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Nanotechnology is one of the promising techniques and shares wide ranges of applications almost in every field of life. Nanomaterials are getting continuous attractions due to specific physical and chemical properties and being applied as multifunctional material. The use of nanomaterials/nanoparticles in agriculture sector for crop improvement and protection against various environmental threats have attained greater significance. Size and nature of nanoparticles, mode of application, environmental conditions, rhizospheric and phyllospheric environment, and plant species are major factors that influence the action of nanoparticles. The mode or method of nanoparticle applications to plants is attaining greater attentions. Recently, different methods for nanoparticle applications (seed priming, foliar, and root application) are being used to improve crop growth. It is of quite worth that which method is suitable for nanoparticle application, and how nanoparticles can possibly translocate to various plant tissues from root to shoot or vice versa. These information's are poorly understood and need more investigations to explore the comprehensive mechanism by which nanoparticles make their possible entry through different plant organs and how they transport to regulate various physiological and molecular functions in plant cells. Therefore, this study comprehensively provides the knowledge of nanoparticles uptake via seed priming, foliar exposure, and root application, and their possible translocation mechanism within plants influenced by various factors that has not clearly presented. This study will provide new insights to find out an actual uptake and translocation mechanism of nanoparticles that may help researchers to develop nanoparticle-based new strategies for plants to cope with various environmental challenges. This study also focuses on different soil factors or above ground factors that are involved in nanoparticles uptake and translocation and ultimately their functioning in plants.

Orchardgrass (Dactylis glomerata L.) is an important forage grass for cultivating livestock worldwide. Here, we report an similar to 1.84-Gb chromosome-scale diploid genome assembly of orchardgrass, with a contig N50 of 0.93 Mb, a scaffold N50 of 6.08 Mb and a super-scaffold N50 of 252.52 Mb, which is the first chromosome-scale assembled genome of a cool-season forage grass. The genome includes 40 088 protein-coding genes, and 69% of the assembled sequences are transposable elements, with long terminal repeats (LTRs) being the most abundant. The LTRretrotransposons may have been activated and expanded in the grass genome in response to environmental changes during the Pleistocene between 0 and 1 million years ago. Phylogenetic analysis reveals that orchardgrass diverged after rice but before three Triticeae species, and evolutionarily conserved chromosomes were detected by analysing ancient chromosome rearrangements in these grass species. We also resequenced the whole genome of 76 orchardgrass accessions and found that germplasm from Northern Europe and East Asia clustered together, likely due to the exchange of plants along the 'Silk Road' or other ancient trade routes connecting the East and West. Last, a combined transcriptome, quantitative genetic and bulk segregant analysis provided insights into the genetic network regulating flowering time in orchardgrass and revealed four main candidate genes controlling this trait. This chromosome-scale genome and the online database of orchardgrass developed here will facilitate the discovery of genes controlling agronomically important traits, stimulate genetic improvement of and functional genetic research on orchardgrass and provide comparative genetic resources for other forage grasses. National Basic Research Program (973 Program) in ChinaNational Basic Research Program of China [2014CB138705]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China [NSFC 31872997]; Earmarked Fund for Modern Agro-industry Technology Research System [CARS-34]; National Project on Sci-Tec Foundation Resources Survey [2017FY100602] This research work was funded by the National Basic Research Program (973 Program) in China (No. 2014CB138705), the National Natural Science Foundation of China (NSFC 31872997), the Earmarked Fund for Modern Agro-industry Technology Research System (No. CARS-34) and the National Project on Sci-Tec Foundation Resources Survey (2017FY100602). Public domain – authored by a U.S. government employee

As an important part of modular multilevel converter (MMC), the reactor at the bridge arm of the converter is an essential component in its topology. During the operation of MMC, because the capacitor voltage on each phase bridge arm is not equal, it is easy to cause the unbalanced voltage of bridge arm, and finally lead to the unequal DC current component in the three-phase bridge arm. The unbalance of DC component can easily lead to excessive magnetic bias of one phase in three-phase reactor, and then cause the unbalance of AC component in three-phase bridge arm, and finally lead to zero sequence circulating current inside the bridge arm. The zero sequence circulating current enters the DC side and intensifies the fluctuation of voltage, current and power at DC side. In this paper, the finite element method is used to simulate and analyze the suppression effect of three-phase bridge arm reactor on the second harmonic circulating current under the condition of unbalanced DC component, which provides a theoretical basis for the design and selection of MMC bridge arm reactor.

