Homeostasis in the soybean miRNA396-GRF network is essential for productive soybean cyst nematode infections

The miR396a-SlGRF8 module regulates sugar accumulation in the roots via SlSTP10 during the interaction between root-knot nematodes and tomato plants

Root-knot nematodes (RKNs; Meloidogyne spp.) are a serious threat to crop production. The competition between plants and pathogens for assimilates influences the outcome of their interactions. However, the mechanisms by which plants and nematodes compete with each other for assimilates have not been elucidated. In this study, we demonstrated that miR396a plays a negative role in defense against RKNs and a positive role in sugar accumulation in tomato roots. The overexpression of SlGRF8 (Solanum lycopersicum growth-regulating factor 8), the target of miR396a, decreased the sugar content of the roots and the susceptibility to RKNs, whereas the grf8-cr mutation had the opposite effects. Furthermore, we confirmed that SlGRF8 regulated the sugar content in roots by directly activating the transcription of SlSTP10 (Solanum lycopersicum sugar transporter protein 10) in response to RKN stress. Moreover, SlSTP10 was expressed primarily in the tissues surrounding giant cells, and the SlSTP10 knockout increased both the sugar content in the roots and the plant's susceptibility to RKNs. Overall, this study provides important insight into the molecular mechanism through which the miR396a-SlGRF8-SlSTP10 module regulates sugar allocation in roots under RKN stress.

Functional Identification of miR2119 Targeting ADHs in Modulating Soybean Resistance to Heterodera glycines

Soybean cyst nematode (SCN, Heterodera glycines) is a sedentary endoparasite nematode that results in severe economic losses in soybean crops. miRNAs play crucial roles in plant responses to nematode. However, the role of miR2119 responding to SCN stress in soybean. Here, we demonstrated that the transcript levels of polycistronic precursors containing miR2119 and miR398a were significantly reduced in soybean upon nematode infection. Promoter of the miR2119-398a precursor analysis was conducted containing a GUS reporter gene. GUS activity assays demonstrated a decrease in miR2119-398a promoter during SCN infection. Overexpression of polycistronic precursor miR2119-398a (OE-premiR2119-398a) and miR2119 precursor (OE-premiR2119) rendered soybean more susceptible to SCN. Conversely, silencing miR2119 (STTM2119) increased soybean resistance against SCN. Furthermore, RNA-seq analysis revealed that miR2119 is involved in many defense signaling pathways. GUS reporter gene assays demonstrated that miR2119 targets GmADH1.1a and GmADH1.1b. Functional analysis indicated that ADHs act as a major role in responding to H. glycines by modulating reactive oxygen species (ROS) levels. Together, the findings reveal a novel mechanism by which the polycistronic precursor miR2119-398a coordinately regulates in response to H. glycines. Additionally, miR2119 becomes an essential element contributing to H. glycines by modulating ADH activity and ROS homeostasis in soybean.

ldi-miR396-LdPMaT1 enhances reactive oxygen species scavenging capacity and promotes drought tolerance in Lilium distichum Nakai autotetraploids

Drought is a key environmental stress that inhibits plant growth, development, yield and quality. Whole-genome replication is an effective method for breeding drought resistant cultivars. Here, we evaluated the tolerance of Lilium distichum Nakai diploids (2n = 2× = 24) and artificially induced autotetraploids (2n = 4× = 48) to drought simulated by polyethylene glycol (PEG) stress. Autotetraploids showed stronger drought tolerance than diploids, and high-throughput sequencing during PEG stress identified five differentially expressed miRNAs. Transcriptome analysis revealed significantly different reactive oxygen species (ROS)-scavenger expression levels between diploids and autotetraploids, which increased the drought tolerance of autotetraploids. Specifically, we identified ldi-miR396b and its only target gene (LdPMaT1) for further study based on its expression level and ROS-scavenging ability in response to drought stress (DS). Autotetraploids showed higher expression of LdPMaT1 and significantly downregulated expression of ldi-miR396b under DS compared with diploids. Through a short tandem target mimic (STTM) in transgenic lilies, functional studies revealed that miR396b silencing promotes LdPMaT1 expression and the DS response. Under PEG stress, STTM393 transgenic lines showed improved drought resistance mediated by lowered MDA content but exhibited high antioxidant enzyme activity, consistent with the autotetraploid results. Collectively, these findings suggest that ldi-miR396b-LdPMaT1 potentially enhances ROS-scavenging ability, which contributes to improved stress adaptation in autotetraploid lilies.

