MicroRNAS and their regulatory roles in plants

Identification and expression profiling of microRNAs involved in the stigma exsertion under high-temperature stress in tomato

Background

Autogamy in cultivated tomato varieties is a derived trait from wild type tomato plants, which are mostly allogamous. However, environmental stresses can cause morphological defects in tomato flowers and hinder autogamy. Under elevated temperatures, tomato plants usually exhibit the phenotype of stigma exsertion, with severely hindered self-pollination and fruit setting, whereas the inherent mechanism of stigma exsertion have been hitherto unknown. Numerous small RNAs (sRNAs) have been shown to play significant roles in plant development and stress responses, however, none of them have been studied with respect to stamen and pistil development under high-temperature conditions. We investigated the associations between stigma exsertion and small RNAs using high-throughput sequencing technology and molecular biology approaches.

Results

Sixteen sRNA libraries of Micro-Tom were constructed from plants stamen and pistil samples and sequenced after 2 d and 12 d of exposure to heat stress, respectively, from which a total of 110 known and 84 novel miRNAs were identified. Under heat stress conditions, 34 known and 35 novel miRNAs were differentially expressed in stamens, and 20 known and 10 novel miRNAs were differentially expressed in pistils. GO and KEGG pathway analysis showed that the predicted target genes of differentially expressed miRNAs were significantly enriched in metabolic pathways in both stamen and pistil libraries. Potential miRNA-target cleavage cascades that correlated with the regulation of stigma exsertion under heat stress conditions were found and validated through qRT-PCR and RLM-5′ RACE.

Conclusion

Overall, a global spectrum of known and novel miRNAs involved in tomato stigma exsertion and induced by high temperatures were identified using high-throughput sequencing and molecular biology approaches, laying a foundation for revealing the miRNA-mediated regulatory network involved in the development of tomato stamens and pistils under high-temperature conditions.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4238-9) contains supplementary material, which is available to authorized users.

Identification and expression analysis of microRNAs during ovule development in rice (Oryza sativa) by deep sequencing

MicroRNA (miRNA) expression profiles during rice ovule development revealed the possible miRNA-mediated regulation between ovule sporophytic tissue and female gametophyte and the involvement of miRNAs in programmed cell death. MiRNAs are 20-24-nucleotide small RNAs that play key roles in the regulation of many growth and developmental processes in plants. Rice ovule development comprises a series of biological events, which are regulated by complex molecular mechanisms. To gain insight into miRNA-mediated regulation of rice ovule development, Illumina sequencing was used to examine the expression of miRNAs from the megaspore mother cell meiosis stage to the fertilized ovule stage. Based on the sequencing data, 486 known and 204 novel miRNAs were identified during rice ovule development. Moreover, 56, 65 and 11 differentially expressed miRNAs between adjacent developmental stages were identified. By analyzing transcriptome and degradome data, we identified 41, 65 and 12 coherent target genes for the differentially expressed miRNAs in ovule development. We found that changes in the expression of plant hormone-related miRNAs may play important roles in embryo sac development, providing evidence for cross-talk communication between sporophytic tissue and the female gametophyte. Additionally, we revealed that miRNAs may be involved in programmed cell death after fertilization. Finally, we constructed miRNA-mediated regulatory networks that are active during rice ovule development.

miR398 and miR395 are involved in response to SO2 stress in Arabidopsis thaliana

Sulfur dioxide (SO₂) is a common air pollutant that has adverse effects on plants. MicroRNAs (miRNAs) are small noncoding RNA that play critical roles in plant development and stress response. In this study, we found that two miRNAs, miR398 and miR395, were differentially expressed in Arabidopsis shoots under SO₂ stress. The expression of miR398 was down-regulated, and the transcript levels of its target genes, Cu/Zn superoxide dismutases (CSD1 and CSD2), were increased during SO₂ exposure. The activity of superoxide dismutase (SOD), one of the major antioxidant enzymes, was enhanced with the increase in the CSD transcript level, suggesting an important role of miR398 in response to SO₂-induced oxidative stress. Meanwhile, the expression of miR395 was increased, and the transcript levels of its target genes, ATP sulfurylases (APS3 and APS4) and a low-affinity sulfate transporter (SULTR2;1), were decreased in Arabidopsis shoots, showing that miR395 played important roles in the regulation of sulfate assimilation and translocation during SO₂ exposure. The content of glutathione (GSH), an important sulfur-containing antioxidant, was enhanced with the changes in sulfur metabolism in Arabidopsis shoots under SO₂ stress. These results showed that both miR398 and miR395 were involved in protecting plants from oxidative damage during SO₂ exposure. Many stress-responsive cis-elements were found in the promoter regions of MIR398 and MIR395, suggesting that these miRNAs might respond to various environmental conditions, including SO₂ stress. Overall, our study provides an insight into the regulatory roles of miRNAs in response to SO₂ stress in plants, and highlights the molecular mechanisms of plant adaptation to environmental stress.

miR156 switches on vegetative phase change under the regulation of redox signals in apple seedlings

In higher plants, miR156 regulates the vegetative phase change via the target SBP/SPL genes. The regulation of miR156 during ontogenetic processes is not fully understood. In the apple genome, of 31 putative MdMIR156 genes that encode pre-miR156, seven were dominantly expressed. However, the transcript levels of only MdMIR156a5 and MdMIR156a12 decreased significantly during the vegetative phase change, which was consistent with the mature miR156 level, indicating that miR156 is under transcriptional regulation. Leaf H₂O₂ content was higher in the adult phase than in the juvenile phase because of excess H₂O₂ accumulation in chloroplasts. When in vitro shoots were treated with menadione, diphenyleneiodonium, L-2-oxothiazolidine-4-carboxylic acid or buthionine sulphoximine, the expressions of MdMIR156a5, MdMIR156a12, and as well miR156 were coordinated with reduced glutathione (GSH) contents and glutathione/glutathione disulfide ratio but not H₂O₂ contents. Alteration of miR156 expression level by MdMIR156a6-overexpressing or miR156-mimetic transgenic Nicotiana benthamiana did not cause a corresponding change in reactive oxygen species or GSH status. Collectively, the results indicate that the vegetative phase change in apple is controlled by the MdMIR156a5 and MdMIR156a12 transcriptional regulatory network in response to the plastid–nucleus redox signals, such as GSH.

FASTmiR: an RNA-based sensor for in vitro quantification and live-cell localization of small RNAs

Small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs), play a variety of important regulatory roles in many eukaryotes. Their small size has made it challenging to study them directly in live cells. Here we describe an RNA-based fluorescent sensor for small RNA detection both in vitro and in vivo, adaptable for any small RNA. It utilizes an sxRNA switch for detection of miRNA–mRNA interactions combined with a fluorophore-binding sequence ‘Spinach’, a GFP-like RNA aptamer for which the RNA–fluorophore complex exhibits strong and consistent fluorescence under an excitation wavelength. Two example sensors, FASTmiR171 and FASTmiR122, can rapidly detect and quantify the levels of miR171 and miR122 in vitro. The sensors can determine relative levels of miRNAs in total RNA extracts with sensitivity similar to small RNA sequencing and northern blots. FASTmiR sensors were also used to estimate the copy number range of miRNAs in total RNA extracts. To localize and analyze the spatial distribution of small RNAs in live, single cells, tandem copies of FASTmiR122 were expressed in different cell lines. FASTmiR122 was able to quantitatively detect the differences in miR122 levels in Huh7 and HEK293T cells demonstrating its potential for tracking miRNA expression and localization in vivo.

