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Polyploid plants often exhibit enhanced stress tolerance. Switchgrass is a perennial rhizomatous bunchgrass that is considered ideal for cultivation in marginal lands, including sites with saline soil. In this study, we investigated the physiological responses and transcriptome changes in the octoploid and tetraploid of switchgrass (Panicum virgatum L. 'Alamo') under salt stress. We found that autoploid 8× switchgrass had enhanced salt tolerance compared with the amphidiploid 4× precursor, as indicated by physiological and phenotypic traits. Octoploids had increased salt tolerance by significant changes to the osmoregulatory and antioxidant systems. The salt-treated 8× Alamo plants showed greater potassium (K+) accumulation and an increase in the K+/Na+ ratio. Root transcriptome analysis for octoploid and tetraploid plants with or without salt stress revealed that 302 upregulated and 546 downregulated differentially expressed genes were enriched in genes involved in plant hormone signal transduction pathways and were specifically associated with the auxin, cytokinin, abscisic acid, and ethylene pathways. Weighted gene co-expression network analysis (WGCNA) detected four significant salt stress-related modules. This study explored the changes in the osmoregulatory system, inorganic ions, antioxidant enzyme system, and the root transcriptome in response to salt stress in 8× and 4× Alamo switchgrass. The results enhance knowledge of the salt tolerance of artificially induced homologous polyploid plants and provide experimental and sequencing data to aid research on the short-term adaptability and breeding of salt-tolerant biofuel plants. [ABSTRACT FROM AUTHOR]

Miscanthus spp. show excellent application prospects due to its bioenergy potential and multiple ecological services. Annual N export with biomass harvest from Miscanthus, even without fertilizer supplement, do not reduce soil N levels. The question arises regarding how Miscanthus can maintain stable soil N levels. Metagenomic strategies were used to reveal soil N‐cycling‐related microbiome and their functional contributions to processes of soil N‐cycling based on the comparison among the bare land, cropland, 10‐year Miscanthus × giganteus, and 15‐year Miscanthus sacchariflorus fields. The results showed that, after long‐term cropland‐to‐Miscanthus conversion (LCMC), 16 of 21 bacterial phyla and all the archaeal phyla exhibited significant changes. Soil microbial denitrification and nitrification functions were significantly weakened, and N fixation (NF) was significantly enhanced. The biosynthesis of amino acids, especially alanine, aspartate, and glutamate metabolism, in soil N‐cycling‐related microbiome was dramatically promoted. The genus Anaeromyxobacter contributed largely to the NF process after LCMC. Variations in the soil available potassium, available N, organic C, and total N contents drove a functional shift of soil microbiome from cropland to Miscanthus pattern. We conclude that Miscanthus can recruit Anaeromyxobacter communities to enhance NF benefiting its biomass sustainability and soil N balance. [ABSTRACT FROM AUTHOR]

Zoysia japonica is an important warm-season turfgrass used worldwide. The decreased aesthetic quality and functionality during leaf senescence hamper its further utilization. However, information about the transcriptional mechanism and genes involved in leaf senescence in Z. japonica needs to be more extensive. Therefore, to better understand leaf senescence in Z. japonica, we investigated the integrated analysis of chlorophyll fluorescence test (JIP-test) and RNA sequencing (RNA-seq) of mature and senescent leaves. First, we identified 22,049 genes, of which 4038 were differentially expressed genes (DEGs). The results for gene expression profiles were evaluated using quantitative real-time PCR. A total of 2515 genes have homologous genes in other plants. The matched known-function SAGs are mainly involved in chlorophyll degradation and plant hormone response. A total of 539 differentially expressed transcription factor genes, including AP2/ERF-ERF, NAC, WRKY, bHLH, and MYB, were identified to be associated with leaf senescence. Next, senescence represses chlorophyll biosynthesis while upregulating chlorophyll degradation. Senescence harms the integrity and functionality of PSII, PSI, and the intersystem electron transport chain. In addition, IAA biosynthesis was inhibited, whereas ABA and ET biosynthesis were activated in leaf senescence, and senescence activates signal transduction of IAA, ABA, and ET. These findings add to our understanding of the regulatory mechanism of leaf senescence. The senescence-associated genes are candidate targets for providing new insight into leaf senescence modeling in Z. japonica. They provided a theoretical foundation to reveal the functions of senescence-associated genes and chlorophyll catabolic genes involved in leaf senescence. [ABSTRACT FROM AUTHOR]