Awns, which are either bristles or hair-like outgrowths of lemmas in the florets, are one of the typical morphological characteristics of grass species. These stiff structures contribute to grain dispersal and burial and fend off animal predators. However, their phenotypic and genetic associations with traits deciding potential yield and quality are not fully understood. Awns appear to improve photosynthesis, provide assimilates for grain filling, thus contributing to the final grain yield, especially under temperature- and water-stress conditions. Long awns, however, represent a competing sink with developing kernels for photosynthates, which can reduce grain yield under favorable conditions. In addition, long awns can hamper postharvest handling, storage, and processing activities. Overall, little is known about the elusive role of awns, thus, this review summarizes what is known about the effect of awns on grain yield and biomass yield, grain nutritional value, and forage-quality attributes. The influence of awns on the agronomic performance of grasses seems to be associated with environmental and genetic factors and varies in different stages of plant development. The contribution of awns to yield traits and quality features previously documented in major cereal crops, such as rice, barley, and wheat, emphasizes that awns can be targeted for yield and quality improvement and may advance research aimed at identifying the phenotypic effects of morphological traits in grasses.

Cyclic lateral loading tests were conducted on six composite plate shear walls–concrete encased and two conventionally reinforced concrete walls. The composite plate shear walls–concrete encased were constructed using high-performance concrete and different steel configurations with a same steel content ratio. These walls were divided into two batches. Three composite plate shear walls–concrete encased and one conventional wall were first exposed to the ISO 834 standard fire before the cyclic tests. To their comparison, the other four walls were only tested under the cyclic loading at room temperature. During the fire tests, the four walls experienced the spalling of concrete. The composite plate shear walls–concrete encased suffered more explosive spalling than the conventional wall. After the fire tests, all walls were tested under the cyclic loading. Based on the test results, analysis and discussions were made on the lateral load, lateral stiffness, and energy dissipation ability of walls. The difference was identified between the behavior of composite plate shear walls–concrete encased and that of conventional wall. Moreover, the influences of fire exposure were analyzed on seismic behavior of shear walls. Generally, the high temperatures reduce the yield, peak, and ultimate loads of walls and degrade the lateral stiffness. No significant difference can be found in energy dissipation ability between the heated and unheated walls before the drift ratio 1/120.

Awns, needle-like structures formed on the distal of the lemmas in the florets, are of interest because of their essential roles in seed dispersal, germination and photosynthesis. Previous research has reported the potential benefits of awns in major cereal grasses, yet reports on the agronomic and economic implications of awn length variation in forage grasses remain scarce. This study investigated the variation of awn length among 20 Siberian wildrye populations and the effect of awn length on seed yield and yield components. This work then studied the impact of awn length on seed dispersal and germination. The analyses indicated a high level of awn length variation among populations. Awn length showed a significant influence on harvested seed yield per plant (p &lt, 0.05) mostly driven by interactions between awn length and the majority of seed yield components. Principal component analysis clearly revealed that the final impact of awn length on seed yield depends on the balance of its positive and negative effects on traits determining seed yield. Furthermore, awn length tended to increase seed dispersal distance, although little diversity in the nature of this progression was observed in some populations. Awn length exhibited a significant relationship (p &lt, 0.05) with germination percentage. It also tended to shorten germination duration, although this interaction was not statistically significant. Collectively, these results provide vital information for breeding and agronomic programs aiming to maintain yield in grasses. This is the first report to demonstrate in Siberian wildrye the agronomic impacts of awn length variation.

The fast DC vacuum circuit breaker is required that the vacuum interrupter can not only break large current within several milliseconds, but also guarantee the required mechanical life under the condition that the mechanical impact is much larger than that of the AC vacuum interrupter. This paper investigates the DC breaking capability of three typical vacuum interrupters with axial magnetic field contact structure-without slots, with radial slots and with parallel slots by simulation. And the current breaking capability of contacts without slots is proved by prototype test. A test circuit and a method for current breaking capability of fast switchgears are proposed. The research results can provide technical reference for the engineering application of fast DC vacuum switchgears.