Identification of functionally important microRNAs from rice inflorescence at heading stage of a qDTY4.1-QTL bearing Near Isogenic Line under drought conditions

A cross between IR64 (high-yielding but drought-susceptible) and Aday Sel (drought-tolerant) rice cultivars yielded a stable line with enhanced grain yield under drought screening field trials at International Rice Research Institute. The major effect qDTY4.1 drought tolerance and yield QTL was detected in the IR77298-14-1-2-10 Backcrossed Inbred Line (BIL) and its IR87705-7-15-B Near Isogenic Line (NIL) with 93.9% genetic similarity to IR64. Although rice yield is extremely susceptible to water stress at reproductive stage, currently, there is only one report on the detection of drought-responsive microRNAs in inflorescence tissue of a Japonica rice line. In this study, more drought-responsive microRNAs were identified in the inflorescence tissues of IR64, IR77298-14-1-2-10 and IR87705-7-15-B via next-generation sequencing. Among the 32 families of inflorescence-specific non-conserved microRNAs that were identified, 22 families were up-regulated in IR87705-7-15-B. Overall 9 conserved and 34 non-conserved microRNA families were found as drought-responsive in rice inflorescence with 5 conserved and 30 non-conserved families induced in the IR87705-7-15-B. The observation of more drought-responsive non-conserved microRNAs may imply their prominence over conserved microRNAs in drought response mechanisms of rice inflorescence. Gene Ontology annotation analysis on the target genes of drought-responsive microRNAs identified in IR87705-7-15-B revealed over-representation of biological processes including development, signalling and response to stimulus. Particularly, four inflorescence-specific microRNAs viz. osa-miR5485, osa-miR5487, osa-miR5492 and osa-miR5517, and two non-inflorescence specific microRNAs viz. osa-miR169d and osa-miR169f.2 target genes that are involved in flower or embryonic development. Among them, osa-miR169d, osa-miR5492 and osa-miR5517 are related to flowering time control. It is also worth mentioning that osa-miR2118 and osa-miR2275, which are implicated in the biosynthesis of rice inflorescence-specific small interfering RNAs, were induced in IR87705-7-15-B but repressed in IR77298-14-1-2-10. Further, gene search within qDTY4.1 QTL region had identified multiple copies of NBS-LRR resistance genes (potential target of osa-miR2118), subtilisins and genes implicated in stomatal movement, ABA metabolism and cuticular wax biosynthesis.

Integrating transcriptome and microRNA analysis identifies genes and microRNAs for AHO-induced systemic acquired resistance in N. tabacum

3-Acetonyl-3-hydroxyoxindole (AHO) induces systemic acquired resistance (SAR) in Nicotiana. However, the underlying molecular mechanism is not well understood. To understand the molecular regulation during SAR induction, we examined mRNA levels, microRNA (miRNA) expression, and their regulatory mechanisms in control and AHO-treated tobacco leaves. Using RNA-seq analysis, we identified 1,445 significantly differentially expressed genes (DEGs) at least 2 folds with AHO treatment. The DEGs significantly enriched in six metabolism pathways including phenylpropanoid biosynthesis, sesquiterpenoid and triterpenoid biosynthesis for protective cuticle and wax. Key DEGs including PALs and PR-10 in salicylic acid pathway involved in SAR were significantly regulated. In addition, we identified 403 miRNAs belonging to 200 miRNA families by miRNA sequencing. In total, AHO treatment led to 17 up- and 6 down-regulated at least 2 folds (Wald test, P < 0.05) miRNAs (DEMs), respectively. Targeting analysis implicated four DEMs regulating three DEGs involved in disease resistance, including miR156, miR172f, miR172g, miR408a, SPL6 and AP2. We concluded that both mRNA and miRNA regulation enhances AHO-induced SAR. These data regarding DEGs, miRNAs, and their regulatory mechanisms provide molecular evidence for the mechanisms involved in tobacco SAR, which are likely to be present in other plants.

Regulation of adrenal and ovarian steroidogenesis by miR-132

miR-132 is hormonally regulated in steroidogenic cells of the adrenal gland, ovary and testis. Here, we examined the potential role of miR-132 in the control of steroidogenesis. Transfection of Y1 adrenal cells with miR-132 increased mRNAs of 3β-HSD and 20α-HSD enzymes, which catalyze the sequential conversion of pregnenolone to progesterone to biologically inactive 20α-hydroxyprogesterone (20α-OHP). Overexpression of miR-132 reduced MeCP2 and StAR protein expression, basal progestin (progesterone and 20α-OHP) production, but enhanced their production in response to cAMP stimulation. Use of [³H] pregnenolone and free-diffusible 22(R)-hydroxycholesterol further confirmed that miR-132 promotes the production of 20α-OHP by upregulating 3β-HSD and 20α-HSD. Evidence is also presented that StAR is a direct target of miR-132. Transient transfection of Y1 cells with miR-132 demonstrated that miR-132 induction of 3β-HSD and 20α-HSD was accompanied by significant suppression of one of its target gene products, MeCP2. In contrast, co-expression of miR-132 plus MeCP2 protein partially blocked the ability of miR-132 to upregulate the expression and function of 3β-HSD and 20α-HSD. Moreover, suppression of MeCP2 protein with siRNA resulted in increased expression of 3β-HSD and 20α-HSD, further demonstrating that miR-132 induces the expression of these two enzymes via inhibition of MeCP2. Likewise, overexpression of miR-132 increased 20α-OHP production with and without HDL loading, while knockdown of miR-132 resulted in a significant decrease of 20α-OHP production by granulosa cells. In conclusion, our data suggest that miR-132 attenuates steroidogenesis by repressing StAR expression and inducing 20α-HSD via inhibition of MeCP2 to generate a biologically inactive 20α-OHP.

microRNA159-targeted SlGAMYB transcription factors are required for fruit set in tomato

The transition from flowering to fruit production, namely fruit set, is crucial to ensure successful sexual plant reproduction. Although studies have described the importance of hormones (i.e. auxin and gibberellins) in controlling fruit set after pollination and fertilization, the role of microRNA-based regulation during ovary development and fruit set is still poorly understood. Here we show that the microRNA159/GAMYB1 and -2 pathway (the miR159/GAMYB1/2 module) is crucial for tomato ovule development and fruit set. MiR159 and SlGAMYBs were expressed in preanthesis ovaries, mainly in meristematic tissues, including developing ovules. SlMIR159-overexpressing tomato cv. Micro-Tom plants exhibited precocious fruit initiation and obligatory parthenocarpy, without modifying fruit shape. Histological analysis showed abnormal ovule development in such plants, which led to the formation of seedless fruits. SlGAMYB1/2 silencing in SlMIR159-overexpressing plants resulted in misregulation of pathways associated with ovule and female gametophyte development and auxin signalling, including AINTEGUMENTA-like genes and the miR167/SlARF8a module. Similarly to SlMIR159-overexpressing plants, SlGAMYB1 was downregulated in ovaries of parthenocarpic mutants with altered responses to gibberellins and auxin. SlGAMYBs likely contribute to fruit initiation by modulating auxin and gibberellin responses, rather than their levels, during ovule and ovary development. Altogether, our results unveil a novel function for the miR159-targeted SlGAMYBs in regulating an agronomically important trait, namely fruit set.

Bypassing miRNA-mediated gene regulation under drought stress: alternative splicing affects CSD1 gene expression

The binding site for miR398 in an isoform of Cu/Zn superoxide dismutase (CSD1) is eliminated by alternative splicing to bypass miR398-mediated gene down-regulation under drought stress. MicroRNA (miRNA) binding sites (MBSs) are frequently interrupted by introns and therefore require proper splicing to generate functional MBSs in target transcripts. MBSs can also be excluded during splicing of pre-messenger RNA, leading to different regulation among isoforms. Previous studies have shown that levels of Cu/Zn superoxide dismutase (CSD) are down-regulated by miR398. In this study, sequences and transcript levels of peanut CSD1 isoforms (AhCSD1-1, AhCSD1-2.1, and AhCSD1-2.2) were analyzed under the drought stress. Results demonstrated that a miR398 binding site is eliminated in AhCSD1-2.2 as a consequence of alternative splicing, which bypasses miRNA-mediated down-regulation under drought stress. This alternative isoform was not only identified in peanut but also in soybean and Arabidopsis. In addition, transgenic Arabidopsis plants expressing AhCSD1 were more tolerant to osmotic stress. We hypothesize that the level of AhCSD1 is increased to allow diverse plant responses to overcome environmental challenges even in the presence of increased miR398 levels. These findings suggest that studies on the role of alternatively spliced MBSs affecting transcript levels are important for understanding plant stress responses.

