for 336, 376, and 340 novel miRNAs were successfully predicted in the CK, D, and S libraries, respectively, and 271 miRNA families and 20 target gene families [including disease resistance protein (DIRP), drought-responsive family protein (DRRP), early responsive to dehydration stress protein (ERD), stress-responsive alpha-beta barrel domain protein (SRAP), and salt tolerance homolog2 (STH2)] were confirmed as being core miRNAs and genes involved in the seed imbibition response to salt and drought stresses. The sequencing results were partially validated by quantitative RT-PCR for both conserved and novel miRNAs as well as the predicted target genes. Our data suggest that diverse and complex miRNAs are involved in seed imbibition, indicating that miRNAs are involved in plant hormone regulation, and may play important roles during seed germination under salt- or drought-stress conditions.

Impacts of Whole-Genome Triplication on MIRNA Evolution in Brassica rapa

MicroRNAs (miRNAs) are a class of short non-coding, endogenous RNAs that play essential roles in eukaryotes. Although the influence of whole-genome triplication (WGT) on protein-coding genes has been well documented in Brassica rapa, little is known about its impacts on MIRNAs. In this study, through generating a comprehensive annotation of 680 MIRNAs for B. rapa, we analyzed the evolutionary characteristics of these MIRNAs from different aspects in B. rapa. First, while MIRNAs and genes show similar patterns of biased distribution among subgenomes of B. rapa, we found that MIRNAs are much more overretained than genes following fractionation after WGT. Second, multiple-copy MIRNAs show significant sequence conservation than that of single-copy MIRNAs, which is opposite to that of genes. This indicates that increased purifying selection is acting upon these highly retained multiple-copy MIRNAs and their functional importance over singleton MIRNAs. Furthermore, we found the extensive divergence between pairs of miRNAs and their target genes following the WGT in B. rapa. In summary, our study provides a valuable resource for exploring MIRNA in B. rapa and highlights the impacts of WGT on the evolution of MIRNA.

Integrative Analysis of mRNA and miRNA Expression Profiles of the Tuberous Root Development at Seedling Stages in Turnips

The tuberous root of Brassica rapa L. (turnip) is an important modified organ for nutrition storage. A better understanding of the molecular mechanisms involved in the process of tuberous root development is of great value in both economic and biological context. In this study, we analyzed the expression profiles of both mRNAs and miRNAs in tuberous roots at an early stage before cortex splitting (ES), cortex splitting stage (CSS), and secondary root thickening stage (RTS) in turnip based on high-throughput sequencing technology. A large number of differentially expressed genes (DEGs) and several differentially expressed miRNAs (DEMs) were identified. Based on the DEG analysis, we propose that metabolism is the dominant pathway in both tuberous root initiation and secondary thickening process. The plant hormone signal transduction pathway may play a predominant role in regulating tuberous root initiation, while the starch and sucrose metabolism may be more important for the secondary thickening process. These hypotheses were partially supported by sequential DEM analyses. Of all DEMs, miR156a, miR157a, and miR172a exhibited relatively high expression levels, and were differentially expressed in both tuberous root initiation and the secondary thickening process with the expression profiles negatively correlated with those of their target genes. Our results suggest that these miRNAs play important roles in tuberous root development in turnips.

Transcriptome-wide analysis of chromium-stress responsive microRNAs to explore miRNA-mediated regulatory networks in radish (Raphanus sativus L.)

MicroRNAs (miRNAs) are small noncoding RNAs that play pivotal roles in plant growth, development and stress response. Chromium (Cr) is one of common environmental contaminants possessing potential health hazards to living organisms. To date, little is known about the regulatory roles of miRNAs in response to Cr stress in radish. To systematically identify Cr-responsive miRNAs and their targets in radish, two sRNA libraries derived from Cr-free (CK) and Cr-treated (Cr200) roots were constructed. With Solexa sequencing, 81 known and 72 novel miRNAs were identified, from which 54 known and 16 novel miRNAs were significantly differentially expressed under Cr stress. Several target genes for Cr-responsive miRNAs encode different transcription factor (TF) families, including SPLs, MYBs, ERFs and bZIPs, might regulate corresponding HM-related transcriptional processes in plants. Notably, a few key responsive enzymes or proteins, including HMA, YSL1 and ABC transporter protein were involved in Cr uptake and homeostasis process. Furthermore, the expression patterns of some Cr-responsive miRNAs and their targets were validated by RT-qPCR. This study represents the first characterization of Cr-responsive miRNAs and their targets in radish. The outcomes of this study could provide novel insights into miRNA-mediated regulatory mechanisms underlying plant response to Cr stress in root vegetable crops.

