SMARTER De-Stressed Cereal Breeding

Temperature and elevated CO2 alter soybean seed yield and quality, exhibiting transgenerational effects on seedling emergence and vigor

Introduction

Environmental conditions play a prime role in the growth and development of plant species, exerting a significant influence on their reproductive capacity. Soybean is sensitive to high temperatures during flowering and seed developmental stages. Little is known about the combined environmental effect of temperature and CO2 on seed yield and quality and its future generation.

Methods

A study was conducted to examine the effect of temperature (22/14°C (low), 30/22°C (optimum), and 38/30°C (high)), and CO2 (420 ppm (ambient; aCO2) and 720 ppm (elevated; eCO2)) on seed yield, quality, and transgenerational seedling vigor traits of soybean cultivars (DS25-1 and DS31-243) using Soil-Plant-Atmospheric-Research facility.

Results

A significant temperature effect was recorded among yield and quality attributes. At high-temperature, the 100-seed weights of DS25-1 and DS31-243 declined by 40% and 24%, respectively, over the optimum temperature at aCO2. The harvest index of varieties reduced by 70% when exposed to high temperature under both aCO2 and eCO2, compared to the optimum temperature at aCO2. The seed oil (- 2%) and protein (8%) content altered when developed under high temperature under aCO2. Maximum sucrose (7.5%) and stachyose (3.8%) accumulation in seeds were observed when developed under low temperatures and eCO2. When the growing temperature increased from optimum to high, the seed oleic acids increased (63%), while linoleic and linolenic acids decreased (- 28% and - 43%, respectively). Significant temperature and CO2 effects were observed in progenies with the highest maximum seedling emergence (80%), lesser time to 50% emergence (5.5 days), and higher seedling vigor from parents grown at low-temperature treatment under eCO2.

Discussion

Exposure of plants to 38/30°C was detrimental to soybean seed yield, and eCO2 levels did not compensate for this yield loss. The high temperature during seed developmental stages altered the chemical composition of the seed, leading to an increased content of monounsaturated fatty acids. The findings suggest that parental stress can significantly impact the development of offspring, indicating that epigenetic regulation or memory repose may be at play.

A review of the potential involvement of small RNAs in transgenerational abiotic stress memory in plants

Crop production is increasingly threatened by the escalating weather events and rising temperatures associated with global climate change. Plants have evolved adaptive mechanisms, including stress memory, to cope with abiotic stresses such as heat, drought, and salinity. Stress memory involves priming, where plants remember prior stress exposures, providing enhanced responses to subsequent stress events. Stress memory can manifest as somatic, intergenerational, or transgenerational memory, persisting for different durations. The chromatin, a central regulator of gene expression, undergoes modifications like DNA acetylation, methylation, and histone variations in response to abiotic stress. Histone modifications, such as H3K4me3 and acetylation, play crucial roles in regulating gene expression. Abiotic stresses like drought and salinity are significant challenges to crop production, leading to yield reductions. Plant responses to stress involve strategies like escape, avoidance, and tolerance, each influencing growth stages differently. Soil salinity affects plant growth by disrupting water potential, causing ion toxicity, and inhibiting nutrient uptake. Understanding plant responses to these stresses requires insights into histone-mediated modifications, chromatin remodeling, and the role of small RNAs in stress memory. Histone-mediated modifications, including acetylation and methylation, contribute to epigenetic stress memory, influencing plant adaptation to environmental stressors. Chromatin remodeling play a crucial role in abiotic stress responses, affecting the expression of stress-related genes. Small RNAs; miRNAs and siRNAs, participate in stress memory pathways by guiding DNA methylation and histone modifications. The interplay of these epigenetic mechanisms helps plants adapt to recurring stress events and enhance their resilience. In conclusion, unraveling the epigenetic mechanisms in plant responses to abiotic stresses provides valuable insights for developing resilient agricultural techniques. Understanding how plants utilize stress memory, histone modifications, chromatin remodeling, and small RNAs is crucial for designing strategies to mitigate the impact of climate change on crop production and global food security.

