Stress responsive miRNAs and isomiRs in cereals

An intelligent model for prediction of abiotic stress-responsive microRNAs in plants using statistical moments based features and ensemble approaches

This study proposed an intelligent model for predicting abiotic stress-responsive microRNAs in plants. MicroRNAs (miRNAs) are short RNA molecules regulates the stress in genes. Experimental methods are costly and time-consuming, as compare to in-silico prediction. Addressing this gap, the study seeks to develop an efficient computational model for plant stress response prediction. The two benchmark datasets for MiRNA and Pre-MiRNA dataset have been acquired in this study. Four ensemble approaches such as bagging, boosting, stacking, and blending have been employed. Classifiers such as Random Forest (RF), Extra Trees (ET), Ada Boost (ADB), Light Gradient Boosting Machine (LGBM), and Support Vector Machine (SVM). Stacking and Blending employed all stated classifiers as base learners and Logistic Regression (LR) as Meta Classifier. There have been a total of four types of testing used, including independent set, self-consistency, cross-validation with 5 and 10 folds, and jackknife. This study has utilized evaluation metrics such as accuracy score, specificity, sensitivity, Mathew's correlation coefficient (MCC), and AUC. Our proposed methodology has outperformed existing state of the art study in both datasets based on independent set testing. The SVM-based approach has exhibited accuracy score of 0.659 for the MiRNA dataset, which is better than the previous study. The ET classifier has surpassed the accuracy of Pre-MiRNA dataset as compared to the existing benchmark study, achieving an impressive score of 0.67. The proposed method can be used in future research to predict abiotic stresses in plants.

The intricacies of isomiRs: from classification to clinical relevance

MicroRNAs (miRNAs) and isoforms of their archetype, called isomiRs, regulate gene expression via complementary base-pair binding to messenger RNAs (mRNAs). The partially evolutionarily conserved isomiR sequence variations are differentially expressed among tissues, populations, and genders, and between healthy and diseased states. Aiming towards the clinical use of isomiRs as diagnostic biomarkers and for therapeutic purposes, several challenges need to be addressed, including (i) clarification of isomiR definition, (ii) improved annotation in databases with new standardization (such as the mirGFF3 format), and (iii) improved methods of isomiR detection, functional verification, and in silico analysis. In this review we discuss the respective challenges, and highlight the opportunities for clinical use of isomiRs, especially in the light of increasing amounts of next-generation sequencing (NGS) data.

The role of small RNAs in resistant melon cultivar against Phelipanche aegyptiaca parasitization

Bidirectional trans-kingdom RNA silencing, a pivotal factor in plant-pathogen interactions, remains less explored in plant host-parasite dynamics. Here, using small RNA sequencing in melon root systems, we investigated microRNA (miRNA) expression variation in resistant and susceptible cultivars pre-and post-infection by the parasitic plant, broomrape. This approach revealed 979 known miRNAs and 110 novel miRNAs across 110 families. When comparing susceptible (F0) and resistant (R0) melon lines with broomrape infection (F25 and R25), 39 significantly differentially expressed miRNAs were observed in F25 vs. F0, 35 in R25 vs. R0, and 5 in R25 vs. F25. Notably, two miRNAs consistently exhibited differential expression across all comparisons, targeting genes linked to plant disease resistance. This suggests their pivotal role in melon's defense against broomrape. The target genes of these miRNAs were confirmed via degradome sequencing and validated by qRT-PCR, ensuring reliable sequencing outcomes. GO and KEGG analyses shed light on the molecular functions and pathways of these differential miRNAs. Furthermore, our study unveiled four trans-kingdom miRNAs, forming a foundation for exploring melon's resistance to broomrape.

miR397-LACs mediated cadmium stress tolerance in Arabidopsis thaliana

Cadmium (Cd) is a non-essential heavy metal, assimilated in plant tissue with other nutrients, disturbing the ions' homeostasis in plants. The plant develops different mechanisms to tolerate the hazardous environmental effects of Cd. Recently studies found different miRNAs that are involved in Cd stress. In the current study, miR397 mutant lines were constructed to explore the molecular mechanisms of miR397 underlying Cd tolerance. Compared with the genetically modified line of overexpressed miR397 (artificial miR397, amiR397), the lines of downregulated miR397 (Short Tandem Target Mimic miR397, STTM miR397) showed more substantial Cd tolerance with higher chlorophyll a & b, carotenoid and lignin content. ICP-OES revealed higher cell wall Cd and low total Cd levels in STTM miR397 than in the wild-type and amiR397 plants.Further, the STTM plants produced fewer reactive oxygen species (ROS) and lower activity of antioxidants enzymes (e.g., catalase [CAT], malondialdehyde [MDA]) compared with amiR397 and wild-type plants after stress, indicating that silencing the expression of miR397 can reduce oxidative damage. In addition, the different family transporters' gene expression was much higher in the amiR397 plants than in the wild type and STTM miRNA397. Our results suggest that miR397 plays a role in Cd tolerance in Arabidopsis thaliana. Overexpression of miR397 could decrease Cd tolerance in plants by regulating the expression of LAC 2/4/17, changing the lignin content, which may play an important role in inducing different stress-tolerant mechanisms and protecting the cell from a hazardous condition. This study provides a basis to elucidate the functions of miR397 and the Cd stress tolerance mechanism in Arabidopsis thaliana.

Unveiling the biosynthesis, mechanisms, and impacts of miRNAs in drought stress resilience in plants

Drought stress is one of the most serious threats to sustainable agriculture and is predicted to be further intensified in the coming decades. Therefore, understanding the mechanism of drought stress tolerance and the development of drought-resilient crops are the major goals at present. In recent years, noncoding microRNAs (miRNAs) have emerged as key regulators of gene expressions under drought stress conditions and are turning out to be the potential candidates that can be targeted to develop drought-resilient crops in the future. miRNAs are known to target and decrease the expression of various genes to govern the drought stress response in plants. In addition, emerging evidence also suggests a regulatory role of long non-coding RNAs (lncRNAs) in the regulation of miRNAs and the expression of their target genes by a process referred as miRNA sponging. In this review, we present the regulatory roles of miRNAs in the modulation of drought-responsive genes along with discussing their biosynthesis and action mechanisms. Additionally, the interactive roles of miRNAs with phytohormone signaling components have also been highlighted to present the global view of miRNA functioning under drought-stress conditions.

ASmiR: a machine learning framework for prediction of abiotic stress-specific miRNAs in plants

Abiotic stresses have become a major challenge in recent years due to their pervasive nature and shocking impacts on plant growth, development, and quality. MicroRNAs (miRNAs) play a significant role in plant response to different abiotic stresses. Thus, identification of specific abiotic stress-responsive miRNAs holds immense importance in crop breeding programmes to develop cultivars resistant to abiotic stresses. In this study, we developed a machine learning-based computational model for prediction of miRNAs associated with four specific abiotic stresses such as cold, drought, heat and salt. The pseudo K-tuple nucleotide compositional features of Kmer size 1 to 5 were used to represent miRNAs in numeric form. Feature selection strategy was employed to select important features. With the selected feature sets, support vector machine (SVM) achieved the highest cross-validation accuracy in all four abiotic stress conditions. The highest cross-validated prediction accuracies in terms of area under precision-recall curve were found to be 90.15, 90.09, 87.71, and 89.25% for cold, drought, heat and salt respectively. Overall prediction accuracies for the independent dataset were respectively observed 84.57, 80.62, 80.38 and 82.78%, for the abiotic stresses. The SVM was also seen to outperform different deep learning models for prediction of abiotic stress-responsive miRNAs. To implement our method with ease, an online prediction server "ASmiR" has been established at https://iasri-sg.icar.gov.in/asmir/ . The proposed computational model and the developed prediction tool are believed to supplement the existing effort for identification of specific abiotic stress-responsive miRNAs in plants.

