Identification of new stress-induced microRNA and their targets in wheat using computational approach

Early changes in microRNA expression in Arabidopsis plants infected with the fungal pathogen Fusarium graminearum

Plants respond to biotic stressors by modulating various processes in an attempt to limit the attack by a pathogen or herbivore. Triggering these different defense processes requires orchestration of a network of proteins and RNA molecules that includes microRNAs (miRNAs). These short RNA molecules (20-22 nucleotides) have been shown to be important players in the early responses of plants to stresses because they can rapidly regulate the expression levels of a network of downstream genes. The ascomycete Fusarium graminearum is an important fungal pathogen that causes significant losses in cereal crops worldwide. Using the well-characterized Fusarium-Arabidopsis pathosystem, we investigated how plants change expression of their miRNAs globally during the early stages of infection by F. graminearum. We have created a catalog of miRNAs that have differential expression in infected samples even before any visual symptoms of the infection are present. In addition to miRNAs that have been previously implicated in stress responses, we have also identified evolutionarily young miRNAs whose levels change significantly in response to fungal infection. Some of these young miRNAs have homologs present in cereals, which suggest that some of these miRNAs could be drivers of stress response. By examining if the miRNAs in this catalog have causal roles in plant infection response, a unique path toward development of plants with increased resistance to fungal pathogens can be developed.

Early changes in microRNA expression in Arabidopsis plants infected with the fungal pathogen Fusarium graminearum

Plants respond to biotic stressors by modulating various processes in an attempt to limit the attack by a pathogen or herbivore. Triggering these different defense processes requires orchestration of a network of proteins and RNA molecules that includes microRNAs (miRNAs). These short RNA molecules (20-22 nucleotides) have been shown to be important players in the early responses of plants to stresses because they can rapidly regulate the expression levels of a network of downstream genes. The ascomycete Fusarium graminearum is an important fungal pathogen that causes significant losses in cereal crops worldwide. Using the well-characterized Fusarium-Arabidopsis pathosystem, we investigated how plants change expression of their miRNAs globally during the early stages of infection by F. graminearum. In addition to miRNAs that have been previously implicated in stress responses, we have also identified evolutionarily young miRNAs whose levels change significantly in response to fungal infection. Some of these young miRNAs have homologs present in cereals. Thus, manipulating expression of these miRNAs may provide a unique path toward development of plants with increased resistance to fungal pathogens.

Genome-Wide Identification and Expression Profiling of the ABF Transcription Factor Family in Wheat (Triticum aestivum L.)

Members of the abscisic acid (ABA)-responsive element (ABRE) binding factor (ABF) and ABA-responsive element binding protein (AREB) families play essential roles in the regulation of ABA signaling pathway activity and shape the ability of plants to adapt to a range of stressful environmental conditions. To date, however, systematic genome-wide analyses focused on the ABF/AREB gene family in wheat are lacking. Here, we identified 35 ABF/AREB genes in the wheat genome, designated TaABF1-TaABF35 according to their chromosomal distribution. These genes were further classified, based on their phylogenetic relationships, into three groups (A-C), with the TaABF genes in a given group exhibiting similar motifs and similar numbers of introns/exons. Cis-element analyses of the promoter regions upstream of these TaABFs revealed large numbers of ABREs, with the other predominant elements that were identified differing across these three groups. Patterns of TaABF gene expansion were primarily characterized by allopolyploidization and fragment duplication, with purifying selection having played a significant role in the evolution of this gene family. Further expression profiling indicated that the majority of the TaABF genes from groups A and B were highly expressed in various tissues and upregulated following abiotic stress exposure such as drought, low temperature, low nitrogen, etc., while some of the TaABF genes in group C were specifically expressed in grain tissues. Regulatory network analyses revealed that four of the group A TaABFs (TaABF2, TaABF7, TaABF13, and TaABF19) were centrally located in protein-protein interaction networks, with 13 of these TaABF genes being regulated by 11 known miRNAs, which play important roles in abiotic stress resistance such as drought and salt stress. The two primary upstream transcription factor types found to regulate TaABF gene expression were BBR/BPC and ERF, which have previously been reported to be important in the context of plant abiotic stress responses. Together, these results offer insight into the role that the ABF/AREB genes play in the responses of wheat to abiotic stressors, providing a robust foundation for future functional studies of these genes.