Novel insights into maize (Zea mays) development and organogenesis for agricultural optimization

In maize, intrinsic hormone activities and sap fluxes facilitate organogenesis patterning and plant holistic development; these hormone movements should be a primary focus of developmental biology and agricultural optimization strategies. Maize (Zea mays) is an important crop plant with distinctive life history characteristics and structural features. Genetic studies have extended our knowledge of maize developmental processes, genetics, and molecular ecophysiology. In this review, the classical life cycle and life history strategies of maize are analyzed to identify spatiotemporal organogenesis properties and develop a definitive understanding of maize development. The actions of genes and hormones involved in maize organogenesis and sex determination, along with potential molecular mechanisms, are investigated, with findings suggesting central roles of auxin and cytokinins in regulating maize holistic development. Furthermore, investigation of morphological and structural characteristics of maize, particularly node ubiquity and the alternate attachment pattern of lateral organs, yields a novel regulatory model suggesting that maize organ initiation and subsequent development are derived from the stimulation and interaction of auxin and cytokinin fluxes. Propositions that hormone activities and sap flow pathways control organogenesis are thoroughly explored, and initiation and development processes of distinctive maize organs are discussed. Analysis of physiological factors driving hormone and sap movement implicates cues of whole-plant activity for hormone and sap fluxes to stimulate maize inflorescence initiation and organ identity determination. The physiological origins and biogenetic mechanisms underlying maize floral sex determination occurring at the tassel and ear spikelet are thoroughly investigated. The comprehensive outline of maize development and morphogenetic physiology developed in this review will enable farmers to optimize field management and will provide a reference for de novo crop domestication and germplasm improvement using genome editing biotechnologies, promoting agricultural optimization.

Genome-wide identification of drought-responsive microRNAs and their target genes in Chinese jujube by deep sequencing

BACKGROUND

MicroRNAs (miRNAs) are about 21 snucleotide (nt) long, non-coding RNAs that play an important role in plant abiotic stress responses. Chinese jujube is a native fruit tree in China, which is also an admittedly drought-resistant plant. But the drought-related miRNAs have little been reported in jujube.

OBJECTIVE

To identify possibly drought-responsive microRNAs and their target genes in Chinese Jujube.

METHODS

Twelve small RNA libraries were constructed from two jujube genotypes both drought treated and control samples with three replicates to identify known and novel miRNAs in Chinese Jujube, DESeq2 was used to identify expression pattern of miRNAs between drought treatment and control samples, TargetFinder program was used to predict potential target genes of conserved and novel miRNAs, RT-qPCR were used to analysis the expression levels of drought-related miRNAs and their potential targets. The RNA ligase-mediated RLM-5' RACE experiments were performed to validate predicted target genes of drought-related miRNAs.

RESULTS

43 known miRNAs and 431 novel miRNAs were identified in Chinese jujube. Expression analysis showed that 28 miRNAs were differential expressed under drought stress in jujube variety "Dongzao", including 21 up-regulated miRNAs and 7 down-regulated miRNAs, 61 miRNAs were differential expressed under drought stress in Chinese jujube variety "Zanhuangdazao", including 23 up-regulated miRNAs and 37 down-regulated miRNAs. Depend on miRNAs target prediction, functional annotation and expression analysis, we identified 9 drought-related miRNAs, and 7 target genes of 6 miRNAs were confirmed using the modified 5'-RACE method. Also, RT-qPCR analyses revealed that relative expression of those miRNAs and their targets have negative tendency.

CONCLUSION

We identified 6 drought-related miRNAs by high-throughout sequencing and target gene annotation from Chinese jujube, and targets of those miRNAs were confirmed by the modified 5'-RACE method. These findings provide molecular evidence for enhancing drought tolerance in Chinese jujube and other plants.

Priming crops for the future: rewiring stress memory

The agricultural sector must produce resilient and climate-smart crops to meet the increasing needs of global food production. Recent advancements in elucidating the mechanistic basis of plant stress memory have provided new opportunities for crop improvement. Stress memory-coordinated changes at the organismal, cellular, and various omics levels prepare plants to be more responsive to reoccurring stress within or across generation(s). The exposure to a primary stress, or stress priming, can also elicit a beneficial impact when encountering a secondary abiotic or biotic stress through the convergence of synergistic signalling pathways, referred to as cross-stress tolerance. 'Rewired plants' with stress memory provide a new means to stimulate adaptable stress responses, safeguard crop reproduction, and engineer climate-smart crops for the future.