MicroRNAs balance growth and salt stress responses in sweet sorghum

Salt stress is one of the major causes of reduced crop production, limiting agricultural development globally. Plants have evolved with complex systems to maintain the balance between growth and stress responses, where signaling pathways such as hormone signaling play key roles. Recent studies revealed that hormones are modulated by microRNAs (miRNAs). Previously, two sweet sorghum (Sorghum bicolor) inbred lines with different salt tolerance were identified: the salt-tolerant M-81E and the salt-sensitive Roma. The levels of endogenous hormones in M-81E and Roma varied differently under salt stress, showing a different balance between growth and stress responses. miRNA and degradome sequencing showed that the expression of many upstream transcription factors regulating signal transduction and hormone-responsive genes was directly induced by differentially expressed miRNAs, whose levels were very different between the two sweet sorghum lines. Furthermore, the effects of representative miRNAs on salt tolerance in sorghum were verified through a transformation system mediated by Agrobacterium rhizogenes. Also, miR-6225-5p reduced the level of Ca²⁺ in the miR-6225-5p-overexpressing line by inhibiting the expression of the Ca²⁺ uptake gene SbGLR3.1 in the root epidermis and affected salt tolerance in sorghum. This study provides evidence for miRNA-mediated growth and stress responses in sweet sorghum.

Multi-omics reveals the key and specific miRNA-mRNA modules underlying salt tolerance in wild emmer wheat (Triticum dicoccoides L.)

Background

Salt stress is one of the most destructive environmental factors limiting crop growth and development. MicroRNAs (miRNAs) are a class of conserved endogenous small non-coding RNAs, playing the crucial role in regulating salt response and tolerance in plants. However, the miRNAs in wild emmer wheat, especially the key and specific salt-responsive miRNAs are not well studied.

Results

Here, we performed small RNA, transcriptome, and degradome sequencing of both of salt-tolerance (ST) and salt-sensitive (SS) wild emmer genotypes to identify the miRNA-mRNA modules associating with salt tolerance. Totally, 775 miRNAs, including 361 conserved known miRNAs and 414 novel miRNAs were detected. Differential expression analysis identified 93 salt-responsive miRNAs under salt stress. Combined with RNA-seq and degradome sequencing analysis, 224 miRNA-mRNA modules displayed the complete opposite expression trends between ST and SS genotypes, most of which functionally enriched into ROS homeostasis maintaining, osmotic pressure modulating, and root growth and development. Finally, the qRT-PCR and a large-scale yeast functional screening were also performed to initially validate the expression pattern and function of candidate genes.

Conclusions

This study reported the key and specific miRNA-mRNA modules associated with salt tolerance in wild emmer, which lay the foundation for improving the salt tolerance in cultivated emmer and bread wheat through miRNA engineering approach.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08945-3.

Regulatory non-coding RNA: The core defense mechanism against plant pathogens

Plant pathogens damage crops and threaten global food security. Plants have evolved complex defense networks against pathogens, using crosstalk among various signaling pathways. Key regulators conferring plant immunity through signaling pathways include protein-coding genes and non-coding RNAs (ncRNAs). The discovery of ncRNAs in plant transcriptomes was first considered "transcriptional noise". Recent reviews have highlighted the importance of non-coding RNAs. However, understanding interactions among different types of noncoding RNAs requires additional research. This review attempts to consider how long-ncRNAs, small-ncRNAs and circular RNAs interact in response to pathogenic diseases within different plant species. Developments within genomics and bioinformatics could lead to the further discovery of plant ncRNAs, knowledge of their biological roles, as well as an understanding of their importance in exploiting the recent molecular-based technologies for crop protection.

Epigenetic marks for mitigating abiotic stresses in plants

Abiotic stressors are one of the major factors affecting agricultural output. Plants have evolved adaptive systems to respond appropriately to various environmental cues. These responses can be accomplished by modulating or fine-tuning genetic and epigenetic regulatory mechanisms. Understanding the response of plants' molecular features to abiotic stress is a priority in the current period of continued environmental changes. Epigenetic modifications are necessary that control gene expression by changing chromatin status and recruiting various transcription regulators. The present study summarized the current knowledge on epigenetic modifications concerning plant responses to various environmental stressors. The functional relevance of epigenetic marks in regulating stress tolerance has been revealed, and epigenetic changes impact the effector genes. This study looks at the epigenetic mechanisms that govern plant abiotic stress responses, especially DNA methylation, histone methylation/acetylation, chromatin remodeling, and various metabolites. Plant breeders will benefit from a thorough understanding of these processes to create alternative crop improvement approaches. Genome editing with clustered regularly interspaced short palindromic repeat/CRISPR-associated proteins (CRISPR/Cas) provides genetic tools to make agricultural genetic engineering more sustainable and publicly acceptable.

Conservation and Diversity of miR166 Family Members From Highbush Blueberry (Vaccinium corymbosum) and Their Potential Functions in Abiotic Stress

MicroRNA166 (miR166) is highly conserved and has diverse functions across plant species. The highbush blueberry (Vaccinium corymbosum) genome is thought to harbor 10 miRNA166 loci (Vco-miR166), but the extent of their evolutionary conservation or functional diversification remains unknown. In this study, we identified six additional Vco-miR166 loci based on conserved features of the miR166 family. Phylogenetic analyses showed that mature Vco-miR166s and their precursor cluster in several clades are evolutionary conserved with diverse species. The cis-regulatory elements in the Vco-miR166 promoters indicated functions related to different phytohormones and defense responses. We also identified putative targets of vco-miR166s, which targeted the same gene families, suggesting the functional conservation and diversification of Vco-miR166 family members. Furthermore, we examined the accumulation patterns of six mature Vco-miR166s in response to abiotic stresses by stem-loop reverse RT-qPCR, which revealed their upregulation under freezing, cold, and heat stress, while they were downregulated by drought compared to control growth conditions. However, Vco-miR166 members showed different expression patterns when exposed to salt stress. These results showed that conserved Vco-miR166 family members display functional diversification but also coordinately influence plant responses to abiotic stress.

miRNA Profiling and Its Role in Multi-Omics Regulatory Networks Connected with Somaclonal Variation in Cucumber (Cucumis sativus L.)

The role of miRNAs in connection with the phenomenon of somaclonal variation, which occurs during plant in vitro culture, remains uncertain. This study aims to investigate the possible role of miRNAs in multi-omics regulatory pathways in cucumber somaclonal lines. For this purpose, we performed sRNA sequencing (sRNA-seq) from cucumber fruit samples identified 8, 10 and 44 miRNAs that are differentially expressed between somaclones (S1, S2, S3 lines) and the reference B10 line of Cucumis sativus. For miRNA identification, we use ShortStack software designed to filter miRNAs from sRNAs according to specific program criteria. The identification of predicted in-silico targets revealed 2,886 mRNAs encoded by 644 genes. The functional annotation of miRNA's target genes and gene ontology classification revealed their association with metabolic processes, response to stress, multicellular organism development, biosynthetic process and catalytic activity. We checked with bioinformatic analyses for possible interactions at the level of target proteins, differentially expressed genes (DEGs) and genes affected by genomic polymorphisms. We assume that miRNAs can indirectly influence molecular networks and play a role in many different regulatory pathways, leading to somaclonal variation. This regulation is supposed to occur through the process of the target gene cleavage or translation inhibition, which in turn affects the proteome, as we have shown in the example of molecular networks. This is a new approach combining levels from DNA-seq through mRNA-seq, sRNA-seq and in silico PPI in the area of plants' somaclonal variation.