Plant responses to metals stress: microRNAs in focus

Metal toxicity can largely affect the growth and yield of numerous plant species. Plants have developed specific mechanisms to withstand the varying amounts of metals. One approach involves utilization of microRNAs (miRNAs) that are known for cleaving transcripts or inhibiting translation to mediate post-transcriptional control. Use of transcription factors (TFs) or gene regulation in metal detoxification largely depends on metal-responsive miRNAs. Moreover, systemic signals and physiological processes for plants response to metal toxicities are likewise controlled by miRNAs. Therefore, it is necessary to understand miRNAs and their regulatory networks in relation to metal stress. The miRNA-based approach can be important to produce metal-tolerant plant species. Here, we have reviewed the importance of plant miRNAs and their role in mitigating metal toxicities. The current review also discusses the specific advances that have occurred as a result of the identification and validation of several metal stress-responsive miRNAs.

Differential expression profiling of microRNAs and their target genes during wheat-Bipolaris sorokiniana pathosystem

Wheat spot blotch, caused by Bipolaris sorokiniana, is a serious constraint to wheat production, reducing grain yield and consequently having severe economic impact. Several plant miRNAs have recently been discovered as regulators of gene expression involved in cellular and metabolic functions. So far reports on the roles of miRNAs in B. sorokiniana infection response of wheat are scanty. To further understand the defence mechanism of miRNAs- regulated cellular functions, we examined the expression patterns of 17 miRNAs and their targets involved in the interaction between wheat and B. sorokiniana in two contrasting wheat genotypes, Chiriya-1 and WH-147. All of the miRNAs and target genes were shown to be expressed differentially in both genotypes after B. sorokiniana infection. Seven and nine miRNAs were observed as up-regulated in the resistant genotype Chiriya-1 and the susceptible genotype WH147, respectively. Among the up-regulated miRNAs, ptc-miR901 (~ 10.21 times) accumulated the most in Chiriya-1 followed by ptc-miR1450 (~ 7.6 times) in WH-147. Furthermore, only two miRNAs, tae-miR156 and ptc-miR482c showed a complete inverse relation with their target genes, SPL and NBS-LRR, respectively. This research sheds light on the temporal differential regulation of miRNAs and their targets, which may play a role in wheat adaptation to B. sorokiniana infection.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01092-1.

Current status of microRNA-mediated regulation of drought stress responses in cereals

Drought is one of the most important abiotic stress factors impeding crop productivity. With the uncovering of their role as potential regulators of gene expression, microRNAs (miRNAs) have been recognized as new targets for developing stress resistance. MicroRNAs are small noncoding RNAs whose abundance is significantly altered under stress conditions. Interestingly, plant miRNAs predominantly targets transcription factors (TFs), and some of which are also the most critical drought-responsive genes that in turn could regulate the expression of numerous loci with drought-adaptive potential. The phytohormone ABA plays important roles in regulating stomatal conductance and in initiating an adaptive response to drought stress. miRNAs are implicated in regulating ABA-(abscisic acid) and non-ABA-mediated drought resistance pathways. For instance, miR159-MYB module and miR169-NFYA module participates in an ABA-dependent pathway, whereas several other ABA-independent miRNA-target modules (miR156-SPL; miR393-TIR1; miR160-ARF10, ARF16, ARF17; miR167-ARF6 and ARF8; miR390/TAS3siRNA-ARF2, ARF3, ARF4) collectively regulate drought responses in plants. Overall, miRNA-mediated drought response manifests diverse molecular, biochemical and physiological processes. Because of their immense role in controlling gene expression, miRNA manipulation has significant potential to augment plant tolerance to drought stress. This review compiles the current understanding of drought-responsive miRNAs in major cereals. Also, potential miRNA manipulation strategies currently in use along with the challenges and future perspectives are discussed.

Identification and expression analysis of some wheat F-box subfamilies during plant development and infection by Puccinia triticina

As one of the largest protein families in plants, F-box proteins are involved in many important cellular processes. Until now, a limited number of investigations have been conducted on wheat F-box genes due to its variable structure and large and polyploid genome. Classification, identification, structural analysis, evolutionary relationship, and chromosomal distribution of some wheat F-box genes are described in the present study. A total number of 1013 potential F-box proteins which are encoded by 409 genes was identified in wheat, and classified into 12 subfamilies based on their C-terminal domain structures. Furthermore, proteins with identical or similar C-terminal domain were clustered together. Location of 409 F-box genes was identified on all 21 wheat chromosomes but showed an uneven distribution. Segmental duplication was the main reason for the increase in the number of wheat F-box genes. Gene expression analysis based on digital PCR showed that most of the F-box genes were highly expressed in the later development stages of wheat, including the formation of spike, grain, flag leaf, and participated in drought stress (DS), heat stress (HS), and their combination (HD). Of the nine F-box genes we investigated using quantitative PCR (qPCR) following fungal pathogen infection, five were involved in wheat resistance to the infection by leaf rust pathogen and one in the susceptible response. These results provide important information on wheat F-box proteins for further functional studies, especially the proteins that played roles in response to heat and drought stresses and leaf rust pathogen infection.