Combined drought and heat stresses trigger different sets of miRNAs in contrasting potato cultivars

MicroRNAs are small, non-coding RNAs that are responsible for regulation of gene expression during plant growth and development. Although there are many studies on miRNAs in other plants, little work has been done to understand the role of miRNAs in abiotic stress tolerance in potatoes. This study investigates changes in miRNA profiles of two different potato cultivars (tolerant, Unica and susceptible, Russet Burbank) in response to heat, drought and their combination. Transcriptomic studies revealed that miRNA profiles depend on the susceptibility and tolerance of the cultivar and also the stress conditions. Large number of miRNAs were expressed in Unica, whereas Russet Burbank indicated lesser number of changes in miRNA expression. Physiological and transcriptional results clearly supported that Unica cultivar is tolerant to combined drought and heat stress compared to Russet Burbank. Moreover, psRNATarget analysis predicted that major miRNAs identified were targeting genes playing important roles in response to drought and heat stress and their important roles in genetic and post-transcriptional regulation, root development, auxin responses and embryogenesis were also observed. This study focused on eight miRNAs (Novel_8, Novel_9, Novel_105, miR156d-3p, miR160a-5p, miR162a-3p, miR172b-3p and miR398a-5p) and their putative targets where results indicate that they may play a vital role at different post-transcriptional levels against drought and heat stresses. We suggest that miRNA overexpression in plants can lead to increased tolerance against abiotic stresses; furthermore, there should be more emphasis on the studies to investigate the role of miRNAs in combined abiotic stress in plants.

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.

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.

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 Key Candidate microRNAs and Target Genes Associated with Peanut Drought Tolerance

Peanut is an important crash crop worldwide, and it is often threatened by drought stress due to unexpected extreme weather events. In this work, NH5 and FH18 were selected as drought-tolerant and drought-sensitive varieties, respectively. Comparison of their physiological responses revealed that NH5 showed less wilting, higher relative water content and lower water loss rate of detached leaves, lower electrolyte leakage, and stronger antioxidant ability under drought stress than did FH18. Based on comparative transcriptomic analysis, 5376 differentially expressed mRNAs were commonly identified in the two varieties, and 2993 genes specifically changed in the drought-tolerant variety and were mainly enriched in photosynthesis-antenna proteins and photosynthetic pathways. Furthermore, 73 microRNAs (miRNAs) were differentially expressed in the drought tolerance variety specifically under drought stress; of these, two key candidate miRNAs, novel miR_416 and novel miR_73, were identified, and the majority of their target genes were enriched in phenylpropanoid biosynthesis, linoleic acid metabolism, and cutin, suberine, and wax biosynthesis. This study lays the foundation for the analysis of the molecular mechanism of drought tolerance and promotes the genetic improvement of peanut drought tolerance.

Multi-Omics Analysis of Small RNA, Transcriptome, and Degradome in T. turgidum-Regulatory Networks of Grain Development and Abiotic Stress Response

Crop reproduction is highly sensitive to water deficit and heat stress. The molecular networks of stress adaptation and grain development in tetraploid wheat (Triticum turgidum durum) are not well understood. Small RNAs (sRNAs) are important epigenetic regulators connecting the transcriptional and post-transcriptional regulatory networks. This study presents the first multi-omics analysis of the sRNAome, transcriptome, and degradome in T. turgidum developing grains, under single and combined water deficit and heat stress. We identified 690 microRNAs (miRNAs), with 84 being novel, from 118 sRNA libraries. Complete profiles of differentially expressed miRNAs (DEMs) specific to genotypes, stress types, and different reproductive time-points are provided. The first degradome sequencing report for developing durum grains discovered a significant number of new target genes regulated by miRNAs post-transcriptionally. Transcriptome sequencing profiled 53,146 T. turgidum genes, swith differentially expressed genes (DEGs) enriched in functional categories such as nutrient metabolism, cellular differentiation, transport, reproductive development, and hormone transduction pathways. miRNA-mRNA networks that affect grain characteristics such as starch synthesis and protein metabolism were constructed on the basis of integrated analysis of the three omics. This study provides a substantial amount of novel information on the post-transcriptional networks in T. turgidum grains, which will facilitate innovations for breeding programs aiming to improve crop resilience and grain quality.