Dear Editor,Arbuscular mycorrhizal fungi(AMF)belonging to phylum Glomeromycota, form symbiotic associations with roots of over 80% of land plant species in terrestrial ecosystems(van der Heijden et al., 2015).A growing body of evidence shows that symbiotic AMF are important for plant growth and health(van der Heijden et al., 2015).A plant root is commonly associated with a complex AMF community in terrestrial ecosystems(Pivato et al., 2007; Davison et al., 2015;Mao et al., 2015).The diversity and composition of AMF in the roots of several model plants(Pivato et al., 2007)and crops(Mao et al., 2015)has been widely studied.The host plant is a key factor affecting the root-associated AMF community(RAMFC), and studies found that the effects of host plants on RAFMC could be operating on the levels of different species(Pivato et al., 2007), cultivars(Mao et al.,2015)and plant genotype(An et al., 2010).Elymus sibiricus is one of the most commonly distributed cool-season perennial grasses found in temperate regions and is becoming increasingly important as a forage grass to providing good quality forage for livestock(Chen and Jia, 2002).Some studies had been focused on the symbiotic association between forage plants in Elymus and AMF(Liu et al., 2012;Chu et al., 2016), and the presence of AMF in roots appears likely to improve the resistance of E.nutans to cold stress(Chu et al., 2016)and increase the biomass of this grass species(Yang et al., 2018).The present study was conducted to investigate, using sequencing technology, the potential host effects of E.sibiricus populations on the diversity of their RAMFC.

The identification of biological mechanisms underlying the development of complex quantitative traits, including those that contribute to plant architecture, yield and quality potential, and seed dispersal, is a major focus in the evolutionary biology and plant breeding. The awn, a bristle-like extension from the lemma in the floret, is one of the distinct morphological and physiological traits in grass species. Awns are taught as an evolutionary trait assisting seed dispersal and germination and increasing photosynthesis. Awn development seems to be complex process, involving dramatic phenotypic and molecular changes. Although recent advances investigated the underlying morphological and molecular genetic factors of awn development, there is little agreement about how these factors interact during awn formation and how this interaction affects variation of awn morphology. Consequently, the developmental sequence of the awn is not yet well understood. Here, we review awn morphological and histological features, awn development pathways, and molecular processes of awn development. We argue that morphological and molecular genetic mechanisms of awn development previously studied in major cereal crops, such as barley, wheat, and rice, offered intriguing insights helping to characterize this process in a comparative approach. Applying such an approach will aid to deeply understand factors involved in awn development in grass species.

Elymus sibiricus, which is a perennial and self-pollinated grass, is the typical species of the genus Elymus, which plays an important role in forage production and ecological restoration. No reports have, so far, systematically described the selection of optimal reference genes for reverse transcriptase quantitative real-time polymerase chain reaction (RT-qPCR) analysis in E. sibiricus. The goals of this study were to evaluate the expression stability of 13 candidate reference genes in different experimental conditions, and to determine the appropriate reference genes for gene expression analysis in E. sibiricus. Five methods including Delta Ct (&Delta, Ct), BestKeeper, NormFinder, geNorm, and RefFinder were used to assess the expression stability of 13 potential reference genes. The results of the RefFinder analysis showed that TBP2 and HIS3 were the most stable reference genes in different genotypes. TUA2 and PP2A had the most stable expression in different developmental stages. TBP2 and PP2A were suitable reference genes in different tissues. Under salt stress, ACT2 and TBP2 were identified as the most stable reference genes. ACT2 and TUA2 showed the most stability under heat stress. For cold stress, PP2A and ACT2 presented the highest degree of expression stability. DNAJ and U2AF were considered as the most stable reference genes under osmotic stress. The optimal reference genes were selected to investigate the expression pattern of target gene CSLE6 in different conditions. This study provides suitable reference genes for further gene expression analysis using RT-qPCR in E. sibiricus.