Buffalograss [Buchloe dactyloides (Nutt.) Engelm.] has become the most widely cultivated warm-season turfgrass in northern China because of its low-maintenance requirements. Nitrogen (N) can be applied to plants in a range of formulations. However, preference of nitrogen uptake and the effects of N form on plant growth and nitrogen accumulation has not been established in buffalograss. In this study, we evaluated the effects of different inorganic nitrogen forms (NO3−-N, NH4+-N, and NO3−-N: NH4+-N = 1:1) on growth and nitrogen accumulation in buffalograss seedlings. Results showed that supply of three N forms significantly increased buffalograss seedlings growth, biomass, and N contents of all plant organs compared with the seedlings receiving free nitrogen. Plants achieved better growth performance when they received nitrate as the sole N source, which stimulated stolon growth and increased the biomass of ramets, spacers, and aboveground and total plant biomass, and also allocated more biomass to ramets and more N to spacers. Meanwhile, those plants supplied with the treatment +NH4NO3 displayed a significantly greater N content in the ramet, 15N abundance, and 15N accumulation amount in all organs. These data suggest NO3−-N supplied either singly or in mixture increased vegetative propagation and thus facilitates buffalograss establishment. However, applications of ammonium caused detrimental effects on buffalograss seedlings growth, but +NO3− could alleviate NH4+-induced morphological disorders. Thus, recommendations to increase vegetative propagation and biomass accumulation in buffalograss seedlings should consider increasing NO3−-N in a fertility program and avoiding applications of nitrogen as NH4+-N. [ABSTRACT FROM AUTHOR]

The bioenergy crop switchgrass (Panicum virgatum L.) has been recognized as friendly to the soil of cultivated land depending on the previous land use types and management practices. However, the effects of switchgrass establishment on soil properties at a broader depth when it is harvested annually without any fertilization in northern China largely remain unknown. To explore the impacts of unfertilized switchgrass on soil physical and chemical properties, 0–100 cm soil samples were collected from 7-year cropland-to-switchgrass conversion and the bare land (control). The results showed that switchgrass establishment increased soil total and capillary porosity, CFU numbers of the microbial communities (fungi, bacteria, and actinomycetes), contents of microbial biomass (carbon, nitrogen, and phosphorus), and water-soluble organic carbon, and decreased soil bulk density, mostly at 0–60 cm depths, compared to the control values. Notably, the annual harvest of switchgrass insignificantly increased soil total and available nitrogen contents and slightly reduced available phosphorus and potassium contents. In conclusion, long-term cropland conversion to unfertilized switchgrass could ameliorate soil properties and does not cause soil depletion. The output of this study could inspire governments and farmers to make large-scale use of switchgrass in the ecological restoration of abandoned cropland in north China. [ABSTRACT FROM AUTHOR]

Pennisetum species have importance in foraging, agriculture, energy-production, the environment, and landscaping. To promote the preservation and utilization of ornamental Pennisetum resources, we developed simple sequence repeat (SSR) markers from the Pennisetum setaceum cv. 'Rubrum' transcriptome and verified their conservation in 38 sources. Our transcriptome sequencing efforts generated 58.91 Gb of clean data containing 55,627 unigenes. We functionally annotated 30,930 unigenes, with functions enriched in translation and ribosomal structure and biogenesis. Database comparisons indicated that the closest relative of P. setaceum cv. 'Rubrum' is Setaria italica. Over five thousand SSR markers were detected in the transcriptomic data. We selected 38 pairs of highly polymorphic SSR markers from 50 randomly selected SSR markers. Based on genetic diversity analysis of 38 ornamental Pennisetum sources, we obtained 312 polymorphic bands, with an average of 8.21 alleles per primer. Principal coordinate analyses and generation of a, which proved that Pennisetum has moderate genetic diversity. In addition, fingerprint maps were constructed to improve Pennisetum identification. The transcriptome data generated by our study enhances the transcriptional information available for P. setaceum. This study lays the foundation for the collection and utilization of ornamental Pennisetum resources and provides a basis for future breeding projects using this species. [ABSTRACT FROM AUTHOR]

