Identification of miRNAs and Their Target Genes in Peach (Prunus persica L.) Using High-Throughput Sequencing and Degradome Analysis

MicroRNAs play critical roles in various biological and metabolic processes. The function of miRNAs has been widely studied in model plants such as Arabidopsis and rice. However, the number of identified miRNAs and related miRNA targets in peach (Prunus persica) is limited. To understand further the relationship between miRNAs and their target genes during tissue development in peach, a small RNA library and three degradome libraries were constructed from three tissues for deep sequencing. We identified 117 conserved miRNAs and 186 novel miRNA candidates in peach by deep sequencing and 19 conserved miRNAs and 13 novel miRNAs were further evaluated for their expression by RT-qPCR. The number of gene targets that were identified for 26 conserved miRNA families and 38 novel miRNA candidates, were 172 and 87, respectively. Some of the identified miRNA targets were abundantly represented as conserved miRNA targets in plant. However, some of them were first identified and showed important roles in peach development. Our study provides information concerning the regulatory network of miRNAs in peach and advances our understanding of miRNA functions during tissue development.     

Identification and expression analysis of miRNAs in germination and seedling growth of Tibetan hulless barley

Germination and seedling growth are crucial for plant development and agricultural production. While, the regulatory mechanisms during these processes in Tibetan hulless barley (Hordeum vulgare L. var. nudum) are not well understood. Given the regulatory roles of microRNAs (miRNAs) in crop plants and the irreplaceability of barley in the highland area of China, we herein presented a genome-wide survey of miRNAs to reveal a potential regulatory network in the early developmental stages of two Tibetan hulless barleys, from which a total of 156 miRNAs was identified including 35 known and 121 novel ones. Six of the identified novel miRNAs were further experimentally validated. According to the evolutionary analysis, miR156, miR166, miR168, and miR171 were conserved across Tibetan hulless barleys and eight other seed plants. Expression profiles of ten known miRNAs showed that they were involved in phytohormone signaling, carbohydrate and lipid metabolism, as well as juvenile-adult transition during barley development. Moreover, a total of 1280 genes targeted by 101 miRNAs were predicted from both barley libraries. Three genes (PLN03212, MATE eukaryotic, and GRAS) were validated via the RNA ligase-mediated 5′-rapid amplification of cDNA ends (RLM-5' RACE) to be the targets of hvu-miR159a, hvu-miR166a, and hvu-miR171-3p, respectively. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of putative targets, the most abundant pathways were related to “metabolism”.These results revealed that miRNA-target pairs participating in the regulation of multigene expression and the embryonic development of Tibetan hulless barleys were controlled by complex mechanisms involving the concordant expression of different miRNAs and feedback loops among miRNAs as well as their targets. The study provides insight into the regulatory network of barley miRNAs for better understanding of miRNA functions during germination and seedling growth.     

microRNAs in a multicellular green alga Volvox carteri

microRNAs(miRNAs)have emerged as key components in the eukaryotic gene regulatory network.We and others have previously identified many miRNAs in a unicellular green alga,Chlamydomonas reinhardtii.To investigate whether miRNA-mediated gene regulation is a general mechanism in green algae and how miRNAs have been evolved in the green algal lineage,we examined small RNAs in Volvox carteri,a multicellular species in the same family with Chlamydomonas reinhardtii.We identified 174 miRNAs in Volvox,with many of them being highly enriched in gonidia or somatic cells.The targets of the miRNAs were predicted and many of them were subjected to miRNA-mediated cleavage in vivo,suggesting that miRNAs play regulatory roles in the biology of green algae.Our catalog of miRNAs and their targets provides a resource for further studies on the evolution,biological functions,and genomic properties of miRNAs in green algae.     