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.

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.

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.

The Use of Nitrogen and Its Regulation in Cereals: Structural Genes, Transcription Factors, and the Role of miRNAs

Cereals and, especially, rice, maize, and wheat, are essential commodities, on which human nutrition is based. Expanding population and food demand have required higher production which has been achieved by increasing fertilization, and especially nitrogen supply to cereal crops. In fact, nitrogen is a crucial nutrient for the plant, but excessive use poses serious environmental and health issues. Therefore, increasing nitrogen use efficiency in cereals is of pivotal importance for sustainable agriculture. The main steps in the use of nitrogen are uptake and transport, reduction and assimilation, and translocation and remobilization. Many studies have been carried out on the genes involved in these phases, and on transcription factors regulating these genes. Lately, increasing attention has been paid to miRNAs responding to abiotic stress, including nutrient deficiency. Many miRNAs have been found to regulate transcription factors acting on the expression of specific genes for nitrogen uptake or remobilization. Recent studies on gene regulatory networks have also demonstrated that miRNAs can interact with several nodes in the network, functioning as key regulators in nitrogen metabolism.

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 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.

MicroRNA-guided regulation of heat stress response in wheat

Background

With rising global temperature, understanding plants’ adaptation to heat stress has implications in plant breeding. MicroRNAs (miRNAs) are small, non-coding, regulatory RNAs guiding gene expression at the post-transcriptional level. In this study, small RNAs and the degradome (parallel analysis of RNA ends) of leaf tissues collected from control and heat-stressed wheat plants immediately at the end of the stress period and 1 and 4 days later were analysed.

Results

Sequencing of 24 small RNA libraries produced 55.2 M reads while 404 M reads were obtained from the corresponding 24 PARE libraries. From these, 202 miRNAs were ascertained, of which mature miRNA evidence was obtained for 104 and 36 were found to be differentially expressed after heat stress. The PARE analysis identified 589 transcripts targeted by 84 of the ascertained miRNAs. PARE sequencing validated the targets of the conserved members of miRNA156, miR166 and miR393 families as squamosa promoter-binding-like, homeobox leucine-zipper and transport inhibitor responsive proteins, respectively. Heat stress responsive miRNA targeted superoxide dismutases and an array of homeobox leucine-zipper proteins, F-box proteins and protein kinases. Query of miRNA targets to interactome databases revealed a predominant association of stress responses such as signalling, antioxidant activity and ubiquitination to superoxide dismutases, F-box proteins, pentatricopeptide repeat-containing proteins and mitochondrial transcription termination factor-like proteins.

Conclusion

The interlaced data set generated in this study identified and validated heat stress regulated miRNAs and their target genes associated with thermotolerance. Such accurate identification and validation of miRNAs and their target genes are essential to develop novel regulatory gene-based breeding strategies.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5799-6) contains supplementary material, which is available to authorized users.

Profiling the Abiotic Stress Responsive microRNA Landscape of Arabidopsis thaliana

It is well established among interdisciplinary researchers that there is an urgent need to address the negative impacts that accompany climate change. One such negative impact is the increased prevalence of unfavorable environmental conditions that significantly contribute to reduced agricultural yield. Plant microRNAs (miRNAs) are key gene expression regulators that control development, defense against invading pathogens and adaptation to abiotic stress. Arabidopsis thaliana (Arabidopsis) can be readily molecularly manipulated, therefore offering an excellent experimental system to alter the profile of abiotic stress responsive miRNA/target gene expression modules to determine whether such modification enables Arabidopsis to express an altered abiotic stress response phenotype. Towards this goal, high throughput sequencing was used to profile the miRNA landscape of Arabidopsis whole seedlings exposed to heat, drought and salt stress, and identified 121, 123 and 118 miRNAs with a greater than 2-fold altered abundance, respectively. Quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) was next employed to experimentally validate miRNA abundance fold changes, and to document reciprocal expression trends for the target genes of miRNAs determined abiotic stress responsive. RT-qPCR also demonstrated that each miRNA/target gene expression module determined to be abiotic stress responsive in Arabidopsis whole seedlings was reflective of altered miRNA/target gene abundance in Arabidopsis root and shoot tissues post salt stress exposure. Taken together, the data presented here offers an excellent starting platform to identify the miRNA/target gene expression modules for future molecular manipulation to generate plant lines that display an altered response phenotype to abiotic stress.