Background Elymus nutans and E. sibiricus are two important forage grasses of the genus Elymus. But they are difficult to grow for commercial seed production due to serious seed shattering. We conducted a comparative transcriptome analysis of abscission zone to find possible transcription changes associated with seed shattering, explore candidate genes involved in seed shattering and identify candidate gene-based EST-SSR markers for germplasm evaluation. Results cDNA libraries from abscission zone (AZ) and non-abscission zone (NAZ) tissues of E. nutans were constructed and sequenced. A total of 111,667 unigenes were annotated and 7644 differentially expressed transcripts (DETs) were predicted, corresponding to 6936 up-regulated in AZ and 708 down-regulated in NAZ. We identified 489 candidate genes related to transcription factor, cell wall hydrolysis or modification, hydrolase activity, phytohormone signaling and response, lignin biosynthesis, and signal transduction or protein turnover. Eleven similar candidate genes involved in polygalacturonase activity, hydrolase activity, and mitogen-activated protein kinase were up-regulated in the abscission zone of the two Elymus species, suggesting these genes may have specific function for abscission zone development and seed shattering. A total of 67 polymorphic EST-SSR markers were developed and characterized based on the sequences of these candidate genes. Fourteen polymorphic EST-SSR primers were finally used to study genetic diversity in 48 E. nutans genotypes with contrasting seed shattering habit. The dendrogram based on molecular data showed that most accessions with similar seed shattering degree tended to group together. Conclusions The expression data generated from this study provides an important resource for future molecular biological research. Many DETs were associated with abscission zone development, and EST-SSR loci related to candidate genes may have potential application in identifying trait-associated markers in E. nutans in the future. Electronic supplementary material The online version of this article (10.1186/s12870-019-1691-4) contains supplementary material, which is available to authorized users.

Additional file 6: Figure S3. Heat map of linkage map.

Figure S1. KEGG classification results of differentially expressed transcripts (DETs) found in E. nutans (A) and E. sibiricus (B). (PDF 214 kb)

Campeiostachys nutans (Griseb.) J. L. Yang, B. R. Baum et C. Yen is a widely cultivated grass that is used for forage. Considering its limited genomic resources, there is a strong need to increase the available data on this species, which would allow for the identification of genes useful for molecular breeding and lead to increased crop quality and productivity. Complementary DNA (cDNA) samples from 11 different tissues were sequenced using Illumina paired-end sequencing. A total of 106,220 unigenes were obtained via de novo assembly, and 82,863 (78.01%) unigenes were annotated based on similarity searches using known proteins. In addition, 8727 expressed sequence tag-simple-sequence repeat (EST-SSR) loci were identified. A subset of 480 EST-SSRs was randomly synthesized and screened for validation across a panel of 16 C. nutans accessions using 48 individual plants, with 113 polymorphic EST-SSRs generating 439 alleles. The number of alleles, observed heterozygosity, expected heterozygosity, and polymorphism information content ranged from three to nine, 0.00 to 1.00, 0.51 to 0.84, and 0.39 to 0.82, respectively. Overall, the C. nutans transcriptomic sequences generated in this study provide both an important platform that will facilitate gene discovery for functional genomic studies and EST-SSR markers for use in breeding.

The basic leucine zipper (bZIP) transcription factors have been shown to play great roles in pathogen defense, light and stress signalling, seed maturation and flower development in plants. However, no reports about this transcription factor family have been reported in grass species, including the model dicotyledonous grass species Medicago truncatula. In the present study, we have identified 75 bZIP transcription factor-encoding genes in the M. truncatula genome. The phylogenetic analysis of these bZIP protein sequences permits classification of them into 12 groups. The chromosome distribution analyses suggesting that bZIP genes in M. truncatula are not recently generated by gene duplication. The results of the identification of intron/exon structural and conserved motifs showed that there is a high group-specificity in all MtbZIP genes. Expression of bZIP transcription factor-encoding genes indicates specific or coexpression patterns of MtbZIP genes involved in organ development, drought-responses and salt-responses. In addition, 104 SSRs specific to 53 MtbZIP genes were detected and 97 primer pairs were developed. The validation of 30 randomly selected primer pairs in 20 alfalfa cultivars showed 17 of them were true-to-type SSR loci and highly transferable among alfalfa cultivars. These results will be important for further cloning and functional characterization of bZIP transcription factors in M. truncatula.