Exploring the Effect of Methyl Jasmonate on the Expression of microRNAs Involved in Biosynthesis of Active Compounds of Rosemary Cell Suspension Cultures through RNA-Sequencing

Our aim in the experiment was to study the effects of methyl jasmonates (MeJA) on the active compounds of rosemary suspension cells, the metabolites' change of contents under different concentrations of MeJA, including 0 (CK), 10 (M10), 50 (M50) and 100 μM MeJA (M100). The results demonstrated that MeJA treatments promoted the accumulation of rosmarinic acid (RA), carnosic acid (CA), flavonoids, jasmonate (JA), gibberellin (GA), and auxin (IAA); but reduced the accumulations of abscisic acid (ABA), salicylic acid (SA), and aspartate (Asp). In addition, 50 and 100 μM MeJA promoted the accumulation of alanine (Ala) and glutamate (Glu), and 50 μM MeJA promoted the accumulation of linoleic acid and alpha-linolenic acid in rosemary suspension cells. Comparative RNA-sequencing analysis of different concentrations of MeJA showed that a total of 30, 61, and 39 miRNAs were differentially expressed in the comparisons of CKvsM10, CKvsM50, CKvsM100, respectively. The analysis of the target genes of the differentially expressed miRNAs showed that plant hormone signal transduction, linoleic acid, and alpha-linolenic acid metabolism-related genes were significantly enriched. In addition, we found that miR160a-5p target ARF, miR171d_1 and miR171f_3 target DELLA, miR171b-3p target ETR, and miR156a target BRI1, which played a key role in rosemary suspension cells under MeJA treatments. qRT-PCR of 12 differentially expressed miRNAs and their target genes showed a high correlation between the RNA-seq and the qRT-PCR result. Amplification culture of rosemary suspension cells in a 5 L stirred bioreactor showed that cell biomass accumulation in the bioreactor was less than that in the shake flask under the same conditions, and the whole cultivation period was extended to 14 d. Taken together, MeJA promoted the synthesis of the active compounds in rosemary suspension cells in a wide concentration range via concentration-dependent differential expression patterns. This study provided an overall view of the miRNAs responding to MeJA in rosemary.

Mechanisms of MicroRNA Biogenesis and Stability Control in Plants

MicroRNAs (miRNAs), a class of endogenous, non-coding RNAs, which is 20-24 nucleotide long, regulate the expression of its target genes post-transcriptionally and play critical roles in plant normal growth, development, and biotic and abiotic stresses. In cells, miRNA biogenesis and stability control are important in regulating intracellular miRNA abundance. In addition, research on these two aspects has achieved fruitful results. In this review, we focus on the recent research progress in our understanding of miRNA biogenesis and their stability control in plants.

Spatiotemporal expression profile of novel and known small RNAs throughout rice plant development focussing on seed tissues

Background

Small RNAs (sRNAs) regulate numerous plant processes directly related to yield, such as disease resistance and plant growth. To exploit this yield-regulating potential of sRNAs, the sRNA profile of one of the world’s most important staple crops – rice – was investigated throughout plant development using next-generation sequencing.

Results

Root and leaves were investigated at both the vegetative and generative phase, and early-life sRNA expression was characterized in the embryo and endosperm. This led to the identification of 49,505 novel sRNAs and 5581 tRNA-derived sRNAs (tsRNAs). In all tissues, 24 nt small interfering RNAs (siRNAs) were highly expressed and associated with euchromatic, but not heterochromatic transposable elements. Twenty-one nt siRNAs deriving from genic regions in the endosperm were exceptionally highly expressed, mimicking previously reported expression levels of 24 nt siRNAs in younger endosperm samples. In rice embryos, sRNA content was highly diverse while tsRNAs were underrepresented, possibly due to snoRNA activity. Publicly available mRNA expression and DNA methylation profiles were used to identify putative siRNA targets in embryo and endosperm. These include multiple genes related to the plant hormones gibberellic acid and ethylene, and to seed phytoalexin and iron content.

Conclusions

This work introduces multiple sRNAs as potential regulators of rice yield and quality, identifying them as possible targets for the continuous search to optimize rice production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08264-z.

Comparative Analysis of Coding and Non-Coding Features within Insect Tolerance Loci in Wheat with Their Homologs in Cereal Genomes

Food insecurity and malnutrition have reached critical levels with increased human population, climate fluctuations, water shortage; therefore, higher-yielding crops are in the spotlight of numerous studies. Abiotic factors affect the yield of staple food crops; among all, wheat stem sawfly (Cephus cinctus Norton) and orange wheat blossom midge (Sitodiplosis mosellana) are two of the most economically and agronomically harmful insect pests which cause yield loss in cereals, especially in wheat in North America. There is no effective strategy for suppressing this pest damage yet, and only the plants with intrinsic tolerance mechanisms such as solid stem phenotypes for WSS and antixenosis and/or antibiosis mechanisms for OWBM can limit damage. A major QTL and a causal gene for WSS resistance were previously identified in wheat, and 3 major QTLs and a causal gene for OWBM resistance. Here, we present a comparative analysis of coding and non-coding features of these loci of wheat across important cereal crops, barley, rye, oat, and rice. This research paves the way for our cloning and editing of additional WSS and OWBM tolerance gene(s), proteins, and metabolites.

Small RNA, Transcriptome and Degradome Analysis of the Transgenerational Heat Stress Response Network in Durum Wheat

Heat stress is a major limiting factor of grain yield and quality in crops. Abiotic stresses have a transgenerational impact and the mechanistic basis is associated with epigenetic regulation. The current study presents the first systematic analysis of the transgenerational effects of post-anthesis heat stress in tetraploid wheat. Leaf physiological traits, harvest components and grain quality traits were characterized under the impact of parental and progeny heat stress. The parental heat stress treatment had a positive influence on the offspring for traits including chlorophyll content, grain weight, grain number and grain total starch content. Integrated sequencing analysis of the small RNAome, mRNA transcriptome and degradome provided the first description of the molecular networks mediating heat stress adaptation under transgenerational influence. The expression profile of 1771 microRNAs (733 being novel) and 66,559 genes was provided, with differentially expressed microRNAs and genes characterized subject to the progeny treatment, parental treatment and tissue-type factors. Gene Ontology and KEGG pathway analysis of stress responsive microRNAs-mRNA modules provided further information on their functional roles in biological processes such as hormone homeostasis, signal transduction and protein stabilization. Our results provide new insights on the molecular basis of transgenerational heat stress adaptation, which can be used for improving thermo-tolerance in breeding.

Regulatory non-coding RNAs: a new frontier in regulation of plant biology

Beyond the most crucial roles of RNA molecules as a messenger, ribosomal, and transfer RNAs, the regulatory role of many non-coding RNAs (ncRNAs) in plant biology has been recognized. ncRNAs act as riboregulators by recognizing specific nucleic acid targets through homologous sequence interactions to regulate plant growth, development, and stress responses. Regulatory ncRNAs, ranging from small to long ncRNAs (lncRNAs), exert their control over a vast array of biological processes. Based on the mode of biogenesis and their function, ncRNAs evolved into different forms that include microRNAs (miRNAs), small interfering RNAs (siRNAs), miRNA variants (isomiRs), lncRNAs, circular RNAs (circRNAs), and derived ncRNAs. This article explains the different classes of ncRNAs and their role in plant development and stress responses. Furthermore, the applications of regulatory ncRNAs in crop improvement, targeting agriculturally important traits, have been discussed.