Epigenetic responses to abiotic stresses during reproductive development in cereals

KEY MESSAGE

Overview of current understanding of epigenetic alterations after abiotic stresses during reproductive development in cereals. Abiotic stresses, including heat, drought, cold, flooding, and salinity, negatively impact crop productivity. Various stages during reproductive development are especially sensitive to environmental stresses, which may lead to complete sterility and severe yield losses. Plants exhibit diverse responses to ameliorate stress damage. Changes in DNA methylation, histone modification as well as regulation of small RNA and long noncoding RNA pathways have been shown to represent key modulators in plant stress responses. During reproductive development in cereals, various protein complexes controlling histone and DNA methylation have been identified, revealing conserved and novel mechanisms regulating abiotic stress responses in cereals and other plant species. New findings highlight the role of transposable elements during stress periods. Here, we review our current understanding of epigenetic stress responses during male and female gametophyte formation (germline development), fertilization, early seed devolvement, and seed maturation in cereals. An integrative model of epigenetic responses during reproductive development in cereals is proposed, emphasizing the role of DNA methylation and histone modifications during abiotic stresses.

Legume genetic resources and transcriptome dynamics under abiotic stress conditions

Grain legumes are an important source of nutrition and income for billions of consumers and farmers around the world. However, the low productivity of new legume varieties, due to the limited genetic diversity available for legume breeding programmes and poor policymaker support, combined with an increasingly unpredictable global climate is resulting in a large gap between current yields and the increasing demand for legumes as food. Hence, there is a need for novel approaches to develop new high-yielding legume cultivars that are able to cope with a range of environmental stressors. Next-generation technologies are providing the tools that could enable the more rapid and cost-effective genomic and transcriptomic studies for most major crops, allowing the identification of key functional and regulatory genes involved in abiotic stress resistance. In this review, we provide an overview of the recent achievements regarding abiotic stress resistance in a wide range of legume crops and highlight the transcriptomic and miRNA approaches that have been used. In addition, we critically evaluate the availability and importance of legume genetic resources with desirable abiotic stress resistance traits.

Identification of Blueberry miRNAs and Their Targets Based on High-Throughput Sequencing and Degradome Analyses

miRNAs are important regulators of plant gene expression. To better characterize their functions, we applied high-throughput sequencing and degradome analyses to investigate three blueberry (Vaccinium ashei) tissues. A total of 127 known and 101 novel miRNAs were identified. Moreover, 141 targets for 42 known and 19 novel miRNAs were experimentally validated by degradome sequencing. A functional analysis of these miRNA targets revealed they were associated with diverse biological activities and several pathways, e.g., anthocyanin biosynthesis and cytokinin signal transduction. The data presented herein expand our understanding of the regulation of blueberry miRNAs during floral and fruit development stages. They may also provide new insights into the roles of miRNAs during anthocyanin biosynthesis in blueberry fruits.

Identification of drought-responsive microRNAs in tomato using high-throughput sequencing

Drought is a major abiotic stress affecting crop productivity and quality. As a class of noncoding RNA, microRNA (miRNA) plays important roles in plant growth, development, and stress response. However, their response and roles in tomato drought stress is largely unknown. Here, by using high-throughput sequencing, we compared the miRNA profiles before and after drought treatment in two tomato genotypes: M82, a drought-sensitive cultivated tomato (Solanum lycopersicum), and IL2-5, a drought-tolerant introgression line derived from M82 and the tomato wild species S. pennellii (LA0716). A total of 108 conserved and 208 novel miRNAs were identified, among them, 32 and 68 were significantly changed in expression after stress. Further, 1936 putative target genes were predicted for those differentially-expressed miRNAs. Gene ontology and pathway analysis showed that many of the target genes were involved in stress resistance, such as genes in GO terms including response to stress, defense response, response to stimulus, phosphorylation, and signal transduction. Our results suggested that miRNAs play an essential role in the drought response of tomato. This work will help to further characterize specific miRNAs functioning in drought tolerance.