Identification and characterization of microRNAs expressed in human breast cancer chemo-resistant MCF-7/Adr cells by Solexa deep-sequencing technology

BACKGROUND/AIM

Breast cancer is the most common type of tumor in female and chemoresistance has been a major clinical obstacle to the treatment in clinical patients. miRNA was one of the factors demonstrated to play certain roles in chemoesistance in breast cancer. In this study, we exploited Solexa deep sequencing technology to identify differentially expressed miRNA from samples in vitro, trying to find novel relationship between miRNA and chemoresistance in breast cancer.

METHODS

The human breast cancer MCF-7 cell line was pulse-selected with doxorubicin (10 pulses, once a week for 4h, with 1μM doxorubicin) to generate MCF-7/Adr cells. Total RNA was extracted from the treated and untreated MCF-7 cells and subsequently subjected to real time PCR. Two small RNA libraries of MCF7NON and MCF7ADR were established to record the Solexa sequencing results of the PCR products above. All the sequencing results were verified by Stem-loop real-time PCR. GO annotation and KEGG analysis program were exploited to enrich the differentially expressed miRNAs.

RESULTS

The results showed that 214,822 and 378,597 reads were mapped in the MCF7ADR and MCF7NON libraries when aligned to hairpin structure respectively. Meanwhile, 1323 and 520 reads were mapped when aligned to mature sequences. In addition, 310 known mature miRNAs were coexpressed in both libraries. Comparing the MCF7ADR group to the MCF7NON group, 18 miRNAs were significantly differentially expressed. GO annotation and KEGG analysis showed that the target genes were enriched in regulation of transcription and development as well as Wnt signaling pathway, MAPK signaling pathway and TGF-ß signaling pathway.

CONCLUSION

The results proved that the Solexa deep sequencing was a powerful and reliable platform to analyze small RNAs. And further investigation should be conducted for the biological process and pathways that have been identified and more efforts should be made to research the mechanism of chemoresistance in breast cancer.

The elucidation of stress memory inheritance in Brassica rapa plants

Plants are able to maintain the memory of stress exposure throughout their ontogenesis and faithfully propagate it into the next generation. Recent evidence argues for the epigenetic nature of this phenomenon. Small RNAs (smRNAs) are one of the vital epigenetic factors because they can both affect gene expression at the place of their generation and maintain non-cell-autonomous gene regulation. Here, we have made an attempt to decipher the contribution of smRNAs to the heat-shock-induced transgenerational inheritance in Brassica rapa plants using sequencing technology. To do this, we have generated comprehensive profiles of a transcriptome and a small RNAome (smRNAome) from somatic and reproductive tissues of stressed plants and their untreated progeny. We have demonstrated that the highest tissue-specific alterations in the transcriptome and smRNAome profile are detected in tissues that were not directly exposed to stress, namely, in the endosperm and pollen. Importantly, we have revealed that the progeny of stressed plants exhibit the highest fluctuations at the smRNAome level but not at the transcriptome level. Additionally, we have uncovered the existence of heat-inducible and transgenerationally transmitted tRNA-derived small RNA fragments in plants. Finally, we suggest that miR168 and braAGO1 are involved in the stress-induced transgenerational inheritance in plants.

Identification and characterization of cold-responsive microRNAs in tea plant (Camellia sinensis) and their targets using high-throughput sequencing and degradome analysis

BACKGROUND

MicroRNAs (miRNAs) are approximately 19 ~ 21 nucleotide noncoding RNAs produced by Dicer-catalyzed excision from stem-loop precursors. Many plant miRNAs have critical functions in development, nutrient homeostasis, abiotic stress responses, and pathogen responses via interaction with specific target mRNAs. Camellia sinensis is one of the most important commercial beverage crops in the world. However, miRNAs associated with cold stress tolerance in C. sinensis remains unexplored. The use of high-throughput sequencing can provide a much deeper understanding of miRNAs. To obtain more insight into the function of miRNAs in cold stress tolerance, Illumina sequencing of C. sinensis sRNA was conducted.