Drought Response in Rice: The miRNA Story

As a semi-aquatic plant, rice requires water for proper growth, development, and orientation of physiological processes. Stress is induced at the cellular and molecular level when rice is exposed to drought or periods of low water availability. Plants have existing defense mechanisms in planta that respond to stress. In this review we examine the role played by miRNAs in the regulation and control of drought stress in rice through a summary of molecular studies conducted on miRNAs with emphasis on their contribution to drought regulatory networks in comparison to other plant systems. The interaction between miRNAs, target genes, transcription factors and their respective roles in drought-induced stresses is elaborated. The cross talk involved in controlling drought stress responses through the up and down regulation of targets encoding regulatory and functional proteins is highlighted. The information contained herein can further be explored to identify targets for crop improvement in the future.

Identification and characterization of CircRNAs involved in the regulation of wheat root length

BACKGROUND

Recent studies indicate that circular RNAs (circRNAs) may play important roles in the regulation of plant growth and development. Plant roots are the main organs of nutrient and water uptake. However, whether circRNAs involved in the regulation of plant root growth remains to be elucidated.

METHODS

LH9, XN979 and YN29 are three Chinese wheat varieties with contrasting root lengths. Here, the root circRNA expression profiles of LH9, XN979 and YN29 were examined by using high-throughput sequencing technology.

RESULTS

Thirty-three and twenty-two differentially expressed circRNAs (DECs) were identified in the YN29-LH9 comparison and YN29-XN979 comparison, respectively. Among them, ten DECs coexisted in both comparisons. As the roots of both LH9 and XN979 were significantly larger and deeper than YN29, the ten DECs coexisting in the two comparisons were highly likely to be involved in the regulation of wheat root length. Moreover, three of the ten DECs have potential miRNA binding sites. Real-time PCR analysis showed that the expression levels of the potential binding miRNAs exhibited significant differences between the long root plants and the short root plants.

CONCLUSIONS

The expression levels of some circRNAs exhibited significant differences in wheat varieties with contrasting root phenotypes. Ten DECs involved in the regulation of wheat root length were successfully identified in which three of them have potential miRNAs binding sites. The expression levels of putative circRNA-binding miRNAs were correlated with their corresponding circRNAs. Our results provide new clues for studying the potential roles of circRNAs in the regulation of wheat root length.

Long noncoding RNAs in the model species Brachypodium distachyon

Eukaryotic genomes are pervasively transcribed and only a small portion of the transcribed sequences belongs to protein coding genes. High-throughput sequencing technology contributed to consolidate this perspective, allowing the identification of numerous noncoding RNAs with key roles in biological processes. Long noncoding RNAs (lncRNAs) are transcripts longer than 200 nt with limited phylogenetic conservation, expressed at low levels and characterized by tissue/organ specific expression profiles. Although a large set of lncRNAs has been identified, the functional roles of lncRNAs are only beginning to be recognized and the molecular mechanism of lncRNA-mediated gene regulation remains largely unexplored, particularly in plants where their annotation and characterization are still incomplete. Using public and proprietary poly-(A)+ RNA-seq data as well as a collection of full length ESTs from several organs, developmental stages and stress conditions in three Brachypodium distachyon inbred lines, we describe the identification and the main features of thousands lncRNAs. Here we provide a genome-wide characterization of lncRNAs, highlighting their intraspecies conservation and describing their expression patterns among several organs/tissues and stress conditions. This work represents a fundamental resource to deepen our knowledge on long noncoding RNAs in C3 cereals, allowing the Brachypodium community to exploit these results in future research programs.

Extrapolative microRNA precursor based SSR mining from tea EST database in respect to agronomic traits

Tea (Camellia sinensis, (L.) Kuntze) is considered as most popular drink across the world and it is widely consumed beverage for its several health-benefit characteristics. These positive traits primarily rely on its regulatory networks of different metabolic pathways. Development of microsatellite markers from the conserved genomic regions are being worthwhile for reviewing the genetic diversity of closely related species or self-pollinated species. Although several SSR markers have been reported, in tea, the trait-specific Simple Sequence Repeat (SSR) markers, leading to be useful in marker assisted breeding technique, are yet to be identified. Micro RNAs are short, non-coding RNA molecules, involved in post transcriptional mode of gene regulation and thus effects on related phenotype. Present study deals with identification of the microsatellite motifs within the reported and predicted miRNA precursors that are effectively followed by designing of primers from SSR flanking regions in order to PCR validation. In addition to the earlier reports, two new miRNAs are predicting here from tea expressed tag sequence database. Furthermore, 18 SSR motifs are found to be in 13 of all 33 predicted miRNAs. Trinucleotide motifs are most abundant among all followed by dinucleotides. Since, miRNA based SSR markers are evidenced to have significant role on genetic fingerprinting study, these outcomes would pave the way in developing novel markers for tagging tea specific agronomic traits as well as substantiating non-conventional breeding program.