Nitrogen Starvation-Responsive MicroRNAs Are Affected by Transgenerational Stress in Durum Wheat Seedlings

Stress events have transgenerational effects on plant growth and development. In Mediterranean regions, water-deficit and heat (WH) stress is a frequent issue that negatively affects crop yield and quality. Nitrogen (N) is an essential plant macronutrient and often a yield-limiting factor for crops. Here, the response of durum wheat seedlings to N starvation under the transgenerational effects of WH stress was investigated in two genotypes. Both genotypes showed a significant reduction in seedling height, leaf number, shoot and root weight (fresh and dry), primary root length, and chlorophyll content under N starvation stress. However, in the WH stress-tolerant genotype, the percentage reduction of most traits was lower in progeny from the stressed parents than progeny from the control parents. Small RNA sequencing identified 1534 microRNAs in different treatment groups. Differentially expressed microRNAs (DEMs) were characterized subject to N starvation, parental stress and genotype factors, with their target genes identified in silico. GO and KEGG enrichment analyses revealed the biological functions, associated with DEM-target modules in stress adaptation processes, that could contribute to the phenotypic differences observed between the two genotypes. The study provides the first evidence of the transgenerational effects of WH stress on the N starvation response in durum wheat.

Small RNAs and their targets are associated with the transgenerational effects of water-deficit stress in durum wheat

Water-deficit stress negatively affects wheat yield and quality. Abiotic stress on parental plants during reproduction may have transgenerational effects on progeny. Here we investigated the transgenerational influence of pre-anthesis water-deficit stress by detailed analysis of the yield components, grain quality traits, and physiological traits in durum wheat. Next-generation sequencing analysis profiled the small RNA-omics, mRNA transcriptomics, and mRNA degradomics in first generation progeny. Parental water-deficit stress had positive impacts on the progeny for traits including harvest index and protein content in the less stress-tolerant variety. Small RNA-seq identified 1739 conserved and 774 novel microRNAs (miRNAs). Transcriptome-seq characterised the expression of 66,559 genes while degradome-seq profiled the miRNA-guided mRNA cleavage dynamics. Differentially expressed miRNAs and genes were identified, with significant regulatory patterns subject to trans- and inter-generational stress. Integrated analysis using three omics platforms revealed significant biological interactions between stress-responsive miRNA and targets, with transgenerational stress tolerance potentially contributed via pathways such as hormone signalling and nutrient metabolism. Our study provides the first confirmation of the transgenerational effects of water-deficit stress in durum wheat. New insights gained at the molecular level indicate that key miRNA-mRNA modules are candidates for transgenerational stress improvement.

Genome-Wide Identification of Copper Stress-Regulated and Novel MicroRNAs in Mulberry Leaf

Copper (Cu) is an essential trace element for plant growth and development. It is widely involved in respiration, photosynthesis, pollen formation, and other biological processes. Therefore, low or excessive copper causes damage to plants. Mulberry is an essential perennial economic tree. At present, research on the abiotic stress responses in mulberry is mainly focused on the identification of resistant germplasm resources and cloning of resistant genes. In contrast, studies on the resistance function of microRNAs and the regulatory gene responses to stress are rare. In this study, small RNA libraries (control and copper stressed) were constructed from mulberry leaf RNA. High-throughput sequencing and screening were employed, a total of 65 known miRNAs and 78 predicted novel mature miRNAs were identified, among which 40 miRNAs were differentially expressed under copper stress. Subsequently, expression patterns were verified for 14 miRNAs by real-time fluorescence quantitative PCR (qPCR). The target genes of miRNAs were validated by 5' RLM-RACE. Our results provide the bases for further study on the molecular mechanism of copper stress regulation in mulberry.

Domestication of High-Copy Transposons Underlays the Wheat Small RNA Response to an Obligate Pathogen

Plant genomes have evolved several evolutionary mechanisms to tolerate and make use of transposable elements (TEs). Of these, transposon domestication into cis-regulatory and microRNA (miRNA) sequences is proposed to contribute to abiotic/biotic stress adaptation in plants. The wheat genome is derived at 85% from TEs, and contains thousands of miniature inverted-repeat transposable elements (MITEs), whose sequences are particularly prone for domestication into miRNA precursors. In this study, we investigate the contribution of TEs to the wheat small RNA immune response to the lineage-specific, obligate powdery mildew pathogen. We show that MITEs of the Mariner superfamily contribute the largest diversity of miRNAs to the wheat immune response. In particular, MITE precursors of miRNAs are wide-spread over the wheat genome, and highly conserved copies are found in the Lr34 and QPm.tut-4A mildew resistance loci. Our work suggests that transposon domestication is an important evolutionary force driving miRNA functional innovation in wheat immunity.

Integrated Analysis of Small RNA, Transcriptome, and Degradome Sequencing Reveals the Water-Deficit and Heat Stress Response Network in Durum Wheat

Water-deficit and heat stress negatively impact crop production. Mechanisms underlying the response of durum wheat to such stresses are not well understood. With the new durum wheat genome assembly, we conducted the first multi-omics analysis with next-generation sequencing, providing a comprehensive description of the durum wheat small RNAome (sRNAome), mRNA transcriptome, and degradome. Single and combined water-deficit and heat stress were applied to stress-tolerant and -sensitive Australian genotypes to study their response at multiple time-points during reproduction. Analysis of 120 sRNA libraries identified 523 microRNAs (miRNAs), of which 55 were novel. Differentially expressed miRNAs (DEMs) were identified that had significantly altered expression subject to stress type, genotype, and time-point. Transcriptome sequencing identified 49,436 genes, with differentially expressed genes (DEGs) linked to processes associated with hormone homeostasis, photosynthesis, and signaling. With the first durum wheat degradome report, over 100,000 transcript target sites were characterized, and new miRNA-mRNA regulatory pairs were discovered. Integrated omics analysis identified key miRNA-mRNA modules (particularly, novel pairs of miRNAs and transcription factors) with antagonistic regulatory patterns subject to different stresses. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis revealed significant roles in plant growth and stress adaptation. Our research provides novel and fundamental knowledge, at the whole-genome level, for transcriptional and post-transcriptional stress regulation in durum wheat.

Biotic stress triggered small RNA and RNAi defense response in plants

The yield of crops is largely affected by different types of biotic stresses. To minimize the damage, crop plants adapted themselves to overcome the stress conditions through gene expression reprogramming at transcriptional and post-transcriptional levels. With a better knowledge of plants' responses in adverse environments, new methodologies and strategies have been applied to develop better stress-tolerant plants. In this manner, small RNAs (micro RNA and small-interfering RNA) are reported to play a central role to combat biotic stresses in plants. Depending upon the stress stimuli, these small RNAs can up or down regulate the genes expression, that indicate their potential role in overcoming the stress. These stress-induced small RNAs may reduce the expression of the target gene(s) that might negatively influence plants' response to the adverse conditions. Contrariwise, miRNA, a class of small RNA, can downregulate its expression to upregulate the expression of the target gene(s), which might positively aid to the stress adaptation. Along with this, benefits of RNA interference (RNAi) have also been stated in functional genomic research on insects, fungi and plant pathogens. RNAi is involved in the safe transport of dsRNA to the targeted mRNA(s) in the biotic stress-causing agents (for example fungi and insects) and saves the plant from damage, which is a safer approach compared to use of chemical pesticides. The current review summarizes the role of small RNAs and the use of RNAi to save the plants from biotic stress conditions.

Biotechnological Perspectives of Omics and Genetic Engineering Methods in Alfalfa

For several decades, researchers are working to develop improved major crops with better adaptability and tolerance to environmental stresses. Forage legumes have been widely spread in the world due to their great ecological and economic values. Abiotic and biotic stresses are main factors limiting legume production, however, alfalfa (Medicago sativa L.) shows relatively high level of tolerance to drought and salt stress. Efforts focused on alfalfa improvements have led to the release of cultivars with new traits of agronomic importance such as high yield, better stress tolerance or forage quality. Alfalfa has very high nutritional value due to its efficient symbiotic association with nitrogen-fixing bacteria, while deep root system can help to prevent soil water loss in dry lands. The use of modern biotechnology tools is challenging in alfalfa since full genome, unlike to its close relative barrel medic (Medicago truncatula Gaertn.), was not released yet. Identification, isolation, and improvement of genes involved in abiotic or biotic stress response significantly contributed to the progress of our understanding how crop plants cope with these environmental challenges. In this review, we provide an overview of the progress that has been made in high-throughput sequencing, characterization of genes for abiotic or biotic stress tolerance, gene editing, as well as proteomic and metabolomics techniques bearing biotechnological potential for alfalfa improvement.