ARGONAUTE10 Inhibits In Vitro Shoot Regeneration Via Repression of miR165/166 in Arabidopsis thaliana

Many plant cells retain their totipotency when cultured in vitro. The regulation of shoot regeneration from in vitro culture involves a number of gene products, but the nature of the associated post-transcriptional events remains largely unknown. Here, the post-transcriptional regulator ARGONAUTE10 (AGO10), a protein which is specifically expressed in the explant during the period when pro-shoot apical meristems (SAMs) are forming, has been known to inhibit shoot regeneration. In in vitro cultured explants of the loss-of-function mutant ago10, a much larger than normal number of SAMs was formed and, in these, the stem cell marker genes WUSCHEL, CLAVATA3 and SHOOT MERISTEMLESS were all strongly expressed. AGO10 repressed the accumulation of the microRNAs miR165/166, thereby up-regulating a suite of HD-ZIP III genes. The overproduction of miR166 was shown to promote shoot regeneration, while the absence of miR165/166 message resulted in a blockage to shoot regeneration and only a partial rescue of the phenotype of the ago10 mutant. The major conclusion was that the shoot regeneration inhibition determined by AGO10 functions via the repression of miR165/166.

Activation of secondary cell wall biosynthesis by miR319-targeted TCP4 transcription factor

The overexpression of miR319 in plants results in delayed senescence, and high levels of miR319-targeted TCP4 transcription factor cause premature onset of this process. However, the underlying mechanisms of this pathway remain elusive. Here, we found that miR319 overexpression results in a decrease in TCP4 abundance and secondary cell wall formation in the stem. Conversely, constitutive expression of miR319-resistant TCP4 promotes secondary cell wall formation, indicating that miR319-mediated TCP4 controls secondary cell wall formation during development. Further analysis revealed that TCP4 might directly bind the promoter of VND7 to activate its expression, which triggers the expression of a VND7 transcriptional network associated with secondary cell wall biosynthesis and programmed cell death and accelerates vessel formation. In addition, the development process gradually increased TCP4 expression. These results suggest that miR319 and its target TCP4 can act as switches that turn on secondary cell wall synthesis and programmed cell death.

microRNAs Make the Call in Cancer Personalized Medicine

Since their discovery and the advent of RNA interference, microRNAs have drawn enormous attention because of their ubiquitous involvement in cellular pathways from life to death, from metabolism to communication. It is also widely accepted that they possess an undeniable role in cancer both as tumor suppressors and tumor promoters modulating cell proliferation and migration, epithelial-mesenchymal transition and tumor cell invasion and metastasis. Moreover, microRNAs can even affect the tumor surrounding environment influencing angiogenesis and immune system activation and recruitment. The tight association of microRNAs with several cancer-related processes makes them undoubtedly connected to the effect of specific cancer drugs inducing either resistance or sensitization. In this context, personalized medicine through microRNAs arose recently with the discovery of single nucleotide polymorphisms in the target binding sites, in the sequence of the microRNA itself or in microRNA biogenesis related genes, increasing risk, susceptibility and progression of multiple types of cancer in different sets of the population. The depicted scenario implies that the overall variation displayed by these small non-coding RNAs have an impact on patient-specific pharmacokinetics and pharmacodynamics of cancer drugs, pushing on a rising need of personalized treatment. Indeed, microRNAs from either tissues or liquid biopsies are also extensively studied as valuable biomarkers for disease early recognition, progression and prognosis. Despite microRNAs being intensively studied in recent years, a comprehensive review describing these topics all in one is missing. Here we report an up-to-date and critical summary of microRNAs as tools for better understanding personalized cancer biogenesis, evolution, diagnosis and treatment.

tRNA-derived small RNAs target transposable element transcripts

tRNA-derived RNA fragments (tRFs) are 18–26 nucleotide small RNAs that are not random degradation products, but are rather specifically cleaved from mature tRNA transcripts. Abundant in stressed or viral-infected cells, the function and potential targets of tRFs are not known. We identified that in the unstressed wild-type male gamete containing pollen of flowering plants, and analogous reproductive structure in non-flowering plant species, tRFs accumulate to high levels. In the reference plant Arabidopsis thaliana, tRFs are processed by Dicer-like 1 and incorporated into Argonaute1 (AGO1), akin to a microRNA. We utilized the fact that many plant small RNAs direct cleavage of their target transcripts to demonstrate that the tRF–AGO1 complex acts to specifically target and cleave endogenous transposable element (TE) mRNAs produced from transcriptionally active TEs. The data presented here demonstrate that tRFs are bona-fide regulatory microRNA-like small RNAs involved in the regulation of genome stability through the targeting of TE transcripts.

Investigating the regulatory roles of the microRNAs and the Argonaute 1-enriched small RNAs in plant metabolism

The biological roles of small RNAs (sRNAs) in metabolic processes are emerging. However, a systemic study is needed to investigate the wide-spread involvement of the sRNAs in plant metabolism. By using the metabolism-related transcripts retrieved from the public database Plant Metabolic Network, and the publicly available sRNA high-throughput sequencing data, large-scale target identification was performed for microRNAs (miRNAs) and Argonaute 1 (AGO1)-enriched sRNAs in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa). Based on the publicly available degradome sequencing data, 200 miRNA/sRNA-target pairs involving 19 miRNAs, 111 AGO1-enriched sRNAs and 58 target transcripts in Arabidopsis, and 151 pairs involving 62 miRNAs, 33 AGO1-enriched sRNAs and 69 target transcripts in rice were identified. After considering protein-protein interactions for the above identified target genes, a total of 251 pairs involving 21 miRNAs, 120 AGO1-enriched sRNAs and 75 target transcripts exist within the regulatory network of Arabidopsis, and 168 pairs involving 64 miRNAs, 38 AGO1-enriched sRNAs and 80 target transcripts exist in rice. Based on GO (Gene Ontology) term enrichment analysis, the targets within the networks of both plants are enriched in "metabolic process" and "catalytic activity", pointing to the high relevance of the established networks to metabolism. Several functionally conserved subnetworks were identified between the two plant species. Our study provides a basis for studies on metabolism-related sRNAs in plants.

microRNAs participate in gene expression regulation and phytohormone cross-talk in barley embryo during seed development and germination

BACKGROUND

Small RNA and degradome sequencing have identified a large number of miRNA-target pairs in plant seeds. However, detailed spatial and temporal studies of miRNA-mediated regulation, which can reflect links between seed development and germination are still lacking.

RESULTS

In this study, we extended our investigation on miRNAs-involved gene regulation by a combined analysis of seed maturation and germination in barley. Through bioinformatics analysis of small RNA sequencing data, a total of 1324 known miRNA families and 448 novel miRNA candidates were identified. Of those, 16 known miRNAs with 40 target genes, and three novel miRNAs with four target genes were confirmed based on degradome sequencing data. Conserved miRNA families such as miR156, miR168, miR166, miR167, and miR894 were highly expressed in embryos of developing and germinating seeds. A barley-specific miRNA, miR5071, which was predicted to target an OsMLA10-like gene, accumulated at a high level, suggesting its involvement in defence response during these two developmental stages. Based on target prediction and Kyoto Encyclopedia of Genes and Genomes analysis of putative targets, nine highly expressed miRNAs were found to be related to phytohormone signalling and hormone cross-talk. Northern blot and qRT-PCR analysis showed that these miRNAs displayed differential expression patterns during seed development and germination, indicating their different roles in hormone signalling pathways. In addition, we showed that miR393 affected seed development through targeting two genes encoding the auxin receptors TIR1/AFBs in barley, as over-expression of miR393 led to an increased length-width ratio of seeds, whereas target mimic (MIM393)-mediated inhibition of its activity decreased the 1000-grain weight of seeds. Furthermore, the expression of auxin-responsive genes, abscisic acid- and gibberellic acid-related genes was altered in miR393 misexpression lines during germination and early seedling growth.

CONCLUSIONS

Our work indicates that miRNA-target pairs participate in gene expression regulation and hormone interaction in barley embryo and provides evidence that miR393-mediated auxin response regulation affects grain development and influences gibberellic acid and abscisic acid homeostasis during germination.