Knockout of miR396 genes increases seed size and yield in soybean

Yield improvement has long been an important task for soybean breeding in the world in order to meet the increasing demand for food and animal feed. miR396 genes have been shown to negatively regulate grain size in rice, but whether miR396 family members may function in a similar manner in soybean is unknown. Here, we generated eight soybean mutants harboring different combinations of homozygous mutations in the six soybean miR396 genes through genome editing with clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas)12SF01 in the elite soybean cultivar Zhonghuang 302 (ZH302). Four triple mutants (mir396aci, mir396acd, mir396adf, and mir396cdf), two quadruple mutants (mir396abcd and mir396acfi), and two quintuple mutants (mir396abcdf and mir396bcdfi) were characterized. We found that plants of all the mir396 mutants produced larger seeds compared to ZH302 plants. Field tests showed that mir396adf and mir396cdf plants have significantly increased yield in growth zones with relatively high latitude which are suited for ZH302 and moderately increased yield in lower latitude. In contrast, mir396abcdf and mir396bcdfi plants have increased plant height and decreased yield in growth zones with relatively high latitude due to lodging issues, but they are suited for low latitude growth zones with increased yield without lodging problems. Taken together, our study demonstrated that loss-of-function of miR396 genes leads to significantly enlarged seed size and increased yield in soybean, providing valuable germplasms for breeding high-yield soybean.

Conceptual Framework of Epigenetic Analyses of Plant Responses to Sedentary Endoparasitic Nematodes

Epigenetic modifications including miRNA regulation, DNA methylation, and histone modifications play fundamental roles in establishing the interactions between host plants and parasitic nematodes. Over the past decade, an increasing number of studies revealed the key functions of various components of the plant epigenome in the regulation of gene expression and shaping plant responses to nematode infection. In this chapter, we provide a conceptual framework for methods used to investigate epigenetic regulation during plant-nematode interactions. We focus specifically on current and emerging methods used to study miRNA regulation and function. We also highlight various methods and analytical tools used to profile DNA methylation patterns and histone modification marks at the genome level. Our intention is simply to explain the advantages of various methods and how to overcome some limitations. With rapid development of single-cell sequencing technology and genome editing, advanced and new methodologies are expected to emerge in the near future to further improve our understanding of epigenetic regulation and function during plant-nematode interactions.

Genome‑wide identification and characterization of miR396 family members and their target genes GRF in sorghum (Sorghum bicolor (L.) moench)

MicroRNAs (miRNAs) widely participate in plant growth and development. The miR396 family, one of the most conserved miRNA families, remains poorly understood in sorghum. To reveal the evolution and expression pattern of Sbi-miR396 gene family in sorghum, bioinformatics analysis and target gene prediction were performed on the sequences of the Sbi-miR396 gene family members. The results showed that five Sbi-miR396 members, located on chromosomes 4, 6, and 10, were identified at the whole-genome level. The secondary structure analysis showed that the precursor sequences of all five Sbi-miR396 potentially form a stable secondary stem-loop structure, and the mature miRNA sequences were generated on the 5' arm of the precursors. Sequence analysis identified the mature sequences of the five sbi-miR396 genes were high identity, with differences only at the 1st, 9th and 21st bases at the 5' end. Phylogenetic analysis revealed that Sbi-miR396a, Sbi-miR396b, and Sbi-miR396c were clustered into Group I, and Sbi-miR396d and Sbi-miR396e were clustered into Group II, and all five sbi-miR396 genes were closely related to those of maize and foxtail millet. Expression analysis of different tissue found that Sbi-miR396d/e and Sbi-miR396a/b/c were preferentially and barely expressed, respectively, in leaves, flowers, and panicles. Target gene prediction indicates that the growth-regulating factor family members (SbiGRF1/2/3/4/5/6/7/8/10) were target genes of Sbi-miR396d/e. Thus, Sbi-miR396d/e may affect the growth and development of sorghum by targeting SbiGRFs. In addition, expression analysis of different tissues and developmental stages found that all Sbi-miR396 target genes, SbiGRFs, were barely expressed in leaves, root and shoot, but were predominantly expressed in inflorescence and seed development stage, especially SbiGRF1/5/8. Therefore, inhibition the expression of sbi-miR396d/e may increase the expression of SbiGRF1/5/8, thereby affecting floral organ and seed development in sorghum. These findings provide the basis for studying the expression of the Sbi-mir396 family members and the function of their target genes.