Regulation of Isoflavone Biosynthesis by miRNAs in Two Contrasting Soybean Genotypes at Different Seed Developmental Stages

Owing to the presence of nutritionally important, health-promoting bioactive compounds, especially isoflavones, soybean has acquired the status of a functional food. miRNAs are tiny riboregulator of gene expression by either decreasing and/or increasing the expression of their corresponding target genes. Despite several works on identification and functional characterization of plant miRNAs, the role of miRNAs in the regulation of isoflavones metabolism is still a virgin field. In the present study, we identified a total of 31 new miRNAs along with their 245 putative target genes from soybean seed-specific ESTs using computational approach. The Kyoto Encyclopedia of Genes and Genomes pathway analyses indicated that miRNA putatively regulates metabolism and genetic information processing. Out of that, a total of 5 miRNAs (Gma-miRNA12, Gma-miRNA24, Gma-miRNA26, Gma-miRNA28, and Gma-miRNA29) were predicted and validated for their probable role during isoflavone biosynthesis. We also validated their five target genes using RA-PCR, which is as good as 5'RLM-RACE. Temporal regulation [35 days after flowering, 45, 55, and 65 DAF] of miRNAs and their targets showed differential expression schema. Differential expression of Gma-miR26 and Gma-miRNA28 along with their corresponding target genes (Glyma.10G197900 and Glyma.09G127200) showed a direct relationship with the total isoflavone content. Therefore, understanding the miRNA-based genetic regulation of isoflavone pathway would assist in selection and manipulation to get high-performing soybean genotypes with better isoflavone yield.

Functional Roles of microRNAs in Agronomically Important Plants-Potential as Targets for Crop Improvement and Protection

MicroRNAs (miRNAs) are a class of small non-coding RNAs that have recently emerged as important regulators of gene expression, mainly through cleavage and/or translation inhibition of the target mRNAs during or after transcription. miRNAs play important roles by regulating a multitude of biological processes in plants which include maintenance of genome integrity, development, metabolism, and adaptive responses toward environmental stresses. The increasing population of the world and their food demands requires focused efforts for the improvement of crop plants to ensure sustainable food production. Manipulation of mRNA transcript abundance via miRNA control provides a unique strategy for modulating differential plant gene expression and miRNAs are thus emerging as the next generation targets for genetic engineering for improvement of the agronomic properties of crops. However, a deeper understanding of its potential and the mechanisms involved will facilitate the design of suitable strategies to obtain the desirable traits with minimum trade-offs in the modified crops. In this regard, this review highlights the diverse roles of conserved and newly identified miRNAs in various food and industrial crops and recent advances made in the uses of miRNAs to improve plants of agronomically importance so as to significantly enhance crop yields and increase tolerance to various environmental stress agents of biotic-or abiotic origin.

Dissecting miRNAs in Wheat D Genome Progenitor, Aegilops tauschii

As the post-transcriptional regulators of gene expression, microRNAs or miRNAs comprise an integral part of understanding how genomes function. Although miRNAs have been a major focus of recent efforts, miRNA research is still in its infancy in most plant species. Aegilops tauschii, the D genome progenitor of bread wheat, is a wild diploid grass exhibiting remarkable population diversity. Due to the direct ancestry and the diverse gene pool, A. tauschii is a promising source for bread wheat improvement. In this study, a total of 87 Aegilops miRNA families, including 51 previously unknown, were computationally identified both at the subgenomic level, using flow-sorted A. tauschii 5D chromosome, and at the whole genome level. Predictions at the genomic and subgenomic levels suggested A. tauschii 5D chromosome as rich in pre-miRNAs that are highly associated with Class II DNA transposons. In order to gain insights into miRNA evolution, putative 5D chromosome miRNAs were compared to its modern ortholog, Triticum aestivum 5D chromosome, revealing that 48 of the 58 A. tauschii 5D miRNAs were conserved in orthologous T. aestivum 5D chromosome. The expression profiles of selected miRNAs (miR167, miR5205, miR5175, miR5523) provided the first experimental evidence for miR5175, miR5205 and miR5523, and revealed differential expressional changes in response to drought in different genetic backgrounds for miR167 and miR5175. Interestingly, while miR5523 coding regions were present and expressed as pre-miR5523 in both T. aestivum and A. tauschii, the expression of mature miR5523 was observed only in A. tauschii under normal conditions, pointing out to an interference at the downstream processing of pre-miR5523 in T. aestivum. Overall, this study expands our knowledge on the miRNA catalog of A. tauschii, locating a subset specifically to the 5D chromosome, with ample functional and comparative insight which should contribute to and complement efforts to develop drought tolerant wheat varieties.