Bacillus subtilis affects miRNAs and flavanoids production in Agrobacterium-Tobacco interaction

Agrobacterium tumefaciens is a very destructive plant pathogen. Selection of effective biological agents against this pathogen depends on more insight into molecular plant defence responses during the biocontrol agent-pathogen interaction. Auxin as a phytohormone is a key contributor in pathogenesis and plant defence and accumulation of auxin transport carriers are accompanied by increasing in flavonoid and miRNAs concentrations during plant interactions with bacteria. The aim of this research was molecular analysis of Bacillus subtilis (ATCC21332) biocontrol effect against A. tumefaciens (IBRC-M10701) pathogen interacting with Nicotiana tabacum plants. Tobacco plants were either treated with both or one of the challenging bacteria and the expression of miRNAs inside the plants were analysed through qRT-PCR. The results indicated that the bacterial treatments affect expression level of nta-miRNAs. In tobacco plants treated only with A. tumefaciens the expression of nta-miR393 was more than that was recorded for nta-miR167 (3.8 folds, P < 0.05 in 3dpi). While the expression level of nta-miR167 was more than the expression of nta-miR393 in other treatments including tobacco plants treated only with B. subtilis (2.1 folds, P < 0.05) and the plants treated with both of the bacteria (3.9 folds, P < 0.05) in 3 dpi. Also, the composition and concentration of rutin, myrecetin, daidzein and vitexin flavanoid derivatives were detected using HPLC and analysed according the standard curves. All of the tested flavanoid compounds were highly detected in Tobacco plants which were only challenged with A. tumefaciens. The amount of these compounds in the plants which were challenged with the B. subtilis alone, was similar to the amount recorded for the plants challenged with the both bacteria. This study suggests a relationship between the upregulation of nta-miR167, nta-miR393 and accumulation of flavanoid compounds. Overall, the expression of these miRNAs as well as flavonoid derivatives has the potential of being used as biomarkers for the interaction of B. subtilis and A. tumefaciens model system in N. tabacum.

Malus hupehensis miR168 Targets to ARGONAUTE1 and Contributes to the Resistance against Botryosphaeria dothidea Infection by Altering Defense Responses

MicroRNA (miRNA)-mediated post-transcriptional regulation plays a fundamental role in various plant physiological processes, including responses to pathogens. MicroRNA168 has been implicated as an essential factor of miRNA pathways by targeting ARGONAUTE1 (AGO1), the core component of the RNA-induced silencing complex (RISC). A fluctuation in AGO1 expression influences various plant-pathogen interactions, and the homeostasis of AGO1 and miR168 accumulation is maintained by a complicated feedback regulatory loop. In this study, the connection between miR168 and the resistance of Malus hupehensis to Botryosphaeria dothidea is revealed. The induction of both the mature miR168 and its precursor in plants subjected to B. dothidea infection indicate the transcriptional activation of MIR168a. MIR168a promoter analysis demonstrates that the promoter can be activated by B. dothidea and salicylic acid (SA). However, the direct target of miR168, M. hupehensis ARGONAUTE1 (MhAGO1), is shown to be induced under the infection. Expression and transcription activity analysis demonstrate the transcriptional activation and the post-transcriptional suppression of MhAGO1 in response to B. dothidea infection. By inhibiting reactive oxygen species (ROS) production and enhancing SA-mediated defense responses, miR168a delays the symptom development of leaves inoculated with B. dothidea and impedes the pathogen growth, while MhAGO1 is found to have the opposite effects. Collectively, these findings suggest that the expression of miR168 and MhAGO1 in M. hupehensis in response to B. dothidea infection is regulated by a complicated mechanism. Targeting to MhAGO1, a negative regulator, miR168 plays a positive role in the resistance by alterations in diverse defense responses.

Small RNA profiles from Panax notoginseng roots differing in sizes reveal correlation between miR156 abundances and root biomass levels

Plant genomes encode several classes of small regulatory RNAs (sRNAs) that play critical roles in both development and stress responses. Panax notoginseng (Burk.) F.H. Chen (P. notoginseng) is an important traditional Chinese herbal medicinal plant species for its haemostatic effects. Therefore, the root yield of P. notoginseng is a major economically important trait since the roots of P. notoginseng are the parts used to produce medicine. To identify sRNAs that are critical for the root biomass of P. notoginseng, we performed a comprehensive study of miRNA transcriptomes from P. notoginseng roots of different biomasses. We identified 675 conserved miRNAs, of which 180 pre-miRNAs are also identified, and three TAS3 loci in P. notoginseng. By using degradome sequencing, we identified 79 conserved miRNA:target or tasiRNA:target interactions, of which eight were further confirmed with the RLM 5'-RACE experiments. More importantly, our results revealed that a member of miR156 family and one of its SPL target genes have inverse expression levels, which is tightly correlated with greater root biomass contents. These results not only contributes to overall understanding of post-transcriptional gene regulation in roots of P. notoginseng but also could serve as markers for breeding P. notoginseng with greater root yield.

On the performance of pre-microRNA detection algorithms

MicroRNAs are crucial for post-transcriptional gene regulation, and their dysregulation has been associated with diseases like cancer and, therefore, their analysis has become popular. The experimental discovery of miRNAs is cumbersome and, thus, many computational tools have been proposed. Here we assess 13 ab initio pre-miRNA detection approaches using all relevant, published, and novel data sets while judging algorithm performance based on ten intrinsic performance measures. We present an extensible framework, izMiR, which allows for the unbiased comparison of existing algorithms, adding new ones, and combining multiple approaches into ensemble methods. In an exhaustive attempt, we condense the results of millions of computations and show that no method is clearly superior; however, we provide a guideline for biomedical researchers to select a tool. Finally, we demonstrate that combining all of the methods into one ensemble approach, for the first time, allows reliable purely computational pre-miRNA detection in large eukaryotic genomes.As the experimental discovery of microRNAs (miRNAs) is cumbersome, computational tools have been developed for the prediction of pre-miRNAs. Here the authors develop a framework to assess the performance of existing and novel pre-miRNA prediction tools and provide guidelines for selecting an appropriate approach for a given data set.

miRCat2: accurate prediction of plant and animal microRNAs from next-generation sequencing datasets

MOTIVATION

MicroRNAs are a class of ∼21-22 nt small RNAs which are excised from a stable hairpin-like secondary structure. They have important gene regulatory functions and are involved in many pathways including developmental timing, organogenesis and development in eukaryotes. There are several computational tools for miRNA detection from next-generation sequencing datasets. However, many of these tools suffer from high false positive and false negative rates. Here we present a novel miRNA prediction algorithm, miRCat2. miRCat2 incorporates a new entropy-based approach to detect miRNA loci, which is designed to cope with the high sequencing depth of current next-generation sequencing datasets. It has a user-friendly interface and produces graphical representations of the hairpin structure and plots depicting the alignment of sequences on the secondary structure.

RESULTS

We test miRCat2 on a number of animal and plant datasets and present a comparative analysis with miRCat, miRDeep2, miRPlant and miReap. We also use mutants in the miRNA biogenesis pathway to evaluate the predictions of these tools. Results indicate that miRCat2 has an improved accuracy compared with other methods tested. Moreover, miRCat2 predicts several new miRNAs that are differentially expressed in wild-type versus mutants in the miRNA biogenesis pathway.

AVAILABILITY AND IMPLEMENTATION

miRCat2 is part of the UEA small RNA Workbench and is freely available from http://srna-workbench.cmp.uea.ac.uk/.