RESULT

Solexa sequencing technology was used for high-throughput sequencing of the small RNA library from the cold treatment of tea leaves. To align the sequencing data with known plant miRNAs, we characterized 106 conserved C. sinensis miRNAs. In addition, 215 potential candidate miRNAs were found, among, which 98 candidates with star sequences were chosen as novel miRNAs. Both congruously and differentially regulated miRNAs were obtained, and cultivar-specific miRNAs were identified by microarray-based hybridization in response to cold stress. The results were also confirmed by quantitative real-time polymerase chain reaction. To confirm the targets of miRNAs, two degradome libraries from two treatments were constructed. According to degradome sequencing, 455 and 591 genes were identified as cleavage targets of miRNAs from cold treatments and control libraries, respectively, and 283 targets were present in both libraries. Functional analysis of these miRNA targets indicated their involvement in important activities, such as development, regulation of transcription, and stress response.

CONCLUSIONS

We discovered 31 up-regulated miRNAs and 43 down-regulated miRNAs in 'Yingshuang', and 46 up-regulated miRNA and 45 down-regulated miRNAs in 'Baiye 1' in response to cold stress, respectively. A total of 763 related target genes were detected by degradome sequencing. The RLM-5'RACE procedure was successfully used to map the cleavage sites in six target genes of C. sinensis. These findings reveal important information about the regulatory mechanism of miRNAs in C. sinensis, and promote the understanding of miRNA functions during the cold response. The miRNA genotype-specific expression model might explain the distinct cold sensitivities between tea lines.

Identification of the conserved and novel miRNAs in Mulberry by high-throughput sequencing

miRNAs are a class of non-coding endogenous small RNAs. They play vital roles in plant growth, development, and response to biotic and abiotic stress by negatively regulating genes. Mulberry trees are economically important species with multiple uses. However, to date, little is known about mulberry miRNAs and their target genes. In the present study, three small mulberry RNA libraries were constructed and sequenced using high-throughput sequencing technology. Results showed 85 conserved miRNAs belonging to 31 miRNA families and 262 novel miRNAs at 371 loci. Quantitative real-time PCR (qRT-PCR) analysis confirmed the expression pattern of 9 conserved and 5 novel miRNAs in leaves, bark, and male flowers. A total of 332 potential target genes were predicted to be associated with these 113 novel miRNAs. These results provide a basis for further understanding of mulberry miRNAs and the biological processes in which they are involved.

High-throughput sequence analysis of small RNAs in skotomorphogenic seedlings of Brassica rapa ssp. rapa

Skotomorphogenic development is the process by which seedlings adapt to a stressful dark environment. Such metabolic responses to abiotic stresses in plants are known to be regulated in part by microRNAs (miRNAs); however, little is known about the involvement of miRNAs in the regulation of skotomorphogenesis. To identify miRNAs at the genome-wide level in skotomorphogenic seedlings of turnip (Brassica rapa subsp. rapa), an important worldwide root vegetable, we used Solexa sequencing to sequence a small RNA library from seedlings grown in the dark for 4 days. Deep sequencing showed that the small RNAs (sRNAs) were predominantly 21 to 24 nucleotides long. Specifically, 13,319,035 reads produced 359,531 unique sRNAs including rRNA, tRNA, miRNA, small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), and unannotated sRNAs. Sequence analysis identified 96 conserved miRNAs belonging to 36 miRNA families and 576 novel miRNAs. qRT-PCR confirmed that the miRNAs were expressed during skotomorphogenesis similar to the trends shown by the Solexa sequencing results. A total of 2013 potential targets were predicted, and the targets of BrmiR157, BrmiR159 and BrmiR160 were proved to be regulated by miRNA-guided cleavage. These results show that specific regulatory miRNAs are present in skotomorphogenic seedlings of turnip and may play important roles in growth, development, and response to dark environment.