Role of bioinformatics in establishing microRNAs as modulators of abiotic stress responses: the new revolution

microRNAs (miRs) are a class of 21-24 nucleotide long non-coding RNAs responsible for regulating the expression of associated genes mainly by cleavage or translational inhibition of the target transcripts. With this characteristic of silencing, miRs act as an important component in regulation of plant responses in various stress conditions. In recent years, with drastic change in environmental and soil conditions different type of stresses have emerged as a major challenge for plants growth and productivity. The identification and profiling of miRs has itself been a challenge for research workers given their small size and large number of many probable sequences in the genome. Application of computational approaches has expedited the process of identification of miRs and their expression profiling in different conditions. The development of High-Throughput Sequencing (HTS) techniques has facilitated to gain access to the global profiles of the miRs for understanding their mode of action in plants. Introduction of various bioinformatics databases and tools have revolutionized the study of miRs and other small RNAs. This review focuses the role of bioinformatics approaches in the identification and study of the regulatory roles of plant miRs in the adaptive response to stresses.

De novo transcriptome analysis of Medicago falcata reveals novel insights about the mechanisms underlying abiotic stress-responsive pathway

Background

The entire world is facing a deteriorating environment. Understanding the mechanisms underlying plant responses to external abiotic stresses is important for breeding stress-tolerant crops and herbages. Phytohormones play critical regulatory roles in plants in the response to external and internal cues to regulate growth and development. Medicago falcata is one of the stress-tolerant candidate leguminous species and is able to fix atmospheric nitrogen. This ability allows leguminous plants to grow in nitrogen deficient soils.

Methods

We performed Illumina sequencing of cDNA prepared from abiotic stress treated M. falcata. Sequencedreads were assembled to provide a transcriptome resource. Transcripts were annotated using BLASTsearches against the NCBI non-redundant database and gene ontology definitions were assigned. Acomparison among the three abiotic stress treated samples was carried out. The expression of transcriptswas confirmed with qRT-PCR.

Results

We present an abiotic stress-responsive M. falcata transcriptome using next-generation sequencing data from samples grown under standard, dehydration, high salinity, and cold conditions. We combined reads from all samples and de novo assembled 98,515 transcripts to build the M. falcata gene index. A comprehensive analysis of the transcriptome revealed abiotic stress-responsive mechanisms underlying the metabolism and core signalling components of major phytohormones. We identified nod factor signalling pathways during early symbiotic nodulation that are modified by abiotic stresses. Additionally, a global comparison of homology between the M. falcata and M. truncatula transcriptomes, along with five other leguminous species, revealed a high level of global sequence conservation within the family.

Conclusions

M. falcata is shown to be a model candidate for studying abiotic stress-responsive mechanisms in legumes. This global gene expression analysis provides new insights into the biochemical and molecular mechanisms involved in the acclimation to abiotic stresses. Our data provides many gene candidates that might be used for herbage and crop breeding. Additionally, FalcataBase (http://bioinformatics.cau.edu.cn/falcata/) was built for storing these data.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2019-x) contains supplementary material, which is available to authorized users.

Combined Small RNA and Degradome Sequencing Reveals Novel MiRNAs and Their Targets in the High-Yield Mutant Wheat Strain Yunong 3114

Wheat is one of the main food sources worldwide; large amount studies have been conducted to improve wheat production. MicroRNAs (miRNAs) with about 20-30 nucleotide are a class of regulatory small RNAs (sRNAs), which could regulate gene expression through sequence-specific base pairing with target mRNAs, playing important roles in plant growth. An ideal plant architecture (IPA) is crucial to enhance yield in bread wheat. In this study, the high-yield wheat strain Yunong 3114 was EMS-mutagenesis from the wild-type strain Yunong 201, exhibiting a preferable plant structure compared with the wild-type strain. We constructed small RNA and degradome libraries from Yunong 201 and Yunong 3114, and performed small RNA sequencing of these libraries in order identify miRNAs and their targets related to IPA in wheat. Totally, we identified 488 known and 837 novel miRNAs from Yunong 3114 and 391 known and 533 novel miRNAs from Yunong 201. The number of miRNAs in the mutant increased. A total of 37 known and 432 putative novel miRNAs were specifically expressed in the mutant strain; furthermore, 23 known and 159 putative novel miRNAs were specifically expressed in the wild-type strain. A total of 150 known and 100 novel miRNAs were differentially expressed between mutant and wild-type strains. Among these differentially expressed novel miRNAs, 4 and 8 predict novel miRNAs were evidenced by degradome sequencing and showed up-regulated and down-regulated expressions in the mutant strain Yunong 3114, respectively. Targeted gene annotation and previous results indicated that this set of miRNAs is related to plant structure. Our results further suggested that miRNAs may be necessary to obtain an optimal wheat structure.