CONTACT

v.moulton@uea.ac.uk or s.moxon@uea.ac.uk.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Uncovering Male Fertility Transition Responsive miRNA in a Wheat Photo-Thermosensitive Genic Male Sterile Line by Deep Sequencing and Degradome Analysis

MicroRNAs (miRNAs) are endogenous small RNAs which play important negative regulatory roles at both the transcriptional and post-transcriptional levels in plants. Wheat is the most commonly cultivated plant species worldwide. In this study, RNA-seq analysis was used to examine the expression profiles of miRNA in the spikelets of photo-thermosenisitive genic male sterile (PTGMS) wheat line BS366 during male fertility transition. Through mapping on their corresponding precursors, 917-7,762 novel miRNAs were found in six libraries. Six novel miRNAs were selected for examination of their secondary structures and confirmation by stem-loop RT-PCR. In a differential expression analysis, 20, 22, and 58 known miRNAs exhibited significant differential expression between developmental stages 1 (secondary sporogenous cells had formed), 2 (all cells layers were present and mitosis had ceased), and 3 (meiotic division stage), respectively, of fertile and sterile plants. Some of these differential expressed miRNAs, such as tae-miR156, tae-miR164, tae-miR171, and tae-miR172, were shown to be associated with their targets. These targets were previously reported to be related to pollen development and/or male sterility, indicating that these miRNAs and their targets may be involved in the regulation of male fertility transition in the PTGMS wheat line BS366. Furthermore, target genes of miRNA cleavage sites were validated by degradome sequencing. In this study, a possible signal model for the miRNA-mediated signaling pathway during the process of male fertility transition in the PTGMS wheat line BS366 was developed. This study provides a new perspective for understanding the roles of miRNAs in male fertility in PTGMS lines of wheat.

Integrated miRNA and mRNA expression profiling reveals the response regulators of a susceptible tomato cultivar to early blight disease

Early blight, caused by the fungus Alternaria solani, is a devastating foliar disease of tomatoes, causes massive yield loss each year worldwide. Molecular basis of the compatible host–pathogen interaction was elusive. We adopted next generation sequencing approach to decipher miRNAs and mRNAs that are differentially expressed during Alternaria-stress in tomato. Some of the interesting findings were also validated by alternative techniques. Our analysis revealed 181 known-miRNAs, belonging to 121 miRNA families, of which 67 miRNAs showed at least 2-fold change in expression level with the majority being downregulated. Concomitantly, 5,450 mRNAs were significantly regulated in the same diseased tissues. Differentially expressed genes were most significantly associated with response to stimulus process, photosynthesis, biosynthesis of secondary metabolites, plant–pathogen interaction and plant hormone signal transduction pathways. GO term enrichment-based categorization of gene-functions further supported this observation, as terms related to pathogen perception, disease signal transduction, cellular metabolic processes including oxidoreductase and kinase activity were over represented. In addition, we have discovered 102 miRNA–mRNA pairs which were regulated antagonistically, and careful study of the targeted mRNAs depicted that multiple transcription factors, nucleotide-binding site leucine-rich repeats, receptor-like proteins and enzymes related to cellular ROS management were profoundly affected. These studies have identified key regulators of Alternaria-stress response in tomato and the subset of genes that are likely to be post-transcriptionally silenced during the infection.

Genome-wide identification of soybean microRNA responsive to soybean cyst nematodes infection by deep sequencing

BACKGROUND

The soybean cyst nematode (SCN), Heterodera glycines, is one of the most devastating diseases limiting soybean production worldwide. It is known that small RNAs, including microRNAs (miRNAs) and small interfering RNAs (siRNAs), play important roles in regulating plant growth and development, defense against pathogens, and responses to environmental changes.

RESULTS

In order to understand the role of soybean miRNAs during SCN infection, we analyzed 24 small RNA libraries including three biological replicates from two soybean cultivars (SCN susceptible KS4607, and SCN HG Type 7 resistant KS4313N) that were grown under SCN-infested and -noninfested soil at two different time points (SCN feeding establishment and egg production). In total, 537 known and 70 putative novel miRNAs in soybean were identified from a total of 0.3 billion reads (average about 13.5 million reads for each sample) with the programs of Bowtie and miRDeep2 mapper. Differential expression analyses were carried out using edgeR to identify miRNAs involved in the soybean-SCN interaction. Comparative analysis of miRNA profiling indicated a total of 60 miRNAs belonging to 25 families that might be specifically related to cultivar responses to SCN. Quantitative RT-PCR validated similar miRNA interaction patterns as sequencing results.

CONCLUSION

These findings suggest that miRNAs are likely to play key roles in soybean response to SCN. The present work could provide a framework for miRNA functional identification and the development of novel approaches for improving soybean SCN resistance in future studies.

Induction of cell death by tospoviral protein NSs and the motif critical for cell death does not control RNA silencing suppression activity

Groundnut bud necrosis virus induces necrotic symptoms in different hosts. Previous studies showed reactive oxygen species-mediated programmed cell death (PCD) resulted in necrotic symptoms. Transgenic expression of viral protein NSs mimics viral symptoms. Here, we showed a role for NSs in influencing oxidative burst in the cell, by analyzing H2O2 accumulation, activities of antioxidant enzymes and expression levels of vacuolar processing enzymes, H2O2-responsive microRNA 319a.2 plus its possible target metacaspase-8. The role of NSs in PCD, was shown using two NSs mutants: one in the Trp/GH3 motif (a homologue of pro-apototic domain) (NSsS189R) and the other in a non-Trp/GH3 motif (NSsL172R). Tobacco rattle virus (TRV) expressing NSsS189R enhanced the PCD response, but not TRV-NSsL172R, while RNA silencing suppression activity was lost in TRV-NSsL172R, but not in TRV-NSsS189R. Therefore, we propose dual roles of NSs in RNA silencing suppression and induction of cell death, controlled by different motifs.

Genome-wide identification of Hami melon miRNAs with putative roles during fruit development

MicroRNAs represent a family of small endogenous, non-coding RNAs that play critical regulatory roles in plant growth, development, and environmental stress responses. Hami melon is famous for its attractive flavor and excellent nutritional value, however, the mechanisms underlying the fruit development and ripening remains largely unknown. Here, we performed small RNA sequencing to investigate the roles of miRNAs during Hami melon fruit development. Two batches of flesh samples were collected at four fruit development stages. Small RNA sequencing yielded a total of 54,553,424 raw reads from eight libraries. 113 conserved miRNAs belonging to 30 miRNA families and nine novel miRNAs comprising nine miRNA families were identified. The expression of 42 conserved miRNAs and three Hami melon-specific miRNAs significantly changed during fruit development. Furthermore, 484 and 124 melon genes were predicted as putative targets of 29 conserved and nine Hami melon-specific miRNA families, respectively. GO enrichment analysis were performed on target genes, "transcription, DNA-dependent", "rRNA processing", "oxidation reduction", "signal transduction", "regulation of transcription, DNA-dependent", and "metabolic process" were the over-represented biological process terms. Cleavage sites of six target genes were validated using 5' RACE. Our results present a comprehensive set of identification and characterization of Hami melon fruit miRNAs and their potential targets, which provide valuable basis towards understanding the regulatory mechanisms in programmed process of normal Hami fruit development and ripening. Specific miRNAs could be selected for further research and applications in breeding practices.

Altered accumulation of osa-miR171b contributes to rice stripe virus infection by regulating disease symptoms

Viral infection affects the pattern of plant miRNA expression. It has been presumed that reduction of miR171 and several other miRNAs influences viral symptoms in plants. We here experimentally demonstrate the association of osa-miR171b with rice stripe virus (RSV) symptoms in rice. Inhibition of osa-miR171b caused stunting with reduced chlorophyll content in leaves similar to viral symptoms. Overexpression of osa-miR171b by an artificial miRNA extended vegetative growth and enhanced chlorophyll accumulation in leaves. Tillers were thicker, and panicles were longer with more spikelets in plants overexpressing osa-miR171b than in controls, but there were no differences in tiller numbers. Targets of osa-miR171b, OsSCL6-IIa, OsSCL6-IIb, and OsSCL6-IIc, were respectively up- and down-regulated in plants where osa-miR171b was inhibited or overexpressed. In plants overexpressing osa-miR171b, five positive regulators for heading development, Ehd1, Ehd2, Ehd3, Ehd4, and Hd3a were up-regulated, while the negative regulator Ghd7 was down-regulated. Plants overexpressing osa-miR171b were less susceptible to RSV and virus symptoms were attenuated. Taken together, the results reveal that a reduction of osa-miR171b in RSV-infected rice contributes to RSV symptoms, and provide more insight into the roles of osa-miR171b in rice.