Growth-regulating factors: conserved and divergent roles in plant growth and development and potential value for crop improvement

High yield and stress resistance are the major prerequisites for successful crop cultivation, and can be achieved by modifying plant architecture. Evolutionarily conserved growth-regulating factors (GRFs) control the growth of different tissues and organs of plants. Here, we provide a systematic overview of the expression patterns of GRF genes and the structural features of GRF proteins in different plant species. Moreover, we illustrate the conserved and divergent roles of GRFs, microRNA396 (miR396), and GRF-interacting factors (GIFs) in leaf, root, and flower development. We also describe the molecular networks involving the miR396-GRF-GIF module, and illustrate how this module coordinates with different signaling molecules and transcriptional regulators to control development of different plant species. GRFs promote leaf growth, accelerate grain filling, and increase grain size and weight. We also provide some molecular insight into how coordination between GRFs and other signaling modules enhances crop productivity; for instance, how the GRF-DELLA interaction confers yield-enhancing dwarfism while increasing grain yield. Finally, we discuss how the GRF-GIF chimera substantially improves plant transformation efficiency by accelerating shoot formation. Overall, we systematically review the conserved and divergent roles of GRFs and the miR396-GRF-GIF module in growth regulation, and also provide insights into how GRFs can be utilized to improve the productivity and nutrient content of crop plants.

Understandings and future challenges in soybean functional genomics and molecular breeding

Soybean (Glycine max) is a major source of plant protein and oil. Soybean breeding has benefited from advances in functional genomics. In particular, the release of soybean reference genomes has advanced our understanding of soybean adaptation to soil nutrient deficiencies, the molecular mechanism of symbiotic nitrogen (N) fixation, biotic and abiotic stress tolerance, and the roles of flowering time in regional adaptation, plant architecture, and seed yield and quality. Nevertheless, many challenges remain for soybean functional genomics and molecular breeding, mainly related to improving grain yield through high-density planting, maize-soybean intercropping, taking advantage of wild resources, utilization of heterosis, genomic prediction and selection breeding, and precise breeding through genome editing. This review summarizes the current progress in soybean functional genomics and directs future challenges for molecular breeding of soybean.

Genome-wide analysis of growth-regulating factor genes in grape (Vitis vinifera L.): identification, characterization and their responsive expression to osmotic stress

Identification, characterization and osmotic stress responsive expression of growth-regulating factor genes in grape. The growth and fruit production of grape vine are severely affected by adverse environmental conditions. Growth-regulating factors (GRFs) play a vital role in the regulation of plant growth, reproduction and stress tolerance. However, their biological functions in fruit vine crops are still largely unknown. In the present study, a total number of nine VvGRFs were identified in the grape genome. Phylogenetic and collinear relationship analysis revealed that they formed seven subfamilies, and have gone through three segmental duplication events. All VvGRFs were predicted to be nucleic localized and contained both the conserved QLQ and WRC domains at their N-terminals, one of the typical structural features of GRF proteins. Quantitative real-time PCR analyses demonstrated that all VvGRFs, with a predominant expression of VvGRF7, were constitutively expressed in roots, leaves and stems of grape plants, and showed responsive expression to osmotic stress. Further growth phenotypic analysis demonstrated that ectopic expression of VvGRF7 promoted the growth and sensitivity of transgenic Arabidopsis plants to osmotic stress. Our findings provide important information for the future study of VvGRF gene functions, and potential gene resources for the genetic breeding of new fruit vine varieties with improved fruit yield and stress tolerance.