miRNA-based drought regulation in wheat

MicroRNAs (miRNAs) are a class of small non-coding regulatory RNAs that regulate gene expression by guiding target mRNA cleavage or translational inhibition. Drought is a common environmental stress influencing crop growth and development. To date, it has been reported that a number of plant miRNA are involved in drought stress response. In this study, we comparatively investigated drought stress-responsive miRNAs in the root and leaf of bread wheat (Triticum aestivum cv. Sivas 111/33) by miRNA microarray screening. miRNA microarray analysis showed that 285 miRNAs (207 upregulated and 78 downregulated) and 244 miRNAs (115 upregulated and 129 downregulated) were differentially expressed in leaf and root tissues, respectively. Among the differentially expressed miRNAs, 23 miRNAs were only expressed in the leaf and 26 miRNAs were only expressed in the root of wheat growth under drought stress. Upon drought treatment, expression of miR159, miR160, miR166, miR169, miR172, miR395, miR396, miR408, miR472, miR477, miR482, miR1858, miR2118, and miR5049 were found to be significantly differentiated in bread wheat. The regulatory network analysis showed that miR395 has connections with a number of target transcripts, and miR159 and miR319 share a number of target genes. Drought-tolerant and drought-sensitive wheat cultivars showed altered expression pattern upon drought stress in terms of investigated miRNA and their target transcript expression level.

Harnessing NGS and Big Data Optimally: Comparison of miRNA Prediction from Assembled versus Non-assembled Sequencing Data--The Case of the Grass Aegilops tauschii Complex Genome

MicroRNAs (miRNAs) are small, endogenous, non-coding RNA molecules that regulate gene expression at the post-transcriptional level. As high-throughput next generation sequencing (NGS) and Big Data rapidly accumulate for various species, efforts for in silico identification of miRNAs intensify. Surprisingly, the effect of the input genomics sequence on the robustness of miRNA prediction was not evaluated in detail to date. In the present study, we performed a homology-based miRNA and isomiRNA prediction of the 5D chromosome of bread wheat progenitor, Aegilops tauschii, using two distinct sequence data sets as input: (1) raw sequence reads obtained from 454-GS FLX Titanium sequencing platform and (2) an assembly constructed from these reads. We also compared this method with a number of available plant sequence datasets. We report here the identification of 62 and 22 miRNAs from raw reads and the assembly, respectively, of which 16 were predicted with high confidence from both datasets. While raw reads promoted sensitivity with the high number of miRNAs predicted, 55% (12 out of 22) of the assembly-based predictions were supported by previous observations, bringing specificity forward compared to the read-based predictions, of which only 37% were supported. Importantly, raw reads could identify several repeat-related miRNAs that could not be detected with the assembly. However, raw reads could not capture 6 miRNAs, for which the stem-loops could only be covered by the relatively longer sequences from the assembly. In summary, the comparison of miRNA datasets obtained by these two strategies revealed that utilization of raw reads, as well as assemblies for in silico prediction, have distinct advantages and disadvantages. Consideration of these important nuances can benefit future miRNA identification efforts in the current age of NGS and Big Data driven life sciences innovation.

An integrative approach to identify hexaploid wheat miRNAome associated with development and tolerance to abiotic stress

Background

Wheat is a major staple crop with broad adaptability to a wide range of environmental conditions. This adaptability involves several stress and developmentally responsive genes, in which microRNAs (miRNAs) have emerged as important regulatory factors. However, the currently used approaches to identify miRNAs in this polyploid complex system focus on conserved and highly expressed miRNAs avoiding regularly those that are often lineage-specific, condition-specific, or appeared recently in evolution. In addition, many environmental and biological factors affecting miRNA expression were not yet considered, resulting still in an incomplete repertoire of wheat miRNAs.