A genome-wide perspective of miRNAome in response to high temperature, salinity and drought stresses in Brassica juncea (Czern) L

Micro RNAs (miRNAs) are involved in diverse biological processes including adaptive response towards abiotic stresses. To unravel small RNAs and more specifically miRNAs that can potentially regulate determinants of abiotic stress tolerance, next generation sequencing of B. juncea seedlings subjected to high temperature, high salt and drought conditions was carried out. With the help of UEA sRNA workbench software package, 51 conserved miRNAs belonging to 30 miRNA families were identified. As there was limited genomic information available for B. juncea, we generated and assembled its genome sequence at a low coverage. Using the generated sequence and other publically available Brassica genomic/transcriptomic resources as mapping reference, 126 novel (not reported in any plant species) were discovered for the first time in B. juncea. Further analysis also revealed existence of 32 and 37 star sequences for conserved and novel miRNAs, respectively. The expression of selected conserved and novel miRNAs under conditions of different abiotic stresses was revalidated through universal TaqMan based real time PCR. Putative targets of identified conserved and novel miRNAs were predicted in B. rapa to gain insights into functional roles manifested by B. juncea miRNAs. Furthermore, SPL2-like, ARF17-like and a NAC domain containing protein were experimentally validated as targets of miR156, miR160 and miR164 respectively. Investigation of gene ontologies linked with targets of known and novel miRNAs forecasted their involvement in various biological functions.

A contig-based strategy for the genome-wide discovery of microRNAs without complete genome resources

MicroRNAs (miRNAs) are important regulators of many cellular processes and exist in a wide range of eukaryotes. High-throughput sequencing is a mainstream method of miRNA identification through which it is possible to obtain the complete small RNA profile of an organism. Currently, most approaches to miRNA identification rely on a reference genome for the prediction of hairpin structures. However, many species of economic and phylogenetic importance are non-model organisms without complete genome sequences, and this limits miRNA discovery. Here, to overcome this limitation, we have developed a contig-based miRNA identification strategy. We applied this method to a triploid species of edible banana (GCTCV-119, Musa spp. AAA group) and identified 180 pre-miRNAs and 314 mature miRNAs, which is three times more than those were predicted by the available dataset-based methods (represented by EST+GSS). Based on the recently published miRNA data set of Musa acuminate, the recall rate and precision of our strategy are estimated to be 70.6% and 92.2%, respectively, significantly better than those of EST+GSS-based strategy (10.2% and 50.0%, respectively). Our novel, efficient and cost-effective strategy facilitates the study of the functional and evolutionary role of miRNAs, as well as miRNA-based molecular breeding, in non-model species of economic or evolutionary interest.

Applications and challenges of next-generation sequencing in Brassica species

Next-generation sequencing (NGS) produces numerous (often millions) short DNA sequence reads, typically varying between 25 and 400 bp in length, at a relatively low cost and in a short time. This revolutionary technology is being increasingly applied in whole-genome, transcriptome, epigenome and small RNA sequencing, molecular marker and gene discovery, comparative and evolutionary genomics, and association studies. The Brassica genus comprises some of the most agro-economically important crops, providing abundant vegetables, condiments, fodder, oil and medicinal products. Many Brassica species have undergone the process of polyploidization, which makes their genomes exceptionally complex and can create difficulties in genomics research. NGS injects new vigor into Brassica research, yet also faces specific challenges in the analysis of complex crop genomes and traits. In this article, we review the advantages and limitations of different NGS technologies and their applications and challenges, using Brassica as an advanced model system for agronomically important, polyploid crops. Specifically, we focus on the use of NGS for genome resequencing, transcriptome sequencing, development of single-nucleotide polymorphism markers, and identification of novel microRNAs and their targets. We present trends and advances in NGS technology in relation to Brassica crop improvement, with wide application for sophisticated genomics research into agronomically important polyploid crops.

High-throughput sequencing identification of novel and conserved miRNAs in the Brassica oleracea leaves

Background

Plant microRNAs are short (~21 nt) non-coding molecules that regulate gene expression by targeting the mRNA cleavage or protein translation inhibition. In this manner, they play many important roles in the cells of living organisms. One of the plant species in which the entire set of miRNAs has not been yet completely identified is Brassica oleracea var. capitata (cabbage). For this reason and for the economic and nutritional importance of this food crop, high-throughput small RNAs sequencing has been performed to discover the novel and conserved miRNAs in mature cabbage leaves.