Integrated Omic Approaches Reveal Molecular Mechanisms of Tolerance during Soybean and Meloidogyne incognita Interactions

The root-knot nematode (RKN), Meloidogyne incognita, is a devastating soybean pathogen worldwide. The use of resistant cultivars is the most effective method to prevent economic losses caused by RKNs. To elucidate the mechanisms involved in resistance to RKN, we determined the proteome and transcriptome profiles from roots of susceptible (BRS133) and highly tolerant (PI 595099) Glycine max genotypes 4, 12, and 30 days after RKN infestation. After in silico analysis, we described major defense molecules and mechanisms considered constitutive responses to nematode infestation, such as mTOR, PI3K-Akt, relaxin, and thermogenesis. The integrated data allowed us to identify protein families and metabolic pathways exclusively regulated in tolerant soybean genotypes. Among them, we highlighted the phenylpropanoid pathway as an early, robust, and systemic defense process capable of controlling M. incognita reproduction. Associated with this metabolic pathway, 29 differentially expressed genes encoding 11 different enzymes were identified, mainly from the flavonoid and derivative pathways. Based on differential expression in transcriptomic and proteomic data, as well as in the expression profile by RT-qPCR, and previous studies, we selected and overexpressed the GmPR10 gene in transgenic tobacco to assess its protective effect against M. incognita. Transgenic plants of the T₂ generation showed up to 58% reduction in the M. incognita reproduction factor. Finally, data suggest that GmPR10 overexpression can be effective against the plant parasitic nematode M. incognita, but its mechanism of action remains unclear. These findings will help develop new engineered soybean genotypes with higher performance in response to RKN infections.

Genome-wide identification and expression profile of GhGRF gene family in Gossypium hirsutum L

Background

Cotton is the primary source of renewable natural fiber in the textile industry and an important biodiesel crop. Growth regulating factors (GRFs) are involved in regulating plant growth and development.

Methods

Using genome-wide analysis, we identified 35 GRF genes in Gossypium hirsutum.

Results

Chromosomal location information revealed an uneven distribution of GhGRF genes, with maximum genes on chromosomes A02, A05, and A12 from the At sub-genome and their corresponding D05 and D12 from the Dt sub-genome. In the phylogenetic tree, 35 GRF genes were divided into five groups, including G1, G2, G3, G4, and G5. The majority of GhGRF genes have two to three introns and three to four exons, and their deduced proteins contained conserved QLQ and WRC domains in the N-terminal end of GRFs in Arabidopsis and rice. Sequence logos revealed that GRF genes were highly conserved during the long-term evolutionary process. The CDS of the GhGRF gene can complement MiRNA396a. Moreover, most GhGRF genes transcripts developed high levels of ovules and fibers. Analyses of promoter cis-elements and expression patterns indicated that GhGRF genes play an essential role in regulating plant growth and development by coordinating the internal and external environment and multiple hormone signaling pathways. Our analysis indicated that GhGRFs are ideal target genes with significant potential for improving the molecular structure of cotton.

Progress in soybean functional genomics over the past decade

Soybean is one of the most important oilseed and fodder crops. Benefiting from the efforts of soybean breeders and the development of breeding technology, large number of germplasm has been generated over the last 100 years. Nevertheless, soybean breeding needs to be accelerated to meet the needs of a growing world population, to promote sustainable agriculture and to address future environmental changes. The acceleration is highly reliant on the discoveries in gene functional studies. The release of the reference soybean genome in 2010 has significantly facilitated the advance in soybean functional genomics. Here, we review the research progress in soybean omics (genomics, transcriptomics, epigenomics and proteomics), germplasm development (germplasm resources and databases), gene discovery (genes that are responsible for important soybean traits including yield, flowering and maturity, seed quality, stress resistance, nodulation and domestication) and transformation technology during the past decade. At the end, we also briefly discuss current challenges and future directions.

Differential microRNA expression, microRNA arm switching, and microRNA:long noncoding RNA interaction in response to salinity stress in soybean

BACKGROUND

Soybean is a major legume crop with high nutritional and environmental values suitable for sustainable agriculture. Noncoding RNAs (ncRNAs), including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), are important regulators of gene functions in eukaryotes. However, the interactions between these two types of ncRNAs in the context of plant physiology, especially in response to salinity stress, are poorly understood.

RESULTS

Here, we challenged a cultivated soybean accession (C08) and a wild one (W05) with salt treatment and obtained their small RNA transcriptomes at six time points from both root and leaf tissues. In addition to thoroughly analyzing the differentially expressed miRNAs, we also documented the first case of miRNA arm-switching (miR166m), the swapping of dominant miRNA arm expression, in soybean in different tissues. Two arms of miR166m target different genes related to salinity stress (chloroplastic beta-amylase 1 targeted by miR166m-5p and calcium-dependent protein kinase 1 targeted by miR166m-3p), suggesting arm-switching of miR166m play roles in soybean in response to salinity stress. Furthermore, two pairs of miRNA:lncRNA interacting partners (miR166i-5p and lncRNA Gmax_MSTRG.35921.1; and miR394a-3p and lncRNA Gmax_MSTRG.18616.1) were also discovered in reaction to salinity stress.