Results

We developed a conservation-independent technique based on an integrative approach that combines machine learning, bioinformatic tools, biological insights of known miRNA expression profiles and universal criteria of plant miRNAs to identify miRNAs with more confidence. The developed pipeline can potentially identify novel wheat miRNAs that share features common to several species or that are species specific or clade specific. It allowed the discovery of 199 miRNA candidates associated with different abiotic stresses and development stages. We also highlight from the raw data 267 miRNAs conserved with 43 miRBase families. The predicted miRNAs are highly associated with abiotic stress responses, tolerance and development. GO enrichment analysis showed that they may play biological and physiological roles associated with cold, salt and aluminum (Al) through auxin signaling pathways, regulation of gene expression, ubiquitination, transport, carbohydrates, gibberellins, lipid, glutathione and secondary metabolism, photosynthesis, as well as floral transition and flowering.

Conclusion

This approach provides a broad repertoire of hexaploid wheat miRNAs associated with abiotic stress responses, tolerance and development. These valuable resources of expressed wheat miRNAs will help in elucidating the regulatory mechanisms involved in freezing and Al responses and tolerance mechanisms as well as for development and flowering. In the long term, it may help in breeding stress tolerant plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1490-8) contains supplementary material, which is available to authorized users.

Post-transcriptional and post-translational regulations of drought and heat response in plants: a spider's web of mechanisms

Drought and heat tolerance are complex quantitative traits. Moreover, the adaptive significance of some stress-related traits is more related to plant survival than to agronomic performance. A web of regulatory mechanisms fine-tunes the expression of stress-related traits and integrates both environmental and developmental signals. Both post-transcriptional and post-translational modifications contribute substantially to this network with a pivotal regulatory function of the transcriptional changes related to cellular and plant stress response. Alternative splicing and RNA-mediated silencing control the amount of specific transcripts, while ubiquitin and SUMO modify activity, sub-cellular localization and half-life of proteins. Interactions across these modification mechanisms ensure temporally and spatially appropriate patterns of downstream-gene expression. For key molecular components of these regulatory mechanisms, natural genetic diversity exists among genotypes with different behavior in terms of stress tolerance, with effects upon the expression of adaptive morphological and/or physiological target traits.

Novel and conserved heat-responsive microRNAs in wheat (Triticum aestivum L.)

MicroRNAs (miRNAs) are small endogenous RNAs of ~22 nucleotides that have been shown to play regulatory role by negatively affecting the expression of genes at the post-transcriptional level. Information of miRNAs on some important crops like soybean, Arabidopsis, and rice, etc. are available, but no study on heat-responsive novel miRNAs has yet been reported in wheat (Triticum aestivum L.). In the present investigation, a popular wheat cultivar HD2985 was used in small RNA library construction and Illumina HiSeq 2000 was used to perform high-throughput sequencing of the library after cluster generation; 110,896,604 and 87,743,861 reads were generated in the control (22 °C) and heat-treated (42 °C for 2 h) samples, respectively. Forty-four precursor and mature miRNAs were found in T. aestivum from miRBase v 19. The frequencies of the miRNA families varied from 2 (tae-miR1117) to 60,672 (tae-miR159b). We identify 1052 and 902 mature miRNA sequences in HD2985 control and HS-treated samples by mapping on reference draft genome of T. aestivum. Maximum identified miRNAs were located on IWGSC_CSS_3B_scaff (chromosome 3B). We could identify 53 and 46 mature miRNA in the control and HS samples and more than 516 target genes by mapping on the reference genome of Oryza sativa, Zea mays, and Sorghum bicolor. Using different pipelines and plant-specific criteria, 37 novel miRNAs were identified in the control and treated samples. Six novel miRNA were validated using qRT-PCR to be heat-responsive. A negative correlation was, however, observed between the expression of novel miRNAs and their targets. Target prediction and pathway analysis revealed their involvement in the heat stress tolerance. These novel miRNAs are new additions to miRNA database of wheat, and the regulatory network will be made use of in deciphering the mechanism of thermotolerance in wheat.

Genome-wide fungal stress responsive miRNA expression in wheat

MicroRNAs (miRNAs) are small non-coding class of RNAs. They were identified in many plants with their diverse regulatory roles in several cellular and metabolic processes. A number of miRNAs were involved in biotic and abiotic stress responses. Here, fungal stress responsive wheat miRNAs were analyzed by using miRNA-microarray strategy. Two different fungi (Fusarium culmorum and Bipolaris sorokiniana) were inoculated on resistant and sensitive wheat cultivars. A total of 87 differentially regulated miRNAs were detected in the 8 × 15 K array including all of the available plant miRNAs. Using bioinformatics tools, the target transcripts of responsive miRNAs were predicted, and related biological processes and mechanisms were assessed. A number of the miRNAs such as miR2592s, miR869.1, miR169b were highly differentially regulated showing more than 200-fold change upon fungal-inoculation. Some of the miRNAs were identified as fungal-inoculation responsive for the first time. The analyses showed that some of the differentially regulated miRNAs targeted resistance-related genes such as LRR, glucuronosyl transferase, peroxidase and Pto kinase. The comparison of the two miRNA-microarray analyses indicated that fungal-responsive wheat miRNAs were differentially regulated in pathogen- and cultivar-specific manners.

