Small RNA Transcriptome of Hibiscus Syriacus Provides Insights into the Potential Influence of microRNAs in Flower Development and Terpene Synthesis

MicroRNA Expression Profiles in Response to Phytophthora infestans and Oidium neolycopersici and Functional Identification of sly-miR397 in Tomato

Late blight and powdery mildew are two widespread tomato diseases caused by Phytophthora infestans and Oidium neolycopersici, respectively, which reduce the quantity and quality of tomato. MicroRNAs (miRNAs) play critical roles in tomato resistance to various pathogens. Investigating the function of miRNAs is of great significance in controlling tomato diseases. To identify potential miRNAs involved in the interaction of tomato with P. infestans or O. neolycopersici, we analyzed the expression profiles of small RNAs in tomato leaves infected with these two pathogens using RNA-seq technology. A total of 330 and 288 miRNAs exhibited differences in expression levels after exposure to P. infestans and O. neolycopersici, respectively. One hundred and forty-six commonly differentially expressed (DE) miRNAs responsive to P. infestans and O. neolycopersici infestation were detected, including 10 commonly known conserved DE miRNAs and 136 novel miRNAs. Among these known DE miRNAs, sly-miR397 was strongly downregulated in response to P. infestans or O. neolycopersici infection. Silencing of sly-miR397 resulted in enhanced tolerance to the pathogens, whereas overexpression of sly-miR397 showed increased susceptibility. Furthermore, changes in sly-miR397 expression could also affect expression levels of pathogenesis-related genes and reactive oxygen species-scavenging genes, leading to altered necrotic cells and H₂O₂ levels. In addition, the number of lateral branches significantly changed in transgenic plants. Taken together, our results provide potential miRNA resources for further research of miRNA-disease associations and indicates that sly-miR397 acts as a negative regulator of disease resistance and influences lateral branch development in tomato.

MicroRNAs in Woody Plants

MicroRNAs (miRNAs) are small (∼21-nucleotides) non-coding RNAs found in plant and animals. MiRNAs function as critical post-transcriptional regulators of gene expression by binding to complementary sequences in their target mRNAs, leading to mRNA destabilization and translational inhibition. Plant miRNAs have some distinct characteristics compared to their animal counterparts, including greater evolutionary conservation and unique miRNA processing methods. The lifecycle of a plant begins with embryogenesis and progresses through seed germination, vegetative growth, reproductive growth, flowering and fruiting, and finally senescence and death. MiRNAs participate in the transformation of plant growth and development and directly monitor progression of these processes and the expression of certain morphological characteristics by regulating transcription factor genes involved in cell growth and differentiation. In woody plants, a large and rapidly increasing number of miRNAs have been identified, but their biological functions are largely unknown. In this review, we summarize the progress of miRNA research in woody plants to date. In particular, we discuss the potential roles of these miRNAs in growth, development, and biotic and abiotic stresses responses in woody plants.

Comparative profile analysis reveals differentially expressed microRNAs regulate anther and pollen development in kenaf cytoplasmic male sterility line

Cytoplasmic male sterility (CMS) is advantageous in extensive crop breeding and represents a perfect model for understanding anther and pollen development research. MicroRNAs (miRNAs) play key roles in regulating various biological processes. However, the miRNA-mediated regulatory network in kenaf CMS occurrence remains largely unknown. In the present study, a comparative deep sequencing approach was used to investigate the miRNAs and their roles in regulating anther and pollen development during CMS occurrence. We identified 283 known and 46 new candidate miRNAs in kenaf anther. A total of 67 differentially expressed miRNAs (DEMs) were discovered between CMS and its maintainer line. Among them, 40 and 27 miRNAs were up- and downregulated, respectively. These 67 DEMs were predicted to target 189 genes. Validation of DEMs and putative target genes were confirmed by using real-time quantitative PCR. In addition, a potential miRNA-mediated regulatory network, which mainly involves the auxin signaling pathway, signal transduction, glycolysis and energy metabolism, gene expression, transmembrane transport, protein modification and metabolism, and floral development, that mediates anther development during CMS occurrence was proposed. Taken together, our findings provide a better understanding of the molecular mechanism of miRNA regulation in pollen development and CMS occurrence in kenaf.

Transcriptomic analyses of rice (Oryza sativa) genes and non-coding RNAs under nitrogen starvation using multiple omics technologies

BACKGROUND

Nitrogen (N) is a key macronutrient essential for plant growth, and its availability has a strong influence on crop development. The application of synthetic N fertilizers on crops has increased substantially in recent decades; however, the applied N is not fully utilized due to the low N use efficiency of crops. To overcome this limitation, it is important to understand the genome-wide responses and functions of key genes and potential regulatory factors in N metabolism.

RESULTS

Here, we characterized changes in the rice (Oryza sativa) transcriptome, including genes, newly identified putative long non-coding RNAs (lncRNAs), and microRNAs (miRNAs) and their target mRNAs in response to N starvation using four different transcriptome approaches. Analysis of rice genes involved in N metabolism and/or transport using strand-specific RNA-Seq identified 2588 novel putative lncRNA encoding loci. Analysis of previously published RNA-Seq datasets revealed a group of N starvation-responsive lncRNAs showing differential expression under other abiotic stress conditions. Poly A-primed sequencing (2P-Seq) revealed alternatively polyadenylated isoforms of N starvation-responsive lncRNAs and provided precise 3' end information on the transcript models of these lncRNAs. Analysis of small RNA-Seq data identified N starvation-responsive miRNAs and down-regulation of miR169 family members, causing de-repression of NF-YA, as confirmed by strand-specific RNA-Seq and qRT-PCR. Moreover, we profiled the N starvation-responsive down-regulation of root-specific miRNA, osa-miR444a.4-3p, and Degradome sequencing confirmed MADS25 as a novel target gene.

CONCLUSIONS

In this study, we used a combination of multiple RNA-Seq analyses to extensively profile the expression of genes, newly identified lncRNAs, and microRNAs in N-starved rice roots and shoots. Data generated in this study provide an in-depth understanding of the regulatory pathways modulated by N starvation-responsive miRNAs. The results of comprehensive, large-scale data analysis provide valuable information on multiple aspects of the rice transcriptome, which may be useful in understanding the responses of rice plants to changes in the N supply status of soil.