CONCLUSIONS

This study demonstrates how ncRNA involves in salinity stress responses in soybean by miRNA arm switching and miRNA:lncRNA interactions. The behaviors of ncRNAs revealed in this study will shed new light on molecular regulatory mechanisms of stress responses in plants, and hence provide potential new strategies for crop improvement.

Soybean miR159-GmMYB33 Regulatory Network Involved in Gibberellin-Modulated Resistance to Heterodera glycines

Soybean cyst nematode (SCN, Heterodera glycines) is an obligate sedentary biotroph that poses major threats to soybean production globally. Recently, multiple miRNAome studies revealed that miRNAs participate in complicated soybean-SCN interactions by regulating their target genes. However, the functional roles of miRNA and target genes regulatory network are still poorly understood. In present study, we firstly investigated the expression patterns of miR159 and targeted GmMYB33 genes. The results showed miR159-3p downregulation during SCN infection; conversely, GmMYB33 genes upregulated. Furthermore, miR159 overexpressing and silencing soybean hairy roots exhibited strong resistance and susceptibility to H. glycines, respectively. In particular, miR159-GAMYB genes are reported to be involve in GA signaling and metabolism. Therefore, we then investigated the effects of GA application on the expression of miR159-GAMYB module and the development of H. glycines. We found that GA directly controls the miR159-GAMYB module, and exogenous GA application enhanced endogenous biologically active GA1 and GA3, the abundance of miR159, lowered the expression of GmMYB33 genes and delayed the development of H. glycines. Moreover, SCN infection also results in endogenous GA content decreased in soybean roots. In summary, the soybean miR159-GmMYB33 module was directly involved in the GA-modulated soybean resistance to H. glycines.

Genetic toolbox and regulatory circuits of plant-nematode associations

Plant-nematode associations are the most imperative area of study that forms the basis to understand their regulatory networks and coordinated functional aspects. Nematodes are highly parasitic organisms known so far, to cause relentless damage towards agricultural crops on a global scale. They pierce the roots of host plants and form neo-plastic feeding structures to extract out resources for their functional development. Moreover, they undergo re-differentiation within plant cells to form giant multi-nucleate feeding structures or syncytium. All these processes are facilitated by numerous transcriptomic, proteomic, metabolomic and epigenetic modifications, that regulate different biological attractions among plants and nematodes. Nevertheless, these mechanisms are quite remarkable and have been explored in the present review. Here, we have shed light on genomic as well as genetic approaches to acquire an effective understanding regarding plant-nematode associations. Transcriptomics have revealed an extensive network to unravel feeding mechanism of nematodes through gene-expression programming of target genes. Also, the regulatory circuits of epigenetic alterations through DNA-methylation, non-coding RNAs and histone modifications very well explain epigenetic profiling within plants. Since decades, research have observed many intricacies to elucidate the dynamic nature of epigenetic modulations in plant-nematode attractions. By this review, we have highlighted the functional aspects of small RNAs in inducing plant-nematode parasitism along with the putative role of miRNAs. These RNAs act as chief genetic elements to mediate the expressional changes in plants through post-transcriptional silencing of various effector proteins as well as transcriptional factors. A pragmatic role of miRNAs in modulating gene expression in nematode infection and feeding site development have also been reviewed. Hence, they have been considered master regulators for functional reprogramming the expression during establishment of feeding sites. We have also encapsulated the advancement of genome-broadened DNA-methylation and untangled the nematode mediated dynamic alterations within plant methylome along with assessing transcriptional activities of various genes and transposons. In particular, we have highlighted the role of effector proteins in stimulating epigenetic changes. Finally, we have emerged towards a molecular-based core understanding about plant-nematode associations.