History and current status of wheat miRNAs using next-generation sequencing and their roles in development and stress

As small molecules that aid in posttranscriptional silencing, microRNA (miRNA) discovery and characterization have vastly benefited from the recent development and widespread application of next-generation sequencing (NGS) technologies. Several miRNAs were identified through sequencing of constructed small RNA libraries, whereas others were predicted by in silico methods using the recently accumulating sequence data. NGS was a major breakthrough in efforts to sequence and dissect the genomes of plants, including bread wheat and its progenitors, which have large, repetitive and complex genomes. Availability of survey sequences of wheat whole genome and its individual chromosomes enabled researchers to predict and assess wheat miRNAs both in the subgenomic and whole genome levels. Moreover, small RNA construction and sequencing-based studies identified several putative development- and stress-related wheat miRNAs, revealing their differential expression patterns in specific developmental stages and/or in response to stress conditions. With the vast amount of wheat miRNAs identified in recent years, we are approaching to an overall knowledge on the wheat miRNA repertoire. In the following years, more comprehensive research in relation to miRNA conservation or divergence across wheat and its close relatives or progenitors should be performed. Results may serve valuable in understanding both the significant roles of species-specific miRNAs and also provide us information in relation to the dynamics between miRNAs and evolution in wheat. Furthermore, putative development- or stress-related miRNAs identified should be subjected to further functional analysis, which may be valuable in efforts to develop wheat with better resistance and/or yield.

Differential regulation of microRNAs in response to osmotic, salt and cold stresses in wheat

MicroRNAs (miRNAs) are tiny non-coding regulatory molecules that modulate plant's gene expression either by cleaving or repressing their mRNA targets. To unravel the plant actions in response to various environmental factors, identification of stress related miRNAs is essential. For understanding the regulatory behaviour of various abiotic stresses and miRNAs in wheat genotype C-306, we examined expression profile of selected conserved miRNAs viz. miR159, miR164, miR168, miR172, miR393, miR397, miR529 and miR1029 tangled in adapting osmotic, salt and cold stresses. The investigation revealed that two miRNAs (miR168, miR397) were down-regulated and miR172 was up-regulated under all the stress conditions. However, miR164 and miR1029 were up-regulated under cold and osmotic stresses in contrast to salt stress. miR529 responded to cold alone and does not change under osmotic and salt stress. miR393 showed up-regulation under osmotic and salt, and down-regulation under cold stress indicating auxin based differential cold response. Variation in expression level of studied miRNAs in presence of target genes delivers a likely elucidation of miRNAs based abiotic stress regulation. In addition, we reported new stress induced miRNAs Ta-miR855 using computational approach. Results revealed first documentation that miR855 is regulated by salinity stress in wheat. These findings indicate that diverse miRNAs were responsive to osmotic, salt and cold stress and could function in wheat response to abiotic stresses.

New wheat microRNA using whole-genome sequence

MicroRNAs are post-transcriptional regulators of gene expression, taking roles in a variety of fundamental biological processes. Hence, their identification, annotation and characterization are of great significance, especially in bread wheat, one of the main food sources for humans. The recent availability of 5× coverage Triticum aestivum L. whole-genome sequence provided us with the opportunity to perform a systematic prediction of a complete catalogue of wheat microRNAs. Using an in silico homology-based approach, stem-loop coding regions were derived from two assemblies, constructed from wheat 454 reads. To avoid the presence of pseudo-microRNAs in the final data set, transposable element related stem-loops were eliminated by repeat analysis. Overall, 52 putative wheat microRNAs were predicted, including seven, which have not been previously published. Moreover, with distinct analysis of the two different assemblies, both variety and representation of putative microRNA-coding stem-loops were found to be predominant in the intergenic regions. By searching available expressed sequences and small RNA library databases, expression evidence for 39 (out of 52) putative wheat microRNAs was provided. Expression of three of the predicted microRNAs (miR166, miR396 and miR528) was also comparatively quantified with real-time quantitative reverse transcription PCR. This is the first report on in silico prediction of a whole repertoire of bread wheat microRNAs, supported by the wet-lab validation.