AsHSP26.2, a creeping bentgrass chloroplast small heat shock protein positively regulates plant development

KEY MESSAGE

The creeping bentgrass small heat shock protein AsHSP26.2 positively regulates plant growth and is a novel candidate for use in crop genetic engineering for enhanced biomass production and grain yield. Small heat shock proteins (sHSPs), a family of proteins with high level of diversity, significantly influence plant stress tolerance and plant development. We have cloned a creeping bentgrass chloroplast-localized sHSP gene, AsHSP26.2 responsive to IAA, GA and 6-BA stimulation. Transgenic creeping bentgrass overexpressing AsHSP26.2 exhibited significantly enhanced plant growth with increased stolon number and length as well as enlarged leaf blade width and leaf sheath diameters, but inhibited leaf trichomes initiation and development in the abaxial epidermis. These phenotypes are completely opposite to those displayed in the transgenic plants overexpressing AsHSP26.8, another chloroplast sHSP26 isoform that contains additional seven amino acids (AEGQGDG) between the consensus regions III and IV (Sun et al., Plant Cell Environ 44:1769-1787, 2021). Furthermore, AsHSP26.2 overexpression altered phytohormone biosynthesis and signaling transduction, resulting in elevated auxin and gibberellins (GA) accumulation. The results obtained provide novel insights implicating the sHSPs in plant growth and development regulation, and strongly suggest AsHSP26.2 to be a novel candidate for use in crop genetic engineering for enhanced plant biomass production and grain yield.

Genome Resources for Four Clarireedia Species Causing Dollar Spot on Diverse Turfgrasses

Dollar spot (DS) is a destructive fungal disease impacting almost all warm- and cool-season turfgrasses worldwide. Multiple fungal species in the genus Clarireedia are causal agents of DS. Here, we present whole-genome assemblies of nine fungal isolates in the genus Clarireedia, including four species (C. paspali, C. hainanense, C. jacksonii, and C. monteithiana) causing DS on seashore paspalum (Paspalum vaginatum Sw.), creeping bentgrass (Agrostis stolonifera L.), and Kentucky bluegrass (Poa pratensis L.) in China. This work provides valuable baseline genomic data to support further research and management of DS pathogens on turfgrasses.

Expression of a Chlorophyll b Reductase Gene from Zoysia japonica Causes Changes in Leaf Color and Chlorophyll Morphology in Agrostis stolonifera

The NYC-like (NOL) enzyme is considered as an essential enzyme for chlorophyll b degradation, which catalyzes the formation of 7-hydroxymethyl chlorophyll a from chlorophyll b. The ZjNOL gene was cloned from Zoysia japonica with a completed coding sequence of 981-bp in length, encoding 326 amino acids. ZjNOL was localized on the stroma side of the thylakoid membrane, and co-localized with ZjNYC in the chloroplasts. Multiple photoregulatory elements and hormone regulatory elements were identified in the promoter region of the ZjNOL gene, and the expression level of the ZjNOL gene was dramatically up-regulated in senescence leaves, which were regulated by a variety of plant hormones. ZjNOL's ectopic expression in creeping bentgrass produced yellow leaves, thicker cortex, and smaller vascular column cells. Additionally, transgenic plants exhibited morphological alterations in their chloroplast structure, and the number of grana and thylakoids per grana stack reduced dramatically. Transgenic plants also had a lower photosynthetic rate and Fm/Fv than the control. The transgenic plants displayed a decreased chlorophyll content and a greater rate of ion leakage. The properties and activities of ZjNOL will serve as a foundation for future research into gene functions and regulatory processes.

Functional annotation of creeping bentgrass protein sequences based on convolutional neural network

BACKGROUND

Creeping bentgrass (Agrostis soionifera) is a perennial grass of Gramineae, belonging to cold season turfgrass, but has poor disease resistance. Up to now, little is known about the induced systemic resistance (ISR) mechanism, especially the relevant functional proteins, which is important to disease resistance of turfgrass. Achieving more information of proteins of infected creeping bentgrass is helpful to understand the ISR mechanism.