Durum wheat miRNAs in response to nitrogen starvation at the grain filling stage

Durum wheat highly depends on nitrogen for seed development and yield, and the obtainment of varieties with a better nitrogen use efficiency is crucial to reduce production costs and environmental pollution. In this study, sequencing of two small RNA libraries obtained from tissues of Ciccio and Svevo cultivars grown under nitrogen starvation conditions produced 84 novel, and 161 conserved miRNAs. Of these, 7 novel and 13 known miRNAs were newly identified in this work. Quantitative PCR analysis of selected miRNAs highlighted that the expression levels of some of them depends on the tissue and on the cultivar, Svevo being the most responsive to nitrogen starvation. A number of target genes were predicted to be involved in nitrogen metabolism. An inverse correlation for the qPCR expression data of miRNA/target pairs miR399b/PHO2, miR393c/AFB2, ttu-novel-61/CCAAT-TF was observed in specific tissues or cultivar. Especially, ttu-novel-61 was down-regulated and its target CCAAT-TF up-regulated in almost all tissues both in Svevo and in Ciccio. Moreover, CCAAT-TF was confirmed to be cleaved by ttu-novel-61 at the expected site. The discovery of miRNAs involved in the response to nitrogen stress represents an important step towards functional analyses, with the final aim to design strategies for improving nitrogen use efficiency in durum wheat.

Profiling of drought-responsive microRNA and mRNA in tomato using high-throughput sequencing

BACKGROUND

Abiotic stresses cause severe loss of crop production. Among them, drought is one of the most frequent environmental stresses, which limits crop growth, development and productivity. Plant drought tolerance is fine-tuned by a complex gene regulatory network. Understanding the molecular regulation of this polygenic trait is crucial for the eventual success to improve plant yield and quality. Recent studies have demonstrated that microRNAs play critical roles in plant drought tolerance. However, little is known about the microRNA in drought response of the model plant tomato. Here, we described the profiling of drought-responsive microRNA and mRNA in tomato using high-throughput next-generation sequencing.

RESULTS

Drought stress was applied on the seedlings of M82, a drought-sensitive cultivated tomato genotype, and IL9-1, a drought-tolerant introgression line derived from the stress-resistant wild species Solanum pennellii LA0716 and M82. Under drought, IL9-1 performed superior than M82 regarding survival rate, H2O2 elimination and leaf turgor maintenance. A total of four small RNA and eight mRNA libraries were constructed and sequenced using Illumina sequencing technology. 105 conserved and 179 novel microRNAs were identified, among them, 54 and 98 were differentially expressed upon drought stress, respectively. The majority of the differentially-expressed conserved microRNAs was up-regulated in IL9-1 whereas down-regulated in M82. Under drought stress, 2714 and 1161 genes were found to be differentially expressed in M82 and IL9-1, respectively, and many of their homologues are involved in plant stress, such as genes encoding transcription factor and protein kinase. Various pathways involved in abiotic stress were revealed by Gene Ontology and pathway analysis. The mRNA sequencing results indicated that most of the target genes were regulated by their corresponding microRNAs, which suggested that microRNAs may play essential roles in the drought tolerance of tomato.

CONCLUSION

In this study, numerous microRNAs and mRNAs involved in the drought response of tomato were identified using high-throughput sequencing, which will provide new insights into the complex regulatory network of plant adaption to drought stress. This work will also help to exploit new players functioning in plant drought-stress tolerance.