Results

In this study, raw reads generated from three small RNA libraries were bioinformatically processed and further analyzed to select sequences homologous to known B. oleracea and other plant miRNAs. As a result of this analysis, 261 conserved miRNAs (belonging to 62 families) have been discovered. MIR169, MIR167 and MIR166 were the largest miRNA families, while the highest abundance molecules were miR167, miR166, miR168c and miR157a. Among the generated sequencing reads, miRNAs* were also found, such as the miR162c*, miR160a* and miR157a*. The unannotated tags were used in the prediction and evaluation of novel miRNAs, which resulted in the 26 potential miRNAs proposal. The expressions of 13 selected miRNAs were analyzed by northern blot hybridization. The target prediction and annotation for identified miRNAs were performed, according to which discovered molecules may target mRNAs encoding several potential proteins – e.g., transcription factors, polypeptides that regulate hormone stimuli and abiotic stress response, and molecules participating in transport and cell communication. Additionally, KEGG maps analysis suggested that the miRNAs in cabbage are involved in important processing pathways, including glycolysis, glycerolipid metabolism, flavonoid biosynthesis and oxidative phosphorylation.

Conclusions

Conclusively, for the first time, the large set of miRNAs was identified in mature cabbage leaves. Potential targets designation for these miRNAs may suggest their essential role in many plants primary biological processes. Presented study not only supplements the knowledge about B. oleracea miRNAs, but additionally it may be used in other research concerning the improvement of the cabbage cultivation.

Trans-acting small interfering RNA4: key to nutraceutical synthesis in grape development?

The facility and versatility of microRNAs (miRNAs) to evolve and change likely underlies how they have become dominant constituents of eukaryotic genomes. In this opinion article I propose that trans-acting small interfering RNA gene 4 (TAS4) evolution may be important for biosynthesis of polyphenolics, arbuscular symbiosis, and bacterial pathogen etiologies. Expression-based and phylogenetic evidence shows that TAS4 targets two novel grape (Vitis vinifera L.) MYB transcription factors (VvMYBA6, VvMYBA7) that spawn phased small interfering RNAs (siRNAs) which probably function in nutraceutical bioflavonoid biosynthesis and fruit development. Characterization of the molecular mechanisms of TAS4 control of plant development and integration into biotic and abiotic stress- and nutrient-signaling regulatory networks has applicability to molecular breeding and the development of strategies for engineering healthier foods.

Transcriptome-wide identification and characterization of microRNAs from castor bean (Ricinus communis L.)

BACKGROUND

MicroRNAs (miRNAs) are endogenously encoded small RNAs that post-transcriptionally regulate gene expression and play essential roles in numerous developmental and physiological processes. Currently, little information on the transcriptome and tissue-specific expression of miRNAs is available in the model non-edible oilseed crop castor bean (Ricinus communis L.), one of the most important non-edible oilseed crops cultivated worldwide. Recent advances in sequencing technologies have allowed the identification of conserved and novel miRNAs in many plant species. Here, we used high-throughput sequencing technologies to identify and characterize the miRNAs in castor bean.

RESULTS

Five small RNA libraries were constructed for deep sequencing from root tips, leaves, developing seeds (at the initial stage, seed1; and at the fast oil accumulation stage, seed2) and endosperms in castor bean. High-throughput sequencing generated a large number of sequence reads of small RNAs in this study. In total, 86 conserved miRNAs were identified, including 63 known and 23 newly identified. Sixteen miRNA isoform variants in length were found from the conserved miRNAs of castor bean. MiRNAs displayed diverse organ-specific expression levels among five libraries. Combined with criteria for miRNA annotation and a RT-PCR approach, 72 novel miRNAs and their potential precursors were annotated and 20 miRNAs newly identified were validated. In addition, new target candidates for miRNAs newly identified in this study were proposed.

CONCLUSIONS

The current study presents the first high-throughput small RNA sequencing study performed in castor bean to identify its miRNA population. It characterizes and increases the number of miRNAs and their isoforms identified in castor bean. The miRNA expression analysis provides a foundation for understanding castor bean miRNA organ-specific expression patterns. The present study offers an expanded picture of miRNAs for castor bean and other members in the family Euphorbiaceae.

Characterization and comparative profiling of MicroRNAs in a sexual dimorphism insect, Eupolyphaga sinensis Walker

BACKGROUND

MicroRNAs are now recognized as key post-transcriptional regulators in animal ontogenesis and phenotypic diversity. Eupolyphaga sinensis Walker (Blattaria) is a sexually dimorphic insect, which is also an important source of material used in traditional Chinese medicine. The male E. sinensis have shorter lifecycles and go through fewer instars than the female. Furthermore, the males have forewings, while the females are totally wingless.