MiR396-GRF module associates with switchgrass biomass yield and feedstock quality

Improving plant biomass yield and/or feedstock quality for highly efficient lignocellulose conversion has been the main research focus in genetic modification of switchgrass (Panicum virgatum L.), a dedicated model plant for biofuel production. Here, we proved that overexpression of miR396 (OE-miR396) leads to reduced plant height and lignin content mainly by reducing G-lignin monomer content. We identified nineteen PvGRFs in switchgrass and proved thirteen of them were cleaved by miR396. MiR396-targeted PvGRF1, PvGRF9 and PvGRF3 showed significantly higher expression in stem. By separately overexpressing rPvGRF1, 3 and 9, in which synonymous mutations abolished the miR396 target sites, and suppression of PvGRF1/3/9 activity via PvGRF1/3/9-SRDX overexpression in switchgrass, we confirmed PvGRF1 and PvGRF9 played positive roles in improving plant height and G-lignin content. Overexpression of PvGRF9 was sufficient to complement the defective phenotype of OE-miR396 plants. MiR396-PvGRF9 modulates these traits partly by interfering GA and auxin biosynthesis and signalling transduction and cell wall lignin, glucose and xylan biosynthesis pathways. Moreover, by enzymatic hydrolysis analyses, we found that overexpression of rPvGRF9 significantly enhanced per plant sugar yield. Our results suggest that PvGRF9 can be utilized as a candidate molecular tool in modifying plant biomass yield and feedstock quality.

Small RNA and degradome deep sequencing reveals important roles of microRNAs in cotton (Gossypium hirsutum L.) response to root-knot nematode Meloidogyne incognita infection

Investigation of cotton response to nematode infection will allow us to better understand the cotton immune defense mechanism and design a better biotechnological approach for efficiently managing pest nematodes in cotton. In this study, we firstly treated cotton by root knot nematode (RKN, Meloidogyne incognita) infections, then we employed the high throughput deep sequencing technology to sequence and genome-widely identify all miRNAs in cotton; finally, we analyzed the functions of these miRNAs in cotton response to RKN infections. A total of 266 miRNAs, including 193 known and 73 novel miRNAs, were identified by deep sequencing technology, which belong to 67 conserved and 66 novel miRNA families, respectively. A majority of identified miRNA families only contain one miRNA; however, miR482 family contains 14 members and some others contain 2-13 members. Certain miRNAs were specifically expressed in RKN-infected cotton roots and others were completely inhibited by RKN infection. A total of 50 miRNAs were differentially expressed after RKN infection, in which 28 miRNAs were up-regulated and 22 were inhibited by RKN treatment. Based on degradome sequencing, 87 gene targets were identified to be targeted by 57 miRNAs. These miRNA-targeted genes are involved in the interaction of cotton plants and nematode infection. Based on GO (gene ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis, 466 genes from all 636 miRNA targets were mapped to 6340 GO terms, 181 genes from 228 targets of differentially expressed miRNAs were mapped to 1588 GO terms. The GO terms were then categorized into the three main GO classes: biological processes, cellular components, and molecular functions. The targets of differentially expressed miRNAs were enriched in 43 GO terms, including 22 biological processes, 10 cellular components, and 11 molecular functions (p < 0.05). Many identified processes were associated with organism responses to the environmental stresses, including regulation of nematode larval development, response to nematode, and response to flooding. Our results will enhance the study and application of developing new cotton cultivars for nematode resistance.

smi-miR396b targeted SmGRFs, SmHDT1, and SmMYB37/4 synergistically regulates cell growth and active ingredient accumulation in Salvia miltiorrhiza hairy roots

MIR396b had been cloned and overexpressed in Salvia miltiorrhiza hairy roots. MiR396b targets SmGRFs, SmHDT1, and SmMYB37/4 to regulate cell growth and secondary metabolism in S. miltiorrhiza hairy roots. Danshen (Salvia miltiorrhiza Bunge) is a valuable medicinal herb with two kinds of clinically used natural products, salvianolic acids and tanshinones. miR396 is a conserved microRNA and plays extensive roles in plants. However, it is still unclear how miR396 works in S. miltiorrhiza. In this study, an smi-MIR396b has been cloned from S. miltiorrhiza. Overexpression of miR396b in danshen hairy roots inhibited hairy root growth, reduced salvianolic acid concentration, but enhanced tanshinone accumulation, resulting in the biomass and total salvianolic acids respectively reduced to 55.5 and 72.1% of the control and total tanshinones increased up to 1.91-fold of the control. Applied degradome sequencing, 5'RLM-RACE, and qRT-PCR, 13 targets for miR396b were identified including seven conserved SmGRF1-7 and six novel ones. Comparative transcriptomics and microRNomics analysis together with qRT-PCR results confirmed that miR396b targets SmGRFs, SmHDT1, and SmMYB37/4 to mediate the phytohormone, especially gibberellin signaling pathways and consequentially resulted in the phenotype variation of miR396b-OE hairy roots. Furthermore, miR396b could be activated by methyl jasmonate, abscisic acid, gibberellin, salt, and drought stresses. The findings in this study indicated that smi-miR396b acts as an upstream and central regulator in cell growth and the biosynthesis of tanshinones and salvianolic acids, shedding light on the coordinated regulation of plant growth and biosynthesis of active ingredients in S. miltiorrhiza.