Translating knowledge about abiotic stress tolerance to breeding programmes

Plant breeding and improvements in agronomic practice are making a consistent contribution to increasing global crop production year upon year. However, the rate of yield improvement currently lags behind the targets set to produce enough food to meet the demands of the predicted global population in 2050. Furthermore, crops that are exposed to harmful abiotic environmental factors (abiotic stresses, e.g. water limitation, salinity, extreme temperature) are prone to reduced yields. Here, we briefly describe the processes undertaken in conventional breeding programmes, which are usually designed to improve yields in near-optimal conditions rather than specifically breeding for improved crop yield stability under stressed conditions. While there is extensive fundamental research activity that examines mechanisms of plant stress tolerance, there are few examples that apply this research to improving commercial crop yields. There are notable exceptions, and we highlight some of these to demonstrate the magnitude of yield gains that could be made by translating agronomic, phenological and genetic solutions focused on improving or mitigating the effect of abiotic stress in the field; in particular, we focus on improvements in crop water-use efficiency and salinity tolerance. We speculate upon the reasons for the disconnect between research and research translation. We conclude that to realise untapped rapid gains towards food security targets new funding structures need to be embraced. Such funding needs to serve both the core and collaborative activities of the fundamental, pre-breeding and breeding research communities in order to expedite the translation of innovative research into the fields of primary producers.

Genotypic water-deficit stress responses in durum wheat: association between physiological traits, microRNA regulatory modules and yield components

In Mediterranean environments, water-deficit stress that occurs before anthesis significantly limits durum wheat (Triticum turgidum L. ssp. durum) production. Stress tolerant and stress sensitive durum varieties exhibit genotypic differences in their response to pre-anthesis water-deficit stress as reflected by yield performance, but our knowledge of the mechanisms underlying tolerance is limited. We have previously identified stress responsive durum microRNAs (miRNAs) that could contribute to water-deficit stress tolerance by mediating post-transcriptional silencing of genes that lead to stress adaptation (e.g. miR160 and its targets ARF8 (auxin response factor 8) and ARF18). However, the temporal regulation pattern of miR160-ARFs after induction of pre-anthesis water-deficit stress in sensitive and tolerant varieties remains unknown. Here, the physiological responses of four durum genotypes are described by chlorophyll content, leaf relative water content, and stomatal conductance at seven time-points during water-deficit stress from booting to anthesis. qPCR examination of miR160, ARF8 and ARF18 at these time-points revealed a complex stress responsive regulatory pattern, in the flag leaf and the head, subject to genotype. Harvest components and morphological traits measured at maturity confirmed the stress tolerance level of these four varieties for agronomic performance, and their potential association with the physiological responses. In general, the distinct regulatory pattern of miR160-ARFs among stress tolerant and sensitive durum varieties suggests that miRNA-mediated molecular pathways may contribute to the genotypic differences in the physiological traits, ultimately affecting yield components (e.g. the maintenance of harvest index and grain number).

Identification of Drought-Responsive MicroRNAs from Roots and Leaves of Alfalfa by High-Throughput Sequencing

Alfalfa, an important forage legume, is an ideal crop for sustainable agriculture and a potential crop for bioenergy resources. Drought, one of the most common environmental stresses, substantially affects plant growth, development, and productivity. MicroRNAs (miRNAs) are newly discovered gene expression regulators that have been linked to several plant stress responses. To elucidate the role of miRNAs in drought stress regulation of alfalfa, a high-throughput sequencing approach was used to analyze 12 small RNA libraries comprising of four samples, each with three biological replicates. From the 12 libraries, we identified 348 known miRNAs belonging to 80 miRNA families, and 281 novel miRNAs, using Mireap software. Eighteen known miRNAs in roots and 12 known miRNAs in leaves were screened as drought-responsive miRNAs. With the exception of miR319d and miR157a which were upregulated under drought stress, the expression pattern of drought-responsive miRNAs was different between roots and leaves in alfalfa. This is the first study that has identified miR3512, miR3630, miR5213, miR5294, miR5368 and miR6173 as drought-responsive miRNAs. Target transcripts of drought-responsive miRNAs were computationally predicted. All 447 target genes for the known miRNAs were predicted using an online tool. This study provides a significant insight on understanding drought-responsive mechanisms of alfalfa.