Plant dehydrins: shedding light on structure and expression patterns of dehydrin gene family in barley

Dehydrins, an important group of late embryogenesis abundant proteins, accumulate in response to dehydration stresses and play protective roles under stress conditions. Herein, phylogenetic analysis of the dehydrin family was performed using the protein sequences of 108 dehydrins obtained from 14 plant species based on plant taxonomy and protein subclasses. Sub-cellular localization and phosphorylation sites of these proteins were also predicted. The protein features distinguishing these dehydrins categories were identified using various attribute weighting and decision tree analyses. The results revealed that the presence of the S motif preceding the K motif (Y_nSK_n, SK_n, and S_nKS) was more evident and the Y_nSK_n subclass was more frequent in monocots. In barley, as one of the most drought-tolerant crops, there are ten members of Y_nSK_n out of 13 HvDhns. In promoter regions, six types of abiotic stress-responsive elements were identified. Regulatory elements in UTR sequences of HvDhns were infrequent while only four miRNA targets were found. Furthermore, physiological parameters and gene expression levels of HvDhns were studied in tolerant (HV1) and susceptible (HV2) cultivars, and in an Iranian tolerant wild barley genotype (Spontaneum; HS) subjected to gradual water stress and after recovery duration at the vegetative stage. The results showed the significant impact of dehydration on dry matter, relative leaf water, chlorophyll contents, and oxidative damages in HV2 compared with the other studied genotypes, suggesting a poor dehydration tolerance, and incapability of recovering after re-watering in HV2. Under severe drought stress, among the 13 HvDhns genes, 5 and 10 were exclusively induced in HV1 and HS, respectively. The gene and protein structures and the expression patterns of HvDhns as well as the physiological data consistently support the role of dehydrins in survival and recovery of barley plants from drought particularly in HS. Overall, this information would be helpful for functional characterization of the Dhn family in plants.

Plant hormone signaling in flowering: An epigenetic point of view

Reproduction is one of the most important phases in an organism's lifecycle. In the case of angiosperm plants, flowering provides the major developmental transition from the vegetative to the reproductive stage, and requires genetic and epigenetic reprogramming to ensure the success of seed production. Flowering is regulated by a complex network of genes that integrate multiple environmental cues and endogenous signals so that flowering occurs at the right time; hormone regulation, signaling and homeostasis are very important in this process. Working alone or in combination, hormones are able to promote flowering by epigenetic regulation. Some plant hormones, such as gibberellins, jasmonic acid, abscisic acid and auxins, have important effects on chromatin compaction mediated by DNA methylation and histone posttranslational modifications, which hints at the role that epigenetic regulation may play in flowering through hormone action. miRNAs have been viewed as acting independently from DNA methylation and histone modification, ignoring their potential to interact with hormone signaling - including the signaling of auxins, gibberellins, ethylene, jasmonic acid, salicylic acid and others - to regulate flowering. Therefore, in this review we examine new findings about interactions between epigenetic mechanisms and key players in hormone signaling to coordinate flowering.

Overexpression of miR529a confers enhanced resistance to oxidative stress in rice (Oryza sativa L.)

Overexpressing miR529a can enhance oxidative stress resistance by targeting OsSPL2 and OsSPL14 genes that can regulate the expression of their downstream SOD and POD related genes. MicroRNAs are involved in the regulation of plant developmental and physiological processes, and their expression can be altered when plants suffered environment stresses, including salt, oxidative, drought and Cadmium. The expression of microRNA529 (miR529) can be induced under oxidative stress. However, its biological function under abiotic stress responses is still unclear. In this study, miR529a was overexpressed to investigate the function of miR529a under oxidative stress in rice. Our results demonstrated that the expression of miR529a can be induced by exogenous H₂O₂, and overexpressing miR529a can increase plant tolerance to high level of H₂O₂, resulting in increased seed germination rate, root tip cell viability, reduced leaf rolling rate and chlorophyll retention. The expression of oxidative stress responsive genes and the activities of superoxide dismutase (SOD) and peroxidase (POD) were increased in miR529a overexpression plant, which could help to reduce redundant reactive oxygen species (ROS). Furthermore, only OsSPL2 and OsSPL14 were targeted by miR529a in rice seedlings, repressing their expression in miR529aOE plants could lead to strengthen plant tolerance to oxidation stress. Our study provided the evidence that overexpression of miR529a could strengthen oxidation resistance, and its target genes OsSPL2 and OsSPL14 were responsible for oxidative tolerance, implied the manipulation of miR529a and its target genes regulation on H₂O₂ related response genes could improve oxidative stress tolerance in rice.

Puccinia striiformis f. sp. tritici microRNA-like RNA 1 (Pst-milR1), an important pathogenicity factor of Pst, impairs wheat resistance to Pst by suppressing the wheat pathogenesis-related 2 gene

Small RNAs (sRNAs), an important type of pathogenicity factor, contribute to impairing host immune responses. However, little is known about sRNAs in Puccinia striiformis f. sp. tritici (Pst), one of the most destructive pathogens of wheat (Triticum aestivum L.). Here, we report a novel microRNA-like RNA (milRNA) from Pst termed microRNA-like RNA 1 (Pst-milR1), which suppresses wheat defenses during wheat-Pst interactions. We identified Pst-milR1 as a novel milRNA in Pst. Biological prediction and co-transformation showed that Pst-milR1 takes part in cross-kingdom RNA interference (RNAi) events by binding the wheat pathogenesis-related 2 (PR2) gene. Silencing of the Pst-milR1 precursor resulted in increased wheat resistance to the virulent Pst isolate CYR31. PR2 knock-down plants increased the susceptibility of wheat to the avirulent Pst isolate CYR23. This suggests that Pst-milR1 represses the plant immune response by suppressing the expression of PR2. Taking our findings together, we postulate that Pst-milR1 is an important pathogenicity factor in Pst, which acts as an effector to suppress host immunity. Our results provide significant new insights into the pathogenicity of the stripe rust pathogen.

MicroRNAs and Their Regulatory Role in Sugarcane

Sugarcane, one of the most photosynthetically efficient crops, is an important source of sugar and feedstock for green energy and co-generation. The high level of polyploidy and genomic peculiarities in this crop point towards a complex mechanism of regulation for the economically important traits like sugar content, cane yield related traits, resistance to biotic and abiotic stresses etc. The regulatory pathways for these traits comprise of a number of genes, transcription factors and different categories of RNAs like small interference RNAs (siRNAs), and Micro RNAs (miRNAs). MicroRNAs (miRNAs) are found to play an important regulatory role in many crops. As in other crops, several miRNAs have been identified in sugarcane too and these are speculated to have a role in regulating the various metabolic processes. Role of miRNAs in relation to drought tolerance has been studied to a great extent in this crop. miRNAs have been predicted to be linked to expression of other traits like disease resistance, salinity tolerance, waterlogging and axillary bud growth in sugarcane. miRNAs can have a significant role in biomass production in sugarcane, as reported in several biofuel crops. Till now, miRNAs linked to sugar accumulation have not been identified in sugarcane, but studies suggest an important role for miRNAs in sugar metabolic pathway in crops like Sorghum and switch grass. It is presumed that in sugarcane too, sugar accumulation as well as the other important metabolic pathways might be regulated to some extent by the miRNAs. The review examines the progress made in understanding the miRNA regulation in sugarcane and the extent to which miRNA mediated regulation can be utilized in sugarcane improvement.