The degradation of chlorophyll is of great significance to plant growth. The chlorophyll b reductase NOL (NYC1-like) is in charge of catalyzing the degradation of chlorophyll b and maintaining the stability of the photosystem. However, the molecular mechanisms of NOL-mediated chlorophyll degradation, senescence, and photosynthesis and its functions in other metabolic pathways remain unclear, especially in warm-season turfgrass. In this study, ZjNOL was cloned from Zoysia japonica. It is highly expressed in senescent leaves. Subcellular localization investigation showed ZjNOL is localized in the chloroplast and the bimolecular fluorescence complementation (BiFC) results proved ZjNOL interacts with ZjNYC1 in vivo. ZjNOL promoted the accumulation of abscisic acid (ABA) and carbohydrates, and the increase of SAG14 at the transcriptional level. ZjNOL simultaneously led to the excessive accumulation of reactive oxygen species (ROS), the activation of antioxidant enzymes, and the generation of oxidative stress, which in turn accelerated senescence. Chlorophyll fluorescence assay (JIP-test) analysis showed that ZjNOL inhibited photosynthetic efficiency mainly through damage to the oxygen-evolving complex. In total, these results suggest that ZjNOL promotes chlorophyll degradation and senescence and negatively affects the integrity and functionality of the photosystem. It could be a valuable candidate gene for genome editing to cultivate Z. japonica germplasm with prolonged green period and improved photosynthesis efficiency. [ABSTRACT FROM AUTHOR]

The turfgrass species Carex rigescens has broad development and utilization prospects in landscaping construction. However, seed dormancy and a low germination rate have inhibited its application. Furthermore, the molecular mechanisms of seed germination in C. rigescens have not been thoroughly studied. Therefore, in the present study, PacBio full-length transcriptome sequencing combined with Illumina sequencing was employed to elucidate the germination mechanism of C. rigescens seeds under variable temperatures. In general, 156,750 full-length non-chimeric sequences, including those for 62,086 high-quality transcripts, were obtained using single-molecule long read sequencing. In total, 40,810 high-quality non-redundant, 1,675 alternative splicing, 28,393 putative coding sequences, and 1,052 long non-coding RNAs were generated. Based on the newly constructed full-length reference transcriptome, 23,147 differentially expressed genes were identified. We screened four hub genes participating in seed germination using weighted gene co-expression network analysis. Combining these results with the physiological observations, the important roles of sucrose and starch metabolic pathways in germination are further discussed. In conclusion, we report the first full-length transcriptome of C. rigescens , and investigated the physiological and transcriptional mechanisms of seed germination under variable temperatures. Our results provide valuable information for future transcriptional analyses and gene function studies of C. rigescens. [ABSTRACT FROM AUTHOR]

Pheophytinase (PPH), the phytol hydrolase, plays important roles in chlorophyll degradation. Nevertheless, little attention has been paid to the PPHs in warm-season grass species; neither its detailed function in photosynthesis has been systematically explored to date. In this study, we isolated ZjPPH from Zoysia japonica , an excellent warm-season turfgrass species. Quantitative real-time PCR analysis and promoter activity characterization revealed that the expression of ZjPPH could be induced by senescence, ABA, and dark induction. Subcellular localization observation proved that ZjPPH was localized in the chloroplasts. Overexpression of ZjPPH accelerated the chlorophyll degradation and rescued the stay-green phenotype of the Arabidopsis pph mutant. Moreover, ZjPPH promoted senescence with the accumulation of ABA and soluble sugar contents, as well as the increased transcriptional level of SAG12 and SAG14. Transmission electron microscopy investigation revealed that ZjPPH caused the decomposition of chloroplasts ultrastructure in stable transformed Arabidopsis. Furthermore, chlorophyll a fluorescence transient measurement analysis suggested that ZjPPH suppressed photosynthesis efficiency by mainly suppressing both photosystem II (PSII) and photosystem I (PSI). In conclusion, ZjPPH plays an important role in chlorophyll degradation and senescence. It could be a valuable target for genetic editing to cultivate new germplasms with stay-green performance and improved photosynthetic efficiency. [ABSTRACT FROM AUTHOR]