LncRNA improves cold resistance of winter wheat by interacting with miR398

One of the important functions of long non-coding RNA (lncRNA) is to be competing endogenous RNAs (ceRNAs). As miR398 is reported to respond to different stressors, it is necessary to explore its relationship with lncRNA in the cold resistance mechanism of winter wheat. Tae-miR398-precursor sequence was isolated from the winter wheat (Triticum aestivum). RLM-RACE verified that tae-miR398 cleaved its target CSD1. Quantitative detection at 5°C, -10°C and -25°C showed that the expression of tae-miR398 decreased in response to low temperatures, whereas CSD1 showed an opposite expression pattern. LncR9A, lncR117 and lncR616 were predicted and verified to interact with miR398. tae-miR398 and three lncRNAs were transferred into Arabidopsis thaliana respectively. The lncR9A were transferred into Brachypodium distachyom. Transgenic plants were cultivated at -8°C and assessed for the expression of malondialdehyde, chlorophyll, superoxide dismutase and miR398-lncRNA-target mRNA. The results demonstrate that tae-miR398 regulates low temperature tolerance by downregulating its target, CSD1. lncRNA regulates the expression of CSD1 indirectly by competitively binding miR398, which, in turn, affects the resistance of Dn1 to cold. miR398-regulation triggers a regulatory loop that is critical to cold stress tolerance in wheat. Our findings offer an improved strategy to crop plants with enhanced stress tolerance.

Machine learning improves our knowledge about miRNA functions towards plant abiotic stresses

During the last two decades, human has increased his knowledge about the role of miRNAs and their target genes in plant stress response. Biotic and abiotic stresses result in simultaneous tissue-specific up/down-regulation of several miRNAs. In this study, for the first time, feature selection algorithms have been used to investigate the contribution of individual plant miRNAs in Arabidopsis thaliana response towards different levels of several abiotic stresses including drought, salinity, cold, and heat. Results of information theory-based feature selection revealed that miRNA-169, miRNA-159, miRNA-396, and miRNA-393 had the highest contributions to plant response towards drought, salinity, cold, and heat, respectively. Furthermore, regression models, i.e., decision tree (DT), support vector machines (SVMs), and Naïve Bayes (NB) were used to predict the plant stress by having the plant miRNAs' concentration. SVM with Gaussian kernel was capable of predicting plant stress (R2 = 0.96) considering miRNA concentrations as input features. Findings of this study prove the performance of machine learning as a promising tool to investigate some aspects of miRNAs' contribution to plant stress responses that have been undiscovered until today.

Different MicroRNA Families Involved in Regulating High Temperature Stress Response during Cotton (Gossypium hirsutum L.) Anther Development

MicroRNAs (miRNAs) are small molecule RNAs widely involved in responses to plant abiotic stresses. We performed small RNA sequencing of cotton anthers at four developmental stages under normal and high temperature (NT and HT, respectively) conditions to investigate the stress response characteristics of miRNA to HT. A total of 77 miRNAs, including 33 known miRNAs and 44 novel miRNAs, were identified, and 41 and 28 miRNAs were differentially expressed under NT and HT stress conditions, respectively. The sporogenous cell proliferation (SCP), meiotic phase (MP), microspore release period (MRP), and pollen maturity (PM) stages had 10 (including 12 miRNAs), four (including six miRNAs), four (including five miRNAs), and seven (including 11 miRNAs) HT stress-responsive miRNA families, respectively, which were identified after removing the changes in genotype-specific miRNAs under NT condition. Seven miRNA families (miR2949, miR167, and miR160 at the SCP stage; miR156 and miR172 at the MP stage; miR156 at the MRP stage; and miR393 and miR3476 at the PM stage), which had expression abundance of more than 10% of the total expression abundance, served as the main regulators responding to HT stress with positive or negative regulation patterns. These miRNAs orchestrated the expression of the corresponding target genes and led to different responses in the HT-tolerant and the HT-sensitive lines. The results revealed that the HT stress response of miRNAs in cotton anthers were stage-specific and differed with the development of anthers. Our study may enhance the understanding of the response of miRNAs to HT stress in cotton anthers and may clarify the mechanism of plant tolerance to HT stress.

Transgenerational Effects of Water-Deficit and Heat Stress on Germination and Seedling Vigour-New Insights from Durum Wheat microRNAs

Water deficiency and heat stress can severely limit crop production and quality. Stress imposed on the parents during reproduction could have transgenerational effects on their progeny. Seeds with different origins can vary significantly in their germination and early growth. Here, we investigated how water-deficit and heat stress on parental durum wheat plants affected seedling establishment of the subsequent generation. One stress-tolerant and one stress-sensitive Australian durum genotype were used. Seeds were collected from parents with or without exposure to stress during reproduction. Generally, stress on the previous generation negatively affected seed germination and seedling vigour, but to a lesser extent in the tolerant variety. Small RNA sequencing utilising the new durum genome assembly revealed significant differences in microRNA (miRNA) expression in the two genotypes. A bioinformatics approach was used to identify multiple miRNA targets which have critical molecular functions in stress adaptation and plant development and could therefore contribute to the phenotypic differences observed. Our data provide the first confirmation of the transgenerational effects of reproductive-stage stress on germination and seedling establishment in durum wheat. New insights gained on the epigenetic level indicate that durum miRNAs could be key factors in optimising seed vigour for breeding superior germplasm and/or varieties.

Development and Characterization of Near-Isogenic Lines Revealing Candidate Genes for a Major 7AL QTL Responsible for Heat Tolerance in Wheat

Wheat is one of the most important food crops in the world, but as a cool-season crop, it is more prone to heat stress, which severely affects crop production and grain quality. Heat tolerance in wheat is a quantitative trait, and the genes underlying reported quantitative trait loci (QTL) have rarely been identified. Near-isogenic lines (NILs) with a common genetic background but differing at a particular locus could turn quantitative traits into a Mendelian factor; therefore, they are suitable material for identifying candidate genes for targeted locus/loci. In this study, we developed and characterized NILs from two populations Cascades × Tevere and Cascades × W156 targeting a major 7AL QTL responsible for heat tolerance. Molecular marker screening and phenotyping for SPAD chlorophyll content and grain-yield-related traits confirmed four pairs of wheat NILs that contrasted for heat-stress responses. Genotyping the NILs using a 90K Infinium iSelect SNP array revealed five single nucleotide polymorphism (SNP) markers within the QTL interval that were distinguishable between the isolines. Seven candidate genes linked to the SNPs were identified as related to heat tolerance, and involved in important processes and pathways in response to heat stress. The confirmed multiple pairs of NILs and identified candidate genes in this study are valuable resources and information for further fine-mapping to clone major genes for heat tolerance.

Plant microRNAs: biogenesis, gene silencing, web-based analysis tools and their use as molecular markers

MicroRNAs (miRNAs) are tiny (20-24 nt bp) regulatory non-protein-coding RNA molecules that have been extensively characterized and found important for many physiological and developmental processes. The miss-expression of miRNAs leads to various defects in plants. MicroRNAs repress gene expression by directing mRNA degradation or translational arrest. Several proteins such as PP43A, HYL1, DCL, HST are indispensable role players in promoting miRNA biogenesis in plants. During miRNA biogenesis, lariat RNAs are produced as by-products of pre-mRNA splicing which have a negative role in regulation of miRNA homeostasis. By acting as a decoy and by sequestering to the dicing complex, lariat RNA can prevent the processing of miRNAs. A number of bioinformatic tools with different methodologies are available to identify and validate miRNAs and their targets. Many miRNAs have been reported in different crops for different traits; however, no reports are available on their use in plant breeding. Recently, researchers have developed trait specific miRNA-based molecular markers (miRNA-SSRs/SNP) for many quantitative traits in different plant species. In the future, these molecular markers can be used for plant breeding programs. In this review, a comprehensive up-to-date information is provided on the bioinformatic tools used for analysis of plant miRNAs and their targets, the number of miRNAs, their biogenesis, gene silencing mechanism and miRNA-based molecular markers.