Major genes determining yield-related traits in wheat and barley

Current development of advanced biotechnology tools allows us to characterize the role of key genes in plant productivity. The implementation of this knowledge in breeding strategies might accelerate the progress in obtaining high-yielding cultivars. The achievements of the Green Revolution were based on a specific plant ideotype, determined by a single gene involved in gibberellin signaling or metabolism. Compared with the 1950s, an enormous increase in our knowledge about the biological basis of plant productivity has opened new avenues for novel breeding strategies. The large and complex genomes of diploid barley and hexaploid wheat represent a great challenge, but they also offer a large reservoir of genes that can be targeted for breeding. We summarize examples of productivity-related genes/mutants in wheat and barley, identified or characterized by means of modern biology. The genes are classified functionally into several groups, including the following: (1) transcription factors, regulating spike development, which mainly affect grain number; (2) genes involved in metabolism or signaling of growth regulators-cytokinins, gibberellins, and brassinosteroids-which control plant architecture and in consequence stem hardiness and grain yield; (3) genes determining cell division and proliferation mainly impacting grain size; (4) floral regulators influencing inflorescence architecture and in consequence seed number; and (5) genes involved in carbohydrate metabolism having an impact on plant architecture and grain yield. The implementation of selected genes in breeding programs is discussed, considering specific genotypes, agronomic and climate conditions, and taking into account that many of the genes are members of multigene families.

Evidence of Epigenetic Mechanisms Affecting Carotenoids

Epigenetic mechanisms are able to regulate plant development by generating non-Mendelian allelic interactions. An example of these are the responses to environmenal stimuli that result in phenotypic variability and transgression amongst important crop traits. The need to predict phenotypes from genotypes to understand the molecular basis of the genotype-by-environment interaction is a research priority. Today, with the recent discoveries in the field of epigenetics, this challenge goes beyond analyzing how DNA sequences change. Here we review examples of epigenetic regulation of genes involved in carotenoid synthesis and degradation, cases in which histone- and/or DNA-methylation, and RNA silencing at the posttranscriptional level affect carotenoids in plants.

In Silico Identification and Validation of Potential microRNAs in Kinnow Mandarin (Citrus reticulata Blanco)

MicroRNAs (miRNAs) are a large family of 19-25 nucleotides, regulatory, non-coding RNA molecules that control gene expression by cleaving or inhibiting the translation of target gene transcripts in animals and plants. Despite the important functions of miRNAs related to regulation of plant growth and development processes, metabolism, and abiotic and biotic stresses, little is known about the disease-related miRNA. Here, we present a new pipeline for miRNA analysis using expressed sequence tags (ESTs)-based bioinformatics approach in Kinnow mandarin, a commercially important citrus fruit crop. For this, 56,041 raw EST sequences of Citrus reticulata Blanco were retrieved from EST database in NCBI through step-by-step filtering and processing methods and 130 miRNAs were predicted. Upon blast with Citrus sinensis transcriptome data, these produced potential targets related to disease resistance proteins, pectin lyase-like superfamily proteins, lateral organ boundaries (LOB) domain-containing proteins 11, and protein phosphatase 2C family proteins, protein kinases, dehydrogenases, and methyltransferases. Majority of the predicted miRNAs were of 22, 23, and 24 nucleotides in length. To validate these computationally predicted miRNA, poly(A)-tailed Reverse Transcription-PCR was applied to detect the expression of seven miRNA which showed disease-related potential targets, in citrus greening diseased leaf tissues in comparison to the healthy tissues of Kinnow mandarin. Our study provides information on regulatory roles of these potential miRNAs for the citrus greening disease development, miRNA targets, and would be helpful for future research of miRNA function in citrus.

Identification and characterization of two RNA silencing suppressors encoded by ophioviruses

Citrus psorosis virus and Mirafiori lettuce big-vein virus are two members of the genus Ophiovirus, family Ophioviridae. So far, how these viruses can interfere in the antiviral RNA silencing pathway is not known. In this study, using a local GFP silencing assay on Nicotiana benthamiana, the 24K-25K and the movement protein (MP) of both viruses were identified as RNA silencing suppressor proteins. Upon their co-expression with GFP in N. benthamiana 16c plants, the proteins also showed to suppress systemic RNA (GFP) silencing. The MPCPsV and 24KCPsV proteins bind long (114 nucleotides) but not short-interfering (21 nt) dsRNA, and upon transgenic expression, plants showed developmental abnormalities that coincided with an altered miRNA accumulation pattern. Furthermore, both proteins were able to suppress miRNA-induced silencing of a GFP-sensor construct and the co-expression of MPCPsV and 24KCPsV exhibited a stronger effect, suggesting they act at different stages of the RNAi pathway.

Molecular regulation of sucrose catabolism and sugar transport for development, defence and phloem function

Sucrose (Suc) is the major end product of photosynthesis in mesophyll cells of most vascular plants. It is loaded into phloem of mature leaves for long-distance translocation to non-photosynthetic organs where it is unloaded for diverse uses. Clearly, Suc transport and metabolism is central to plant growth and development and the functionality of the entire vascular system. Despite vast information in the literature about the physiological roles of individual sugar metabolic enzymes and transporters, there is a lack of systematic evaluation about their molecular regulation from transcriptional to post-translational levels. Knowledge on this topic is essential for understanding and improving plant development, optimizing resource distribution and increasing crop productivity. We therefore focused our analyses on molecular control of key players in Suc metabolism and transport, including: (i) the identification of promoter elements responsive to sugars and hormones or targeted by transcription factors and microRNAs degrading transcripts of target genes; and (ii) modulation of enzyme and transporter activities through protein-protein interactions and other post-translational modifications. We have highlighted major remaining questions and discussed opportunities to exploit current understanding to gain new insights into molecular control of carbon partitioning for improving plant performance.

Abiotic stress miRNomes in the Triticeae

The continued growth in world population necessitates increases in both the quantity and quality of agricultural production. Triticeae members, particularly wheat and barley, make an important contribution to world food reserves by providing rich sources of carbohydrate and protein. These crops are grown over diverse production environments that are characterized by a range of environmental or abiotic stresses. Abiotic stresses such as drought, heat, salinity, or nutrient deficiencies and toxicities cause large yield losses resulting in economic and environmental damage. The negative effects of abiotic stresses have increased at an alarming rate in recent years and are predicted to further deteriorate due to climate change, land degradation, and declining water supply. New technologies have provided an important tool with great potential for improving crop tolerance to the abiotic stresses: microRNAs (miRNAs). miRNAs are small regulators of gene expression that act on many different molecular and biochemical processes such as development, environmental adaptation, and stress tolerance. miRNAs can act at both the transcriptional and post-transcriptional levels, although post-transcriptional regulation is the most common in plants where miRNAs can inhibit the translation of their mRNA targets via complementary binding and cleavage. To date, expression of several miRNA families such as miR156, miR159, and miR398 has been detected as responsive to environmental conditions to regulate stress-associated molecular mechanisms individually and/or together with their various miRNA partners. Manipulation of these miRNAs and their targets may pave the way to improve crop performance under several abiotic stresses. Here, we summarize the current status of our knowledge on abiotic stress-associated miRNAs in members of the Triticeae tribe, specifically in wheat and barley, and the miRNA-based regulatory mechanisms triggered by stress conditions. Exploration of further miRNA families together with their functions under stress will improve our knowledge and provide opportunities to enhance plant performance to help us meet global food demand.

GmDREB1 overexpression affects the expression of microRNAs in GM wheat seeds

MicroRNAs (miRNAs) are small regulators of gene expression that act on many different molecular and biochemical processes in eukaryotes. To date, miRNAs have not been considered in the current evaluation system for GM crops. In this study, small RNAs from the dry seeds of a GM wheat line overexpressing GmDREB1 and non-GM wheat cultivars were investigated using deep sequencing technology and bioinformatic approaches. As a result, 23 differentially expressed miRNAs in dry seeds were identified and confirmed between GM wheat and a non-GM acceptor. Notably, more differentially expressed tae-miRNAs between non-GM wheat varieties were found, indicating that the degree of variance between non-GM cultivars was considerably higher than that induced by the transgenic event. Most of the target genes of these differentially expressed miRNAs between GM wheat and a non-GM acceptor were associated with abiotic stress, in accordance with the product concept of GM wheat in improving drought and salt tolerance. Our data provided useful information and insights into the evaluation of miRNA expression in edible GM crops.