Miscanthus spp. are increasingly cultivated in cropland worldwide due to their bioenergy potential and multiple ecological services. Effects of long‐term cropland‐to‐Miscanthus conversion without N fertilizer on soil microbiome and N cycling largely remain unknown. We aimed to explore the effects of Miscanthus conversion on soil microbiome and N cycling over a 15‐year period. We analyzed diversity, composition, and abundance of bacterial and archaeal communities using 16S rRNA amplicon sequencing, and abundances of N‐cycling‐related genes using quantitative polymerase chain reaction of 0–10 cm soils collected from bare land, cropland, 10‐year Miscanthus × giganteus, and 15‐year Miscanthussacchriflorus land in Beijing. Conversion decreased soil sand and micro‐aggregate proportion, nitrate N (NiN), available phosphorus levels, conductivity, temperature, and pH, while increasing proportion of soil clay and macro‐aggregate (MAA), soil organic C (SOC), available N (AN), exchangeable Mg2+ (EMg2+), and available potassium (AK) contents as well as microbial C/N. Consequently, diversity, composition, and abundance of soil bacterial community exhibited larger changes than those values of archaeal community after conversion. Soil AP, EMg2+, AK, and SOC were key factors in shifting microbiome from the cropland to Miscanthus pattern. Moreover, abundances of bacterial and archaeal communities and the N fixer gene nifH increased, whereas that of the bacterial ammonia monooxygenase gene decreased. The copies of other N‐cycling‐related genes in the two Miscanthus lands seemed similar to those values of cropland. The nifH copies negatively correlated with soil NiN and positively correlated with AN, EMg2+, ECa2+, SOC, AK, and MAA. We conclude that changes in soil microbiome pattern induced by the variation of soil properties enhance microbial N fixation potential, maintaining stable N levels and robust N cycling with lower N leakage risk after conversion. These results should inspire farmers and governments to large‐scale use Miscanthus on marginal cropland in Northern China. [ABSTRACT FROM AUTHOR]

Switchgrass is a photoperiod-sensitive energy grass suitable for growing in the marginal lands of China. We explored the effects of extended photoperiods of low-irradiance light (7 μmol·m-2·s-1, no effective photosynthesis) on the growth, the biomass dry weight, the biomass allocation, and, especially, the stem digestibility and cell wall characteristics of switchgrass. Two extended photoperiods (i.e., 18 and 24 h) were applied over Alamo. Extended light exposure (18 and 24 h) resulted in delayed heading and higher dry weights of vegetative organs (by 32.87 and 35.94%, respectively) at the expense of reducing the amount of sexual organs (by 40.05 and 50.87%, respectively). Compared to the control group (i.e., natural photoperiod), the yield of hexoses (% dry matter) in the stems after a direct enzymatic hydrolysis (DEH) treatment significantly increased (by 44.02 and 46.10%) for those groups irradiated during 18 and 24 h, respectively. Moreover, the yield of hexoses obtained via enzymatic hydrolysis increased after both basic (1% NaOH) and acid (1% H2SO4) pretreatments for the groups irradiated during 18 and 24 h. Additionally, low-irradiance light extension (LILE) significantly increased the content of non-structural carbohydrates (NSCs) while notably reducing the lignin content and the syringyl to guaiacyl (S/G) ratio. These structural changes were in part responsible for the observed improved stem digestibility. Remarkably, LILE significantly decreased the cellulose crystallinity index (CrI) of switchgrass by significantly increasing both the arabinose substitution degree in xylan and the content of ammonium oxalate-extractable uronic acids, both favoring cellulose digestibility. Despite this LILE technology is not applied to the cultivation of switchgrass on a large scale yet, we believe that the present work is important in that it reveals important relationships between extended day length irradiations and biomass production and quality. Additionally, this study paves the way for improving biomass production and digestibility via genetic modification of day length sensitive transcription factors or key structural genes in switchgrass leaves. [ABSTRACT FROM AUTHOR]