Identification and characterization of durum wheat microRNAs in leaf and root tissues

MicroRNAs are a class of post-transcriptional regulators of plant developmental and physiological processes and responses to environmental stresses. Here, we present the study regarding the annotation and characterization of MIR genes conducted in durum wheat. We characterized the miRNAome of leaf and root tissues at tillering stage under two environmental conditions: irrigated with 100% (control) and 55% of evapotranspiration (early water stress). In total, 90 microRNAs were identified, of which 32 were classified as putative novel and species-specific miRNAs. In addition, seven microRNA homeologous groups were identified in each of the two genomes of the tetraploid durum wheat. Differential expression analysis highlighted a total of 45 microRNAs significantly differentially regulated in the pairwise comparisons leaf versus root. The miRNA families, miR530, miR395, miR393, miR5168, miR396 and miR166, miR171, miR319, and miR167, were the most expressed in leaves in comparison to roots. Putative microRNA targets were predicted for both five and three prime sequences derived from the stem-loop of the MIR gene. Gene ontology analysis showed significant overrepresented gene categories in microRNA targets belonging to transcription factors, phenylpropanoids, oxydases, and lipid binding-protein. This work represents one of the first genome wide characterization of MIR genes in durum wheat, identifying leaf and root tissue-specific microRNAs. This genomic identification of microRNAs together with the analysis of their expression profiles is a well-accepted starting point leading to a better comprehension of the role of MIR genes in the genus Triticum.

Drought-inducible expression of Hv-miR827 enhances drought tolerance in transgenic barley

Drought is one of the major abiotic stresses reducing crop yield. Since the discovery of plant microRNAs (miRNAs), considerable progress has been made in clarifying their role in plant responses to abiotic stresses, including drought. miR827 was previously reported to confer drought tolerance in transgenic Arabidopsis. We examined barley (Hordeum vulgare L. 'Golden Promise') plants over-expressing miR827 for plant performance under drought. Transgenic plants constitutively expressing CaMV-35S::Ath-miR827 and drought-inducible Zm-Rab17::Hv-miR827 were phenotyped by non-destructive imaging for growth and whole plant water use efficiency (WUE_wp). We observed that the growth, WUE_wp, time to anthesis and grain weight of transgenic barley plants expressing CaMV-35S::Ath-miR827 were negatively affected in both well-watered and drought-treated growing conditions compared with the wild-type plants. In contrast, transgenic plants over-expressing Zm-Rab17::Hv-miR827 showed improved WUE_wp with no growth or reproductive timing change compared with the wild-type plants. The recovery of Zm-Rab17::Hv-miR827 over-expressing plants also improved following severe drought stress. Our results suggest that Hv-miR827 has the potential to improve the performance of barley under drought and that the choice of promoter to control the timing and specificity of miRNA expression is critical.

Water-deficit stress-responsive microRNAs and their targets in four durum wheat genotypes

MicroRNAs (miRNAs) guide regulation at the post-transcriptional level by inducing messenger RNA (mRNA) degradation or translational inhibition of their target protein-coding genes. Durum wheat miRNAs may contribute to the genotypic water-deficit stress response in different durum varieties. Further investigation of the interactive miRNA-target regulatory modules and experimental validation of their response to water stress will contribute to our understanding of the small RNA-mediated molecular networks underlying stress adaptation in durum wheat. In this study, a comprehensive genome-wide in silico analysis using the updated Triticum transcriptome assembly identified 2055 putative targets for 113 conserved durum miRNAs and 131 targets for four novel durum miRNAs that putatively contribute to genotypic stress tolerance. Predicted mRNA targets encode various transcription factors, binding proteins and functional enzymes, which play vital roles in multiple biological pathways such as hormone signalling and metabolic processes. Quantitative PCR profiling further characterised 43 targets and 5 miRNAs with stress-responsive and/or genotype-dependent differential expression in two stress-tolerant and two stress-sensitive durum genotypes subjected to pre-anthesis water-deficit stress. Furthermore, a 5' RLM-RACE approach validated nine mRNA targets cleaved by water-deficit stress-responsive miRNAs, which, to our knowledge, has not been previously reported in durum wheat. The present study provided experimental evidence of durum miRNAs and target genes in response to water-deficit stress in contrasting durum varieties, providing new insights into the regulatory roles of the miRNA-guided RNAi mechanism underlying stress adaptation in durum wheat.