Water-deficit responsive microRNAs in the primary root growth zone of maize

BACKGROUND

MicroRNA-mediated gene regulatory networks play a significant role in plant growth and development and environmental stress responses.

RESULTS

We identified 79 microRNAs (miRNAs) and multiple miRNA variants (isomiRs) belonging to 26 miRNA families in the primary root growth zone of maize seedlings grown at one of three water potentials: well-watered (- 0.02 MPa), mild water deficit stress (- 0.3 MPa), and severe water deficit stress (- 1.6 MPa). The abundances of 3 miRNAs (mild stress) and 34 miRNAs representing 17 families (severe stress) were significantly different in water-deficit stressed relative to well-watered controls (FDR < 0.05 and validated by stem loop RT-qPCR). Degradome sequencing revealed 213 miRNA-regulated transcripts and trancriptome profiling revealed that the abundance of 77 (miRNA-regulated) were regulated by water-defecit stress. miR399e,i,j-3p was strongly regulated by water-defcit stress implicating the possibility of nutrient deficiency during stress.

CONCLUSIONS

We have identified a number of maize miRNAs that respond to specific water deficits applied to the primary root growth zone. We have also identified transcripts that are targets for miRNA regulation in the root growth zone under water-deficit stress. The miR399e,i,j-3p that is known to regulate phosphate uptake in response to nutrient deficiencies responds to water-deficit stress, however, at the seedling stage the seed provides adequate nutrients for root growth thus miR399e,i,j-3p may play a separate role in water-deficit responses. A water-deficit regulated maize transcript, similar to known miR399 target mimics, was identified and we hypothesized that it is another regulatory player, moderating the role of miR399e,i,j-3p, in primary root growth zone water deficit responses.

Genotypic performance of Australian durum under single and combined water-deficit and heat stress during reproduction

In Mediterranean environments, water deficiency and heat during reproduction severely limit cereal crop production. Our research investigated the effects of single and combined pre-anthesis water-deficit stress and post-anthesis heat stress in ten Australian durum genotypes, providing a systematic evaluation of stress response at the molecular, physiological, grain quality and yield level. We studied leaf physiological traits at different reproductive stages, evaluated the grain yield and quality, and the associations among them. We profiled the expression dynamics of two durum microRNAs and their protein-coding targets (auxin response factors and heat shock proteins) involved in stress adaptation. Chlorophyll content, stomatal conductance and leaf relative water content were mostly reduced under stress, however, subject to the time-point and genotype. The influence of stress on grain traits (e.g., protein content) also varied considerably among the genotypes. Significant positive correlations between the physiological traits and the yield components could be used to develop screening strategies for stress improvement in breeding. Different expression patterns of stress-responsive microRNAs and their targets in the most stress-tolerant and most stress-sensitive genotype provided some insight into the complex defense molecular networks in durum. Overall, genotypic performance observed indicates that different stress-coping strategies are deployed by varieties under various stresses.

RNAseq analysis reveals drought-responsive molecular pathways with candidate genes and putative molecular markers in root tissue of wheat

Drought is one of the major impediments in wheat productivity. Traditional breeding and marker assisted QTL introgression had limited success. Available wheat genomic and RNA-seq data can decipher novel drought tolerance mechanisms with putative candidate gene and marker discovery. Drought is first sensed by root tissue but limited information is available about how roots respond to drought stress. In this view, two contrasting genotypes, namely, NI5439 41 (drought tolerant) and WL711 (drought susceptible) were used to generate ~78.2 GB data for the responses of wheat roots to drought. A total of 45139 DEGs, 13820 TF, 288 miRNAs, 640 pathways and 435829 putative markers were obtained. Study reveals use of such data in QTL to QTN refinement by analysis on two model drought-responsive QTLs on chromosome 3B in wheat roots possessing 18 differentially regulated genes with 190 sequence variants (173 SNPs and 17 InDels). Gene regulatory networks showed 69 hub-genes integrating ABA dependent and independent pathways controlling sensing of drought, root growth, uptake regulation, purine metabolism, thiamine metabolism and antibiotics pathways, stomatal closure and senescence. Eleven SSR markers were validated in a panel of 18 diverse wheat varieties. For effective future use of findings, web genomic resources were developed. We report RNA-Seq approach on wheat roots describing the drought response mechanisms under field drought conditions along with genomic resources, warranted in endeavour of wheat productivity.

Small RNA Mobility: Spread of RNA Silencing Effectors and its Effect on Developmental Processes and Stress Adaptation in Plants

Plants are exposed every day to multiple environmental cues, and tight transcriptome reprogramming is necessary to control the balance between responses to stress and processes of plant growth. In this context, the silencing phenomena mediated by small RNAs can drive transcriptional and epigenetic regulatory modifications, in turn shaping plant development and adaptation to the surrounding environment. Mounting experimental evidence has recently pointed to small noncoding RNAs as fundamental players in molecular signalling cascades activated upon exposure to abiotic and biotic stresses. Although, in the last decade, studies on stress responsive small RNAs increased significantly in many plant species, the physiological responses triggered by these molecules in the presence of environmental stresses need to be further explored. It is noteworthy that small RNAs can move either cell-to-cell or systemically, thus acting as mobile silencing effectors within the plant. This aspect has great importance when physiological changes, as well as epigenetic regulatory marks, are inspected in light of plant environmental adaptation. In this review, we provide an overview of the categories of mobile small RNAs in plants, particularly focusing on the biological implications of non-cell autonomous RNA silencing in the stress adaptive response and epigenetic modifications.

Comparative profiling of roots small RNA expression and corresponding gene ontology and pathway analyses for low- and high-cadmium-accumulating genotypes of wheat in response to cadmium stress

MicroRNAs (miRNAs) participate in multiple biological processes in plant. Cd accumulation ability differs among varieties in wheat, but little is known about miRNAs and their function in Cd accumulation of wheat under Cd stress. Therefore, the present study detected small RNAs responsible for differential Cd accumulation between two contrasting wheat genotypes (low-Cd accumulation one L17 and high-Cd accumulation one H17) to identify novel targets to further study Cd stress in wheat. Under normal conditions, 139 miRNAs were differentially expressed between L17 and H17, while this value reached 142 after Cd exposure. For Cd-induced DEMs, total 25 miRNAs were differentially expressed in L17 after Cd treatment, while, 70 Cd-induced DEMs were found in H17. Moreover, GO analysis revealed that target genes of DEMs related to lipid biosynthetic process and chlorophyll binding are uniquely enriched in L17, target genes of DEMs related to ribosome biogenesis and sucrose alpha-glucosidase activity are uniquely enriched in H17. By pathway analysis, target genes of DEMs related to PI3K-Akt signaling pathway was specifically enriched in L17, target genes of DEMs related to carbohydrate digestion and absorption pathway was uniquely enriched in H17. In addition, miRNA-gene co-expression showed that tae-miR9774 was uniquely expressed between L17Cd and L17CK, while tae-miR398 was specially expressed between H17Cd and H17CK. Our results suggested that Cd-accumulating ability of L17 and H17 varied from the expression of induced unique miRNA, such as expression of tae-miR-9774 and tae-miR-398. Our study not only provide the foundation for further exploring the miRNAs-induced molecular mechanisms of Cd accumulation in wheat but also supply novel strategies for improving phytoremediation ability of food plants through genetic engineering.