Barley microRNAs as metabolic sensors for soil nitrogen availability

Barley (Hordeum vulgare) is one of the most important crops in the world, ranking 4th in the worldwide production. Crop breeders are facing increasing environmental obstacles in the field, such as drought, salinity but also toxic over fertilization which not only impacts quality of the grain but also an yield. One of the most prevalent mechanisms of gene expression regulation in plants is microRNA-mediated silencing of target genes. We identified 13 barley microRNAs and 2 microRNAs* that are nitrogen excess responsive. Four microRNAs respond only in root, eight microRNAs only in shoot and one displays broad response in roots and shoots. We demonstrate that 2 microRNAs* are induced in barley shoot by nitrogen excess. For all microRNAs we identified putative target genes and confirmed microRNA-guided cleavage sites for ten out of thirteen mRNAs. None of the identified microRNAs or their target genes is known as nitrogen excess responsive. Analysis of expression pattern of thirteen target mRNAs and their cognate microRNAs showed expected correlations of their levels. The plant microRNAs analyzed are also known to respond to nitrogen deprivation and exhibit the opposite expression pattern when nitrogen excess/deficiency conditions are compared. Thus, they can be regarded as metabolic sensors of the regulation of nitrogen homeostasis in plants.

Epigenetic Mechanisms in Nematode-Plant Interactions

Epigenetic mechanisms play fundamental roles in regulating numerous biological processes in various developmental and environmental contexts. Three highly interconnected epigenetic control mechanisms, including small noncoding RNAs, DNA methylation, and histone modifications, contribute to the establishment of plant epigenetic profiles. During the past decade, a growing body of experimental work has revealed the intricate, diverse, and dynamic roles that epigenetic modifications play in plant-nematode interactions. In this review, I summarize recent progress regarding the functions of small RNAs in mediating plant responses to infection by cyst and root-knot nematodes, with a focus on the functions of microRNAs. I also recapitulate recent advances in genome-wide DNA methylation analysis and discuss how cyst nematodes induce extensive and dynamic changes in the plant methylome that impact the transcriptional activity of genes and transposable elements. Finally, the potential role of nematode effector proteins in triggering such epigenome changes is discussed.

A role for Arabidopsis growth-regulating factors 1 and 3 in growth-stress antagonism

Growth-regulating factors (GRFs) belong to a small family of transcription factors that are highly conserved in plants. GRFs regulate many developmental processes and plant responses to biotic and abiotic stimuli. Despite the importance of GRFs, a detailed mechanistic understanding of their regulatory functions is still lacking. In this study, we used ChIP sequencing (ChIP-seq) to identify genome-wide binding sites of Arabidopsis GRF1 and GRF3, and correspondingly their direct downstream target genes. RNA-sequencing (RNA-seq) analysis revealed that GRF1 and GRF3 regulate the expression of a significant number of the identified direct targets. The target genes unveiled broad regulatory functions of GRF1 and GRF3 in plant growth and development, phytohormone biosynthesis and signaling, and the cell cycle. Our analyses also revealed that clock core genes and genes with stress- and defense-related functions are most predominant among the GRF1- and GRF3-bound targets, providing insights into a possible role for these transcription factors in mediating growth-defense antagonism and integrating environmental stimuli into developmental programs. Additionally, GRF1 and GRF3 target molecular nodes of growth-defense antagonism and modulate the levels of defense- and development-related hormones in opposite directions. Taken together, our results point to GRF1 and GRF3 as potential key determinants of plant fitness under stress conditions.