In this study, tassels of Cave-in-Rock (upland) and Alamo (lowland) were removed at or near tassel emergence to explore its effects on biomass production and quality. Tassel-removed (TR) Cave-in-Rock and Alamo both exhibited a significant (P<0.05) increase in plant heights (not including tassel length), tiller number, and aboveground biomass dry weight (10% and 12%, 30% and 13%, 13% and 18%, respectively by variety) compared to a control (CK) treatment. Notably, total sugar yields of TR Cave-in-Rock and Alamo stems increased significantly (P<0.05 or 0.01) by 19% and 19%, 21% and 14%, 52% and 18%, respectively by variety, compared to those of control switchgrass under 3 treatments by direct enzymatic hydrolysis (DEH), enzymatic hydrolysis after 1% NaOH pretreatment (EHAL) and enzymatic hydrolysis after 1% H2SO4 pretreatment (EHAC). These differences were mainly due to significantly (P<0.05 or 0.01) higher cellulose content, lower cellulose crystallinity indexes (CrI) caused by higher arabinose (Ara) substitution in xylans, and lower S/G ratio in lignin. However, the increases of nitrogen (N) and sulphur (S) concentration negatively affects the combustion quality of switchgrass aboveground biomass. This work provides information for increasing biomass production and quality in switchgrass and also facilitates the inhibition of gene dispersal of switchgrass in China. [ABSTRACT FROM AUTHOR]

Abstract: Crop productivity is greatly affected by soil salinity, so improvement in salinity tolerance of crops is a major objective of many studies. We overexpressed the Arabidopsis thaliana SOS1 gene, which encodes a plasma membrane Na+/H+ antiporter, in tobacco (Nicotiana tabacum cv. Xanthi-nc). Compared with nontransgenic plants, seeds from transgenic tobacco had better germination under 120mM (mmolL−1) NaCl stress; chlorophyll loss in the transgenic seedlings treated with 360mM NaCl was less; transgenic tobacco showed superior growth after irrigation with NaCl solutions; and transgenic seedlings with 150mM NaCl stress accumulated less Na+ and more K+. In addition, roots of SOS1-overexpressing seedlings lost less K+ instantaneously in response to 50mM NaCl than control plants. These results showed that the A. thaliana SOS1 gene potentially can improve the salt tolerance of other plant species. [Copyright &y& Elsevier]

Abstract: Drought is a major environmental stress factor that affects growth and development of plants. Abscisic acid (ABA), osmotically active compounds, and synthesis of specific proteins, such as proteins that scavenge oxygen radicals, are crucial for plants to adapt to water deficit. LOS5/ABA3 (LOS5) encodes molybdenum-cofactor sulfurase, which is a key regulator of ABA biosynthesis. We overexpressed LOS5 in tobacco using Agrobacterium-mediated transformation. Detached leaves of LOS5-overexpressing seedlings showed lower transpirational water loss than that of nontransgenic seedlings in the same period under normal conditions. When subjected to water-deficit stress, transgenic plants showed less wilting, maintained higher water content and better cellular membrane integrity, accumulated higher quantities of ABA and proline, and exhibited higher activities of antioxidant enzymes, i.e., superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, as compared with control plants. Furthermore, LOS5-overexpressing plants treated with 30% polyethylene glycol showed similar performance in cellular membrane protection, ABA and proline accumulation, and activities of catalase and peroxidase to those under drought stress. Thus, overexpression of LOS5 in transgenic tobacco can enhance drought tolerance. [Copyright &y& Elsevier]

Polyploidization is regularly regarded as an important tool for the generation of innovative germplasm resources and plant breeding. In this study, autopolyploid switchgrass lines were produced from calli derived from immature inflorescence of tetraploid switchgrass ( Panicum virgatum L.), both lowland cv. Alamo and Kanlow, and upland cv. Ranlow, through colchicine treatments. Ploidy levels of plantlets regenerated from the calli were screened by flow cytometry. Growth characteristics of the tetraploid and octoploid switchgrass cultivars were further investigated in a field experiment. Compared with the tetraploid plants of the three switchgrass cultivars, the corresponding octoploid plants showed significant reduction in plant height, number of tillers per plant and fresh matter, but an increase in leaf length and width. [ABSTRACT FROM AUTHOR]