MicroRNA-154 Targets the Wnt/β-Catenin Signaling Pathway Following Injury to Human Vascular Endothelial Cells by Hydrogen Peroxide

Background

Endothelial cells are involved in vascular homeostasis, and endothelial cell dysfunction is involved in the pathogenesis of cardiovascular disease. This study aimed to investigate the effects of microRNA-154 in human umbilical vein endothelial cells (HUVECs) following injury induced by hydrogen peroxide (H₂O₂).

Material/Methods

Cell viability and apoptosis of HUVECs treated with H₂O₂ were measured. The expression of microRNA-154 was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Cell survival, caspase-3 activity, and the apoptosis rate were evaluated in H₂O₂-treated HUVECs cells after the upregulation and down-regulation of microRNA-154 expression. The interaction between microRNA-154 and Dickkopf WNT signaling pathway inhibitor 2 (DKK2) was predicted by bioinformatics analysis and was verified by luciferase reporter gene assay and Western blot. The effects of DKK2 short-interfering RNA (siRNA) on antioxidant injury in HUVECs cells were determined.

Results

The survival rate of HUVECs exposed to H₂O₂ was significantly reduced and the apoptosis rate was significantly increased, and H₂O₂ significantly inhibited the expression of microRNA-154 in a dose-dependent manner. Overexpression of microRNA-154 increased cell survival, reduced the activity of caspase-3, and reduced cell apoptosis. Inhibition of microRNA-154 expression decreased cell survival, increased the activity of caspase-3, and promoted cell apoptosis. Luciferase reporter gene assay and Western blot showed that microRNA-154 interacted with the Wnt pathway molecule DKK2 in HUVECS. Also, DDK2 siRNA resulted in a similar protective effect on H₂O₂-treated HUVECs as overexpression of microRNA-154.

Conclusions

Oxidative injury in HUVECs was regulated by microRNA-154 targeting the Wnt/β-catenin signaling pathway.

Identification of Fusarium graminearum-responsive miRNAs and their targets in wheat by sRNA sequencing and degradome analysis

Fusarium head blight (FHB), a prevalent disease of bread wheat (Triticum aestivum L.) caused by Fusarium graminearum, leads to considerable losses of yield and quality in wheat production. MicroRNAs (miRNAs) are important regulators of plant defense responses. Here, to better understand the F. graminearum-responsive miRNAs, we constructed sRNA libraries for wheat cultivar Sumai 3 challenged with F. graminearum and sterile water, respectively. As a result, a total of 203 known miRNAs from 46 families and 68 novel miRNAs were identified. Among them, 18 known and six novel miRNAs were found to be differentially expressed between the F. graminearum-infected samples and the controls and thus were considered to be responsive to F. graminearum. The expression patterns of eight miRNAs were further validated by stem-loop qRT-PCR. Meanwhile, target genes were validated by degradome sequencing. Integrative analysis of the differentially expressed miRNAs and their targets revealed complex miRNA-mediated regulatory networks involved in the response of wheat to F. graminearum infection. Our findings are expected to facilitate a better understanding of the miRNA regulation in wheat-F. graminearum interaction.

Lineage-Specific Evolved MicroRNAs Regulating NB-LRR Defense Genes in Triticeae

Disease resistance genes encoding proteins with nucleotide binding sites and Leucine-Rich Repeat (NB-LRR) domains include many members involved in the effector-triggered immunity pathway in plants. The transcript levels of these defense genes are negatively regulated by diverse microRNAs (miRNAs) in angiosperms and gymnosperms. In wheat, using small RNA expression datasets and degradome datasets, we identified five miRNA families targeting NB-LRR defense genes in monocots, some of which arose in the Triticeae species era. These miRNAs regulate different types of NB-LRR genes, most of them with coil-coiled domains, and trigger the generation of secondary small interfering RNAs (siRNA) as a phased pattern in the target site regions. In addition to acting in response to biotic stresses, they are also responsive to abiotic stresses such as heat, drought, salt, and light stress. Their copy number and expression variation in Triticeae suggest a rapid birth and death frequency. Altogether, non-conserved miRNAs as conserved transcriptional regulators in gymnosperms and angiosperms regulating the disease resistance genes displayed quick plasticity including the variations of sequences, gene copy number, functions, and expression level, which accompanied with NB-LRR genes may be tune-regulated to plants in natural environments with various biotic and abiotic stresses.

Identification of microRNA-target modules from rice variety Pusa Basmati-1 under high temperature and salt stress

High temperature and salinity stress are major factors limiting the growth and productivity of rice crop on a global scale. It is therefore an essential prerequisite to understand the molecular genetic regulation of plant responses to dual stresses. MicroRNAs (miRs) are recognized as key controllers of gene expression which act mainly at the post-transcriptional level to regulate various aspects of plant development. The present study attempts to investigate the miR circuits that are modulated in response to high temperature and salinity stress in rice. To gain insights into the pathway, preliminary miR profiles were generated using the next-generation sequencing (NGS) datasets. The identified molecules were filtered on the basis of fold differential regulation under high temperature, and time kinetics of their expression under the two individual stresses was followed to capture the regulatory windows. The analysis revealed the involvement of common miR regulatory nodes in response to two different abiotic stresses, thereby broadening our perspective about the stress-mediated regulatory mechanisms operative in rice.

Stress-responsive miRNAome of Glycine max (L.) Merrill: molecular insights and way forward

MAIN CONCLUSION

Analysis of stress-associated miRNAs of Glycine max (L.) Merrill reveals wider ramifications of small RNA-mediated (conserved and legume-specific miRNAs) gene regulatory foot prints in molecular adaptive responses. MicroRNAs (miRNAs) are indispensable components of gene regulatory mechanism of plants. Soybean is a crop of immense commercial potential grown worldwide for its edible oil and soy meal. Intensive research efforts, using the next generation sequencing and bioinformatics techniques, have led to the identification and characterization of numerous small RNAs, especially microRNAs (miRNAs), in soybean. Furthermore, studies have unequivocally demonstrated the significance of miRNAs during the developmental processes and various stresses in soybean. In this review, we summarize the current state of understanding of miRNA-based abiotic and biotic stress responses in soybean. In addition, the molecular insights gained from the stress-related soybean miRNAs have been compared to the miRNAs of other crops, especially legumes, and the core commonalities have been highlighted, though differences among them were not ignored. Nature of response of soybean-derived conserved miRNAs during various stresses was also analyzed to gain deeper insights regarding sRNAome-based defense responses. This review further provides way forward in legume small RNA transcriptomics based on the adaptive responses of soybean and other legume-derived miRNAs.

Plant microRNAs: Biogenesis, Homeostasis, and Degradation

MicroRNAs (miRNAs), a class of endogenous, tiny, non-coding RNAs, are master regulators of gene expression among most eukaryotes. Intracellular miRNA abundance is regulated under multiple levels of control including transcription, processing, RNA modification, RNA-induced silencing complex (RISC) assembly, miRNA-target interaction, and turnover. In this review, we summarize our current understanding of the molecular components and mechanisms that influence miRNA biogenesis, homeostasis, and degradation in plants. We also make comparisons with findings from other organisms where necessary.