Elymus sibiricus is a perennial, self-pollinating, allotetraploid grass native to northern Asia. It is widely used in cultivated pastures and natural grassland due to excellent cold and drought tolerance, good forage quality, and adaptability to a variety of habitats. Information on the genetic diversity and variation among worldwide E. sibiricus germplasm is limited but necessary for germplasm collection, conservation and effective commercial use. In this study we ana lyzed genetic diversity and variation of 69 E. sibiricus accessions from the species range and constructed DNA fingerprinting profiles of 24 accessions using SCoT markers. A total of 173 bands were generated from 16 SCoT primers, 154 of which were polymorphic with 89.0% of polymorphic bands (PPB) occurring at the species level. The PPB within 8 geographical regions ranged from 2.3 to 54.3 %. Genetic variation was greater within geographical regions (57.9%) than between regions (42.1%). The 24 accessions from Qinghai-Tibet Plateau, Mongolia Plateau, Kazakhstan, and Russia were distinguished by their unique fingerprinting. This is the first report using SCoT markers for identifying cultivars and accessions of E. sibiricus. The DNA fingerprinting profiles of E. sibiricus were useful in germplasm collection and identification. The genetic diversity of worldwide E. sibiricus germplasm has been substantially affected by ecogeographical factors. Our results suggest that collecting and evaluating E. sibiricus germplasm from major geographic regions and unique environments broadens the available genetic base and illustrates the range of variation.

Elymus nutans and Elymus sibiricus are two important perennial forage grasses of the genus Elymus, widely distributed in high altitude regions of Western and Northern China, especially on the Qinghai-Tibetan Plateau. Information on phenotypic and genetic diversity is limited, but necessary for Elymus germplasm collection, conservation, and utilization. In the present study, the phenotypic and genetic differentiation of 73 accessions of the two species were evaluated using 15 phenotypic traits and 40 expressed sequence tag derived simple sequence repeat markers (EST-SSRs). The results showed that only 7.23% phenotypic differentiation (Pst) existed between the two Elymus species based on fifteen quantitative traits. Principal component analysis (PCA) revealed that leaf traits, spike traits, and some seed traits were dominant factors in phenotypic variation. Moreover, 396 (97.8%) and 331 (87.1%) polymorphic bands were generated from 40 EST-SSR primers, suggesting high levels of genetic diversity for the two species. The highest genetic diversity was found in the Northeastern Qinghai-Tibetan Plateau groups. Clustering analysis based on molecular data showed that most accessions of each Elymus species tended to group together. Similar results were described by principal coordinates analysis (PCoA) and structure analysis. The molecular variance analysis (AMOVA) revealed that 81.47% and 89.32% variation existed within the geographical groups for the two species, respectively. Pearson’s correlation analyses showed a strong positive correlation between Nei’s genetic diversity and annual mean temperature. These results could facilitate Elymus germplasm collection, conservation, and future breeding.

Siberian wild rye (Elymus sibiricus L.) is an important native grass in Qinghai-Tibet Plateau of China. The genetic diversity within and among 24 E. sibiricus accessions, cultivars and breeding lines were analyzed using EST-SSR markers. In total, 160 bands were generated from 30 EST-SSR markers, 143 bands of which were polymorphic with the percentage of polymorphic loci (PPB) of 89.4% at the species level. The PPB within accessions ranged from 2.5 to 56.3%, indicating high level of genetic diversity consistent with the variability observed in seed shattering (21.3–56.1%). Larger genetic variation was found within accessions (52.0%) and geographical regions (73.3%) compared to between accessions and regions. These results will facilitate germplasm collection, conservation and future genetic improvement for this species.

The seed dispersion caused by pod shattering is a form of propagation used by many wild species. Loss of seeds from pod shattering is frequent in the common vetch (Vicia sativa L.), an important self-pollinating annual forage legume. However, pod shattering is one of the most important defects that limits the reproduction of the vetch in the field and the usage as a leguminous forage crop. To better understand the vetch pod shattering mechanism, we used high-throughput RNA sequencing to assess the global changes in the transcriptomes of the pod ventral sutures of shattering-susceptible and shattering-resistant vetch accessions screened from 541 vetch germplasms. A total of 1,285 significantly differentially expressed unigenes (DEGs) were detected, including 575 up-regulated unigenes and 710 down-regulated unigenes. Analyses of Gene Ontology and KEGG metabolic enrichment pathways of 1,285 DEGs indicated that 22 DEGs encoding cell wall modifications and hydrolases associated with pod shattering were highly expressed in shattering-susceptible accessions. These genes were mainly enriched in “hydrolase activity,” “cytoplasm,” and “carbohydrate metabolic process” systems. These cell wall modifications and hydrolases genes included β-glucosidase and endo-polygalacturonase, which work together to break down the glycosidic bonds of pectin and cellulose, and to promote the dissolution and disappearance of the cell wall in the ventral suture of the pod and make the pod more susceptible to shattering. We demonstrated the differences in gene transcription levels between the shattering-susceptible and shattering-resistant vetch accessions for the first time and our results provided valuable information for the identifying and characterizing of pod shattering regulation networks in vetch. This information may facilitate the future identification of pod shattering-related genes and their underlying molecular mechanisms in the common vetch.