Systems biology and genome-wide approaches to unveil the molecular players involved in the pre-germinative metabolism: implications on seed technology traits

The pre-germinative metabolism is among the most fascinating aspects of seed biology. The early seed germination phase, or pre-germination, is characterized by rapid water uptake (imbibition), which directs a series of dynamic biochemical events. Among those are enzyme activation, DNA damage and repair, and use of reserve storage compounds, such as lipids, carbohydrates and proteins. Industrial seedling production and intensive agricultural production systems require seed stocks with high rate of synchronized germination and low dormancy. Consequently, seed dormancy, a quantitative trait related to the activation of the pre-germinative metabolism, is probably the most studied seed trait in model species and crops. Single omics, systems biology, QTLs and GWAS mapping approaches have unveiled a list of molecules and regulatory mechanisms acting at transcriptional, post-transcriptional and post-translational levels. Most of the identified candidate genes encode for regulatory proteins targeting ROS, phytohormone and primary metabolisms, corroborating the data obtained from simple molecular biology approaches. Emerging evidences show that epigenetic regulation plays a crucial role in the regulation of these mentioned processes, constituting a still unexploited strategy to modulate seed traits. The present review will provide an up-date of the current knowledge on seed pre-germinative metabolism, gathering the most relevant results from physiological, genetics, and omics studies conducted in model and crop plants. The effects exerted by the biotic and abiotic stresses and priming are also addressed. The possible implications derived from the modulation of pre-germinative metabolism will be discussed from the point of view of seed quality and technology.

MicroRNA156 improves drought stress tolerance in alfalfa (Medicago sativa) by silencing SPL13

Alfalfa (Medicago sativa) is an important forage crop that is often grown in areas that frequently experience drought and water shortage. MicroRNA156 (miR156) is an emerging tool for improving various traits in plants. We tested the role of miR156d in drought response of alfalfa, and observed a significant improvement in drought tolerance of miR156 overexpression (miR156OE) alfalfa genotypes compared to the wild type control (WT). In addition to higher survival and reduced water loss, miR156OE genotypes also maintained higher stomatal conductance compared to WT during drought stress. Furthermore, we observed an enhanced accumulation of compatible solute (proline) and increased levels of abscisic acid (ABA) and antioxidants in miR156OE genotypes. Similarly, alfalfa plants with reduced expression of miR156-targeted SPL13 showed reduced water loss and enhanced stomatal conductance, chlorophyll content and photosynthetic assimilation. Several genes known to be involved in drought tolerance were differentially expressed in leaf and root of miR156 overexpression plants. Taken together, our findings reveal that miR156 improves drought tolerance in alfalfa at least partially by silencing SPL13.

Genome-wide identification and characterization of miRNAome from tomato (Solanum lycopersicum) roots and root-knot nematode (Meloidogyne incognita) during susceptible interaction

Root-knot nematodes (RKNs, Meloidogyne spp.) are the most damaging plant parasites causing severe losses to crop production. The present study reports genome-wide identification and characterization of both tomato and RKN miRNAs simultaneously from RKN-infected susceptible tomato roots using high-throughput sequencing technique. RNAseq data from 11 small RNA libraries derived from 5 disease development stages identified 281 novel miRNAs of tomato in addition to 52 conserved and 4 variants of conserved miRNAs. Additionally, the same set of RNAseq data identified 38 conserved and 290 novel RKN miRNAs. Both tomato and RKN miRNAs showed differential expression at 5 stages of disease development based on digital expression profiles. In tomato, further validation through qRT-PCR confirmed that majority of miRNAs were significantly upregulated during susceptible response whereas downregulated during resistance response. The predicted targets of 8 conserved and 1 novel miRNAs were validated through 5’RLM-RACE. A negative correlation between expression profiles of a few conserved miRNAs (miR156, miR159, miR164 and miR396) and their targets (SBP, GAMYB-like, NAC and GRF1 transcription factor) was confirmed. A novel Sly_miRNA996 also showed a negative correlation with its target MYB-like transcription factor. These results indicate that the conserved and novel tomato miRNAs are involved in regulating developmental changes in host root during RKN infection. In RKN, the targets of conserved miRNAs were also predicted and a few of their predicted target genes are known to be involved in nematode parasitism. Further, the potential roles of both tomato and RKN miRNAs have been discussed.

MiR-9-5p promotes MSC migration by activating β-catenin signaling pathway

Mesenchymal stem cells (MSCs) have the potential to treat various tissue damages, but the very limited number of cells that migrate to the damaged region strongly restricts their therapeutic applications. Full understanding of mechanisms regulating MSC migration will help to improve their migration ability and therapeutic effects. Increasing evidence shows that microRNAs play important roles in the regulation of MSC migration. In the present study, we reported that miR-9-5p was upregulated in hepatocyte growth factor -treated MSCs and in MSCs with high migration ability. Overexpression of miR-9-5p promoted MSC migration, whereas inhibition of endogenous miR-9-5p decreased MSC migration. To elucidate the underlying mechanism, we screened the target genes of miR-9-5p and report for the first time that CK1α and GSK3β, two inhibitors of β-catenin signaling pathway, were direct targets of miR-9-5p in MSCs and that overexpression of miR-9-5p upregulated β-catenin signaling pathway. In line with these data, inhibition of β-catenin signaling pathway by FH535 decreased the miR-9-5p-promoted migration of MSCs, while activation of β-catenin signaling pathway by LiCl rescued the impaired migration of MSCs triggered by miR-9-5p inhibitor. Furthermore, the formation and distribution of focal adhesions as well as the reorganization of F-actin were affected by the expression of miR-9-5p. Collectively, these results demonstrate that miR-9-5p promotes MSC migration by upregulating β-catenin signaling pathway, shedding light on the optimization of MSCs for cell replacement therapy through manipulating the expression level of miR-9-5p.

Root-Knot Nematode Parasitism Suppresses Host RNA Silencing

Root-knot nematodes damage crops around the world by developing complex feeding sites from normal root cells of their hosts. The ability to initiate and maintain this feeding site (composed of individual "giant cells") is essential to their parasitism process. RNA silencing pathways in plants serve a diverse set of functions, from directing growth and development to defending against invading pathogens. Influencing a host's RNA silencing pathways as a pathogenicity strategy has been well-documented for viral plant pathogens, but recently, it has become clear that silencing pathways also play an important role in other plant pathosystems. To determine if RNA silencing pathways play a role in nematode parasitism, we tested the susceptibility of plants that express a viral suppressor of RNA silencing. We observed an increase in susceptibility to nematode parasitism in plants expressing viral suppressors of RNA silencing. Results from studies utilizing a silenced reporter gene suggest that active suppression of RNA silencing pathways may be occurring during nematode parasitism. With these studies, we provide further evidence to the growing body of plant-biotic interaction research that suppression of RNA silencing is important in the successful interaction between a plant-parasitic animal and its host.

Lost in translation? microRNAs at the rough ER

MicroRNAs (miRNAs) function to post-transcriptionally regulate target RNAs, including long non-coding RNAs and mRNAs. A recent study demonstrates that Arabidopsis miRNAs are enriched at the rough endoplasmic reticulum (ER). This enrichment is a surprise, given that most known miRNA targets are not expected to be translated at the rough ER.

An Arabidopsis NAC transcription factor NAC4 promotes pathogen-induced cell death under negative regulation by microRNA164

Hypersensitive response (HR) is a form of programmed cell death (PCD) and the primary immune response that prevents pathogen invasion in plants. Here, we show that a microRNAmiR164 and its target gene NAC4 (At5g07680), encoding a NAC transcription factor, play essential roles in the regulation of HR PCD in Arabidopsis thaliana. Cell death symptoms were noticeably enhanced in NAC4-overexpressing (35S:NAC4) and mir164 mutant plants in response to avirulent bacterial pathogens. NAC4 expression was induced by pathogen infection and negatively regulated by miR164 expression. NAC4-binding DNA sequences were determined by in vitro binding site selection using random oligonucleotide sequences. Microarray, chromatin immunoprecipitation and quantitative real time polymerase chain reaction (qRT-PCR) analyses, followed by cell death assays in protoplasts, led to the identification of NAC4 target genes LURP1, WRKY40 and WRKY54, which act as negative regulators of cell death. Our results suggest that NAC4 promotes hypersensitive cell death by suppressing its target genes and this immune process is fine-tuned by the negative action of miR164.