Salinity-associated microRNAs and their potential roles in mediating salt tolerance in rice colonized by the endophytic root fungus Piriformospora indica

Piriformospora indica (P. indica), an endophytic root fungus, supports the growth and enhanced tolerance of plants to biotic and abiotic stresses. Several recent studies showed the significant role of small RNA (sRNA) molecules including microRNAs (miRNAs) in plant adaption to environmental stress, but little is known concerning the symbiosis-mediated salt stress tolerance regulated at miRNAs level. The overarching goal of this research is to elucidate the impact of miRNAs in regulating the P. indica-mediated salt tolerance in rice. Applying sRNA-seq analysis led to identify a set of 547 differentially abundant miRNAs in response to P. indica inoculation and salt stress. These included 206 rice-specific and 341 previously known miRNAs from other plant species. In silico analysis of miRNAs predictions of the differentially abundant miRNAs led to identifying of 193 putatively target genes, most of which were encoded either genes or transcription factors involved in nutrient uptake, sodium ion transporters, growth regulators, and auxin- responsive proteins. The rice-specific miRNAs targeted the transcription factors involved in the import of potassium ions into the root cells, the export of sodium ions, and plant growth and development. Interestingly, P. indica affected the differential abundance of miRNAs regulated genes and transcription factors linked to salt stress tolerance. Our data helps to understand the molecular basis of salt stress tolerance mediated by symbionts in plant and the potential impact of miRNAs for genetic improvement of rice varieties for tolerance to salt stress.

MicroRNAome Profile of Euphorbia kansui in Response to Methyl Jasmonate

miRNAs play vital regulatory roles in different plant developmental stages and in plant response to biotic and abiotic stresses. However, information is limited on the miRNA regulatory mechanism to methyl jasmonate (MeJA). In this study, we used the microRNAome profile to illustrate the relevant regulatory mechanisms of Euphorbia kansui in response to methyl jasmonate (MeJA) through Illumina RNA-Seq. As a result, we identified 875 miRNAs corresponding to 11,277 target mRNAs, among them, 168 known miRNA families representing 6019 target mRNAs sequences were obtained. 452 miRNA-mRNA pairs presented an anti-correlationship (Cor < −0.50 and p-value of correlation ≤ 0.05). The miRNA with a fold change ≥ 2 and a p (p-Value) < 0.05 in pairwise comparison were identified as significant differentially expressed miRNAs (DEMs). The DEMs in MeJA treatment of 0, 24, 36 and 48 h were compared by using Short Time Expression Miner (STEM) cluster and 4 significant gene profiles (p-value ≤ 0.02) were identified. Through the kyoto encyclopedia of genes and genomes (KEGG) pathway and gene ontology (GO) enrichment analysis on all miRNA targets, we identified 33 mRNAs in terpenoid biosynthesis, which were regulated by miRNAs under MeJA treatment, so the miRNA maybe involved in the response of E. kansui plant to exogenous MeJA and the results would provide very useful information on illustrating the regulatory mechanism of E. kansui and also provide an overall view of the miRNAs response to MeJA stress of a non-model plant.

Exploring miRNAs for developing climate-resilient crops: A perspective review

Climate changes and environmental stresses have significant implications on global crop production and necessitate developing crops that can withstand an array of climate changes and environmental perturbations such as irregular water-supplies leading to drought or water-logging, hyper soil-salinity, extreme and variable temperatures, ultraviolet radiations and metal stress. Plants have intricate molecular mechanisms to cope with these dynamic environmental changes, one of the most common and effective being the reprogramming of expression of stress-responsive genes. Plant microRNAs (miRNAs) have emerged as key post-transcriptional and translational regulators of gene-expression for modulation of stress implications. Recent reports are establishing their key roles in epigenetic regulations of stress/adaptive responses as well as in providing plants genome-stability. Several stress responsive miRNAs are being identified from different crop plants and miRNA-driven RNA-interference (RNAi) is turning into a technology of choice for improving crop traits and providing phenotypic plasticity in challenging environments. Here we presents a perspective review on exploration of miRNAs as potent targets for engineering crops that can withstand multi-stress environments via loss-/gain-of-function approaches. This review also shed a light on potential roles plant miRNAs play in genome-stability and their emergence as potent target for genome-editing. Current knowledge on plant miRNAs, their biogenesis, function, their targets, and latest developments in bioinformatics approaches for plant miRNAs are discussed. Though there are recent reviews discussing primarily the individual miRNAs responsive to single stress factors, however, considering practical limitation of this approach, special emphasis is given in this review on miRNAs involved in responses and adaptation of plants to multi-stress environments including at epigenetic and/or epigenomic levels.

High-throughput sequencing and differential expression analysis of miRNAs in response to Brassinosteroid treatment in Arabidopsis thaliana

Brassinosteroids are a class of phytohormones that play crucial roles in improving stress tolerance in plants. Many biochemical and physiological changes in response to abiotic stress are related to regulation of gene expression and accumulation of associated proteins. MicroRNAs (miRNAs) are class of small non-coding RNAs that regulate gene expression post-transcriptionally. Roles of these regulatory RNAs in brassinosteroid (BR) signalling have however remained elusive. In this study using high-throughput small RNA sequencing method, we present a comprehensive compilation of BR-induced differentially expressed microRNAs in root and shoots of Arabidopsis thaliana seedlings. We identified 229 known miRNAs belonging to 102 families and 27 novel miRNAs that express in response to exogenous BR treatment. Out of 102 families, miRNAs belonging to known 48 families and out of 27 novel miRNAs, 23 were observed to be differentially expressed in response to BR treatment. Among the conserved miRNAs, all members of miR169 were observed to be downregulated in both shoot and root samples. While, auxin-responsive factors were predicted to be direct targets of some novel miRNAs that are upregulated in shoots and suppressed in roots. The BR-responsive tissue-specific miRNome characterized in this study can be used as a starting point by investigators for functional validation studies that will shed light on the underlying molecular mechanism of BR-mediated stress tolerance at the level of post-transcriptional gene regulation.

Evolution of Disease Defense Genes and Their Regulators in Plants

Biotic stresses do damage to the growth and development of plants, and yield losses for some crops. Confronted with microbial infections, plants have evolved multiple defense mechanisms, which play important roles in the never-ending molecular arms race of plant–pathogen interactions. The complicated defense systems include pathogen-associated molecular patterns (PAMP) triggered immunity (PTI), effector triggered immunity (ETI), and the exosome-mediated cross-kingdom RNA interference (CKRI) system. Furthermore, plants have evolved a classical regulation system mediated by miRNAs to regulate these defense genes. Most of the genes/small RNAs or their regulators that involve in the defense pathways can have very rapid evolutionary rates in the longitudinal and horizontal co-evolution with pathogens. According to these internal defense mechanisms, some strategies such as molecular switch for the disease resistance genes, host-induced gene silencing (HIGS), and the new generation of RNA-based fungicides, have been developed to control multiple plant diseases. These broadly applicable new strategies by transgene or spraying ds/sRNA may lead to reduced application of pesticides and improved crop yield.

MicroR408 regulates defense response upon wounding in sweet potato

MiRNAs play diverse roles in plant development and defense responses by binding to their mRNA targets based on sequence complementarity. Here, we investigated a wound-related miR408 and its target genes in sweet potato (Ipomoea batatas) by small RNA deep sequencing and transcriptome analysis. The expression patterns of miR408 and the miR408 precursor were significantly repressed by wounding and jasmonate (JA). In contrast, expression of the putative target genes IbKCS (3-ketoacyl-CoA synthase 4), IbPCL (plantacyanin), and IbGAUT (galacturonosyltransferase 7-like) of miR408 was increased following wounding, whereas only IbKCS was increased after JA treatment. Target cleavage site mapping and Agrobacterium-mediated transient assay demonstrated that IbKCS, IbPCL, and IbGAUT were the targets of miR408. The expression of miR408 target genes was repressed in transgenic sweet potatoes overexpressing miR408. These data indicated a relationship between miR408 and its target genes. Notably, miR408-overexpressing plants showed a semi-dwarf phenotype and attenuated resistance to insect feeding, while transgenic plants overexpressing IbKCS exhibited more insect resistance than plants overexpressing only the empty vector. Collectively, sweet potato reduces the abundance of miR408 upon wounding to elevate the expression of IbKCS, IbPCL, and IbGAUT. The expression of IbKCS enhances the defense system against herbivore wounding.