Identification of Conserved and Novel MicroRNAs in the Pacific Oyster Crassostrea gigas by Deep Sequencing

MicroRNAs (miRNAs) play important roles in regulatory processes in various organisms. To date many studies have been performed in the investigation of miRNAs of numerous bilaterians, but limited numbers of miRNAs have been identified in the few species belonging to the clade Lophotrochozoa. In the current study, deep sequencing was conducted to identify the miRNAs of Crassostrea gigas (Lophotrochozoa) at a genomic scale, using 21 libraries that included different developmental stages and adult organs. A total of 100 hairpin precursor loci were predicted to encode miRNAs. Of these, 19 precursors (pre-miRNA) were novel in the oyster. As many as 53 (53%) miRNAs were distributed in clusters and 49 (49%) precursors were intragenic, which suggests two important biogenetic sources of miRNAs. Different developmental stages were characterized with specific miRNA expression patterns that highlighted regulatory variation along a temporal axis. Conserved miRNAs were expressed universally throughout different stages and organs, whereas novel miRNAs tended to be more specific and may be related to the determination of the novel body plan. Furthermore, we developed an index named the miRNA profile age index (miRPAI) to integrate the evolutionary age and expression levels of miRNAs during a particular developmental stage. We found that the swimming stages were characterized by the youngest miRPAIs. Indeed, the large-scale expression of novel miRNAs indicated the importance of these stages during development, particularly from organogenetic and evolutionary perspectives. Some potentially important miRNAs were identified for further study through significant changes between expression patterns in different developmental events, such as metamorphosis. This study broadened the knowledge of miRNAs in animals and indicated the presence of sophisticated miRNA regulatory networks related to the biological processes in lophotrochozoans.     

Comparative Analysis Reveals Dynamic Changes in miRNAs and Their Targets and Expression during Somatic Embryogenesis in Longan (Dimocarpus longan Lour.)

Somatic embryogenesis (SE), which resembles zygotic embryogenesis, is an essential component of the process of plant cell differentiation and embryo development. Although microRNAs (miRNAs) are important regulators of many plant develop- mental processes, their roles in SE have not been thoroughly investigated. In this study, we used deep-sequencing, computational, and qPCR methods to identify, profile, and describe conserved and novel miRNAs involved in longan (Dimocarpus longan) SE. A total of 643 conserved and 29 novel miRNAs (including star strands) from more than 169 miRNA families were identified in longan embryogenic tissue using Solexa sequencing. By combining computational and degradome sequencing approaches, we were able to predict 2063 targets of 272 miRNAs and verify 862 targets of 181 miRNAs. Target annotation revealed that the putative targets were involved in a broad variety of biological processes, including plant metabolism, signal transduction, and stimulus response. Analysis of stage- and tissue-specific expressions of 20 conserved and 4 novel miRNAs indicated their possible roles in longan SE. These miRNAs were dlo-miR156 family members and dlo-miR166c* associated with early embryonic culture developmental stages; dlo-miR26, dlo-miR160a, and families dlo-miR159, dlo-miR390, and dlo-miR398b related to heart-shaped and torpedo- shaped embryo formation; dlo-miR4a, dlo-miR24, dlo-miR167a, dlo-miR168a*, dlo-miR397a, dlo-miR398b.1, dlo-miR398b.2, dlo-miR808 and dlo-miR5077 involved in cotyledonary embryonic development; and dlo-miR17 and dlo-miR2089*-1 that have regulatory roles during longan SE. In addition, dlo-miR167a, dlo-miR808, and dlo-miR5077 may be required for mature embryo formation. This study is the first reported investigation of longan SE involving large-scale cloning, characterization, and expression profiling of miRNAs and their targets. The reported results contribute to our knowledge of somatic embryo miRNAs and provide insights into miRNA biogenesis and expression in plant somatic embryo development.     

An oligonucleotide microarray for microRNA expression analysis based on labeling RNA with quantum dot and nanogold probe

MicroRNAs (miRNAs) play important regulatory roles in animals and plants by targeting mRNAs for cleavage or translational repression. They have diverse expression patterns and might regulate various developmental and physiological processes. Profiling miRNA expression is very helpful for studying biological functions of miRNAs. We report a novel miRNA profiling microarray, in which miRNAs were directly labeled at the 3′ terminus with biotin and hybridized with complementary oligo-DNA probes immobilized on glass slides, and subsequently detected by measuring fluorescence of quantum dots labeled with streptavidin bound to miRNAs through streptavidin–biotin interaction. The detection limit of this microarray for miRNA was ~0.4 fmol, and the detection dynamic range spanned about 2 orders of magnitude. We made a model microarray to profile 11 miRNAs from leaf and root of rice (Oryza sativa L. ssp. indica) seedlings. The analysis results of the miRNAs had a good reproducibility and were consistent with the northern blot result. To avoid using high-cost detection equipment, colorimetric detection, a method based on nanogold probe coupled with silver enhancement, was also successfully introduced into miRNA profiling microarray detection.