Elymus sibiricus (siberian wildrye) is a perennial, cool-season, self-pollinating, and allotetraploid grass. As an economically important species, it has been widely grown and used for pasture and hay in northern China. Because of serious seed shattering, however, E. sibiricus is difficult to grow for commercial seed production. To better understand the underlying mechanism of seed shattering, we investigated the differences in seed shattering of cultivars and wild accessions in relation to morphological and genetic diversity, histological characteristics, lignin staining, cell wall hydrolytic enzymes activity and candidate genes expressions. We found high level of morphological and genetic diversity among E. sibiricus accessions. In general, cultivars had higher average pedicel breaking tensile strength (BTS) value than wild accessions, of which PI655199 had the highest average BTS value (144.51 gf) and LQ04 had the lowest average BTS value (47.17 gf) during seed development. Seed shattering showed a significant correlation with seed length (SL), awn length (AL) and 1000-seed weight (KW). Seed shattering was caused by degradation of abscission layers that formed at early heading stage, and degradation of abscission layers occurred at 14 days after heading (DAH). Histological analysis of abscission zone showed a smooth fracture surface on the rachilla in high seed shattering genotype, suggesting higher degradation degree of abscission layers. This may resulted from the increased cellulase (CE) and polygalacturonase (PG) activity found in abscission zone at seed physiological maturity. Staining of pedicels of two contrasting genotypes suggested more lignin deposition in low seed shattering genotype may play an role in resistance of seed shattering. Furthermore, candidate genes that involved in cell wall-degrading enzyme and lignin biosynthesis were differentially expressed in abscission zone, indicating the involvement and role in seed shattering. This study provided novel insights into the mechanism of seed shattering in E. sibiricus.

Orchardgrass (Dactylis glomerata L.) is a high quality forage grass naturalized to temperate climates. Used extensively in hay and grazing agriculture, hundreds of orchardgrass cultivars have been released over the past 50 years. However, progress in yield and other agronomic characteristics in orchardgrass cultivars has occurred slowly and often inconsistently. One cause of the slow progress could be a lack of genetic diversity among orchardgrass cultivars, or an over-abundance of diversity within cultivars. With an emphasis on North American cultivars, this study assessed the genetic diversity within and among 52 orchardgrass cultivars, breeding lines and accessions. Genetic similarity within cultivars ranged from 52 to 71%, similar to values from wild-land, unselected accessions. Populations from Wisconsin and Missouri breeding efforts that resulted from two cycles of genotypic recurrent selection were included as checks. Neither group of selection populations exhibited more within-population similarity compared to the wild-land accessions (ecotypes) and cultivars. Genetic differentiation was detected only for the selection populations and several cultivars and breeding lines that had a tendency to originate from eastern Asian germplasm and have late flowering times. These results indicated an abundance of genetic variation within the orchardgrass cultivars, but a paucity of genetic differentiation among cultivars.

GO classification results of differentially expressed transcripts (DETs) found in three DETs sets. The genes were assigned to three main categories: cellular component, molecular function and biological process. The right-hand y-axis indicates the number of annotated genes. The left-hand y-axis indicates the percentage of annotated genes. (PDF 617Â kb)

Differentially expressed transcripts involved in plant hormone signal transduction pathway. Green means that the DETs were down regulated, red represents up regulated, and blue indicates that genes were of mixed expression patterns in the low seed shattering genotype compared to the high seed shattering genotype. The diagram of network was cited from KEGG website. (PDF 176Â kb)

KEGG classification results of differentially expressed transcripts (DETs) found in three DETs sets. All DETs were assigned to five categories: cellular process, environmental information processing, genetic information processing, metabolism and organismal systems. (PDF 182Â kb)