RESULTS

We used the Illumina/Solexa deep sequencing technology to sequence small RNA libraries prepared from the fourth-instar larvae of male and female E. sinensis. 19,097,799 raw reads were yielded in total: 7,817,445 reads from the female library and 11,280,354 from the male, respectively. As a result, we identified 168 known miRNAs belonging to 55 families as well as 204 novel miRNAs. Moreover, 45 miRNAs showed significantly different expression between the female and the male fourth-instar larvae, and we validated 10 of them by Stem-loop qRT-PCR. Some of these differentially expressed miRNAs are related to metamorphosis, development and phenotypic diversity.

CONCLUSIONS/SIGNIFICANCE

This is the first comprehensive description of miRNAs in E. sinensis. The results provide a useful resource for further in-depth study on molecular regulation and evolution of miRNAs. These findings not only enrich miRNAs for hemimetabolans but also lay the foundation for the study of post-transcriptional regulation on the phenomena of sexual dimorphism.

Comparison of Analysis Tools for miRNA High Throughput Sequencing Using Nerve Crush as a Model

Recent advances in sample preparation and analysis for next generation sequencing have made it possible to profile and discover new miRNAs in a high throughput manner. In the case of neurological disease and injury, these types of experiments have been more limited. Possibly because tissues such as the brain and spinal cord are inaccessible for direct sampling in living patients, and indirect sampling of blood and cerebrospinal fluid are affected by low amounts of RNA. We used a mouse model to examine changes in miRNA expression in response to acute nerve crush. We assayed miRNA from both muscle tissue and blood plasma. We examined how the depth of coverage (the number of mapped reads) changed the number of detectable miRNAs in each sample type. We also found that samples with very low starting amounts of RNA (mouse plasma) made high depth of mature miRNA coverage more difficult to obtain. Each tissue must be assessed independently for the depth of coverage required to adequately power detection of differential expression, weighed against the cost of sequencing that sample to the adequate depth. We explored the changes in total mapped reads and differential expression results generated by three different software packages: miRDeep2, miRNAKey, and miRExpress and two different analysis packages, DESeq and EdgeR. We also examine the accuracy of using miRDeep2 to predict novel miRNAs and subsequently detect them in the samples using qRT-PCR.

Identification and characterization of novel and conserved microRNAs in radish (Raphanus sativus L.) using high-throughput sequencing

MicroRNAs (miRNAs) are endogenous, non-coding, small RNAs that play significant regulatory roles in plant growth, development, and biotic and abiotic stress responses. To date, a great number of conserved and species-specific miRNAs have been identified in many important plant species such as Arabidopsis, rice and poplar. However, little is known about identification of miRNAs and their target genes in radish (Raphanus sativus L.). In the present study, a small RNA library from radish root was constructed and sequenced using the high-throughput Solexa sequencing. Through sequence alignment and secondary structure prediction, a total of 545 conserved miRNA families as well as 15 novel (with their miRNA* strand) and 64 potentially novel miRNAs were identified. Quantitative real-time PCR (qRT-PCR) analysis confirmed that both conserved and novel miRNAs were expressed in radish, and some of them were preferentially expressed in certain tissues. A total of 196 potential target genes were predicted for 42 novel radish miRNAs. Gene ontology (GO) analysis showed that most of the targets were involved in plant growth, development, metabolism and stress responses. This study represents a first large-scale identification and characterization of radish miRNAs and their potential target genes. These results could lead to the further identification of radish miRNAs and enhance our understanding of radish miRNA regulatory mechanisms in diverse biological and metabolic processes.

Identification and characterization of microRNAs expressed in human breast cancer T-47D cells in response to prolactin treatment by Solexa deep-sequencing technology

MicroRNAs (miRNAs) are key regulators of gene expression and perform critical roles in various biological processes. To investigate the functional roles of miRNAs in the prolactin receptor (PRLR) signaling pathway in breast cancer, we constructed two small RNA libraries from human breast cancer T-47D cells treated with or without prolactin (PRL). The miRNA expression profiles were systematically screened using Solexa deep-sequencing technology. More than 40 miRNAs were significantly differentially expressed, from which 4 miRNAs were chosen for validation by stem-loop real-time PCR. In addition, 3 novel miRNAs were selected for verification by PCR. Furthermore, upstream miRNA target genes were predicted using different algorithms, GO and KEGG analyses revealed that these targets were highly related to the PRLR signaling pathway. This study provides a reference for elucidating the complex miRNA-mediated regulatory networks of PRL/PRLR signaling pathway that affect breast cancer tumorigenesis and progression.