MicroRNA miR396, GRF transcription factors and GIF co-regulators: a conserved plant growth regulatory module with potential for breeding and biotechnology

Multicellular life relies on complex regulatory mechanisms ensuring proper growth and development. In plants, these mechanisms construct a body plan that is both reproducible, and highly flexible for adaptation to different environmental conditions. A crucial regulatory module - consisting of microRNA miR396, GROWTH REGULATING FACTORS (GRFs) and GRF-INTERACTING FACTORS (GIFs) - has been shown to control growth of multiple tissues and organs in a variety of species. Especially in the last few years, research has expanded our knowledge of miR396-GRF/GIF function to crops, where it affects agronomically important traits, and highlighted its role in coordinating growth with endogenous and environmental factors. Special properties make the miR396-GRF/GIF system highly efficient in growth regulation and a promising target for improving plant yield.

Conserved miR396b-GRF Regulation Is Involved in Abiotic Stress Responses in Pitaya (Hylocereus polyrhizus)

MicroRNA396 (miR396) is a conserved microRNA family that targets growth-regulating factors (GRFs), which play significant roles in plant growth and stress responses. Available evidence justifies the idea that miR396-targeted GRFs have important functions in many plant species; however, no genome-wide analysis of the pitaya (Hylocereus polyrhizus) miR396 gene has yet been reported. Further, its biological functions remain elusive. To uncover the regulatory roles of miR396 and its targets, the hairpin sequence of pitaya miR396b and the open reading frame (ORF) of its target, HpGRF6, were isolated from pitaya. Phylogenetic analysis showed that the precursor miR396b (MIR396b) gene of plants might be clustered into three major groups, and, generally, a more recent evolutionary relationship in the intra-family has been demonstrated. The sequence analysis indicated that the binding site of hpo-miR396b in HpGRF6 is located at the conserved motif which codes the conserved "RSRKPVE" amino acid in the Trp-Arg-Cys (WRC) region. In addition, degradome sequencing analysis confirmed that four GRFs (GRF1, c56908.graph_c0; GRF4, c52862.graph_c0; GRF6, c39378.graph_c0 and GRF9, c54658.graph_c0) are hpo-miR396b targets that are regulated by specific cleavage at the binding site between the 10th and 11th nucleotides from the 5' terminus of hpo-miR396b. Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that hpo-miR396b is down-regulated when confronted with drought stress (15% polyethylene glycol, PEG), and its expression fluctuates under other abiotic stresses, i.e., low temperature (4 ± 1 °C), high temperature (42 ± 1 °C), NaCl (100 mM), and abscisic acid (ABA; 0.38 mM). Conversely, the expression of HpGRF6 showed the opposite trend to exposure to these abiotic stresses. Taken together, hpo-miR396b plays a regulatory role in the control of HpGRF6, which might influence the abiotic stress response of pitaya. This is the first documentation of this role in pitaya and improves the understanding of the molecular mechanisms underlying the tolerance to drought stress in this fruit.

MicroRNAs, New Players in the Plant-Nematode Interaction

Plant-parasitic root-knot and cyst nematodes are microscopic worms that cause severe damage to crops and induce major agricultural losses worldwide. These parasites penetrate into host roots and induce the formation of specialized feeding structures, which supply the resources required for nematode development. Root-knot nematodes induce the redifferentiation of five to seven root cells into giant multinucleate feeding cells, whereas cyst nematodes induce the formation of a multinucleate syncytium by targeting a single root cell. Transcriptomic analyses have shown that the induction of these feeding cells by nematodes involves an extensive reprogramming of gene expression within the targeted root cells. MicroRNAs are small noncoding RNAs that act as key regulators of gene expression in eukaryotes by inducing the posttranscriptional silencing of protein coding genes, including many genes encoding transcription factors. A number of microRNAs (miRNAs) displaying changes in expression in root cells in response to nematode infection have recently been identified in various plant species. Modules consisting of miRNAs and the transcription factors they target were recently shown to be required for correct feeding site formation. Examples include miR396 and GRF in soybean syncytia and miR159 and MYB33 in Arabidopsis giant cells. Moreover, some conserved miRNA/target modules seem to have similar functions in feeding site formation in different plant species. These miRNAs may be master regulators of the reprogramming of expression occurring during feeding site formation. This review summarizes current knowledge about the role of these plant miRNAs in plant-nematode interactions.