RESULTS

With BDO treatment, creeping bentgrass seedlings were grown, and the ISR response was induced by infecting Rhizoctonia solani. High-quality protein sequences of creeping bentgrass seedlings were obtained. Some of protein sequences were functionally annotated according to the database alignment while a large part of the obtained protein sequences was left non-annotated. To treat the non-annotated sequences, a prediction model based on convolutional neural network was established with the dataset from Uniport database in three domains to acquire good performance, especially the higher false positive control rate. With established model, the non-annotated protein sequences of creeping bentgrass were analyzed to annotate proteins relevant to disease-resistance response and signal transduction.

CONCLUSIONS

The prediction model based on convolutional neural network was successfully applied to select good candidates of the proteins with functions relevant to the ISR mechanism from the protein sequences which cannot be annotated by database alignment. The waste of sequence data can be avoided, and research time and labor will be saved in further research of protein of creeping bentgrass by molecular biology technology. It also provides reference for other sequence analysis of turfgrass disease-resistance research.

Fungus-originated glucanase and monooxygenase genes in creeping bent grass (Agrostis stolonifera L.)

Recent studies have revealed presence of fungus-originated genes in genomes of cool-season grasses, suggesting occurrence of multiple ancestral gene transfer events between the two distant lineages. The current article describes identification of glucanase-like and monooxygenase-like genes from creeping bent grass, as lateral gene transfer candidates. An in silico analysis suggested presence of the glucanase-like gene in Agrostis, Deyeuxia, and Polypogon genera, but not in other species belonging to the clade 1 of the Poeae tribe. Similarly, the monooxygenase-like gene was confined to Agrostis and Deyeuxia genera. A consistent result was obtained from PCR-based screening. The glucanase-like gene was revealed to be ubiquitously expressed in young seedlings of creeping bent grass. Although expression of the monooxygenase-like gene was suggested in plant tissues, the levels were considerably lower than those of the glucanase-like gene. A phylogenetic analysis revealed close relationships of the two genes between the corresponding genes in fungal endophyte species of the Epichloë genus, suggesting that the genes originated from the Epichloë lineage.

Transcriptional regulation and stress-defensive key genes induced by γ-aminobutyric acid in association with tolerance to water stress in creeping bentgrass

γ-Aminobutyric acid (GABA) acts as an important regulator involved in the mediation of cell signal transduction and stress tolerance in plants. However, the function of GABA in transcriptional regulation is not fully understood in plants under water stress. The creeping bentgrass (Agrostis stolonifera) was pretreated with or without GABA (0.5 mM) for 24 hours before being exposed to 5 days of water stress. Physiological analysis showed that GABA-treated plants maintained significantly higher endogenous GABA content, leaf relative water content, net photosynthetic rate, and lower osmotic potential than untreated plants under water stress. The GABA application also significantly alleviated stress-induced increases in superoxide anion (O2.-) content, hydrogen peroxide (H2O2) content, and electrolyte leakage through enhancing total antioxidant capacity, superoxide dismutase (SOD) activity, and peroxidase (POD) activity in response to water stress. The transcriptomic analysis demonstrated that the GABA-induced changes in differentially expressed genes (DEGs) involved in carbohydrates, amino acids, and secondary metabolism helped to maintain better osmotic adjustment, energy supply, and metabolic homeostasis when creeping bentgrass suffers from water stress. The GABA triggered Ca2+-dependent protein kinase (CDPK) signaling and improved transcript levels of DREB1/2 and WRKY1/24/41 that could be associated with the upregulation of stress-related functional genes such as POD, DHNs, and HSP70 largely contributing to improved tolerance to water stress in relation to the antioxidant, prevention of cell dehydration, and protein protection in leaves.

Real-Time PCR Detection of Clarireedia spp., the Causal Agents of Dollar Spot in Turfgrasses

Dollar spot is one of the most economically important diseases of turfgrasses. Recent taxonomic revisions have placed the dollar spot fungal pathogens in the new genus Clarireedia, with five species described. The main goal of this study was to develop a quantitative real-time PCR (qPCR) molecular detection assay based on the internal transcribed spacer (ITS) of the ribosomal RNA genes to quantify the abundance of Clarireedia spp. from environmental (field) samples. The qPCR assay was able to detect isolates of the four tested Clarireedia spp. but did not cross react with nontarget fungi, including closely related taxa, other turfgrass pathogens, or other fungal species commonly isolated from turfgrass. The assay is capable of detecting as little as 38.0 fg (3.8 × 10^-14 g) of Clarireedia genomic DNA in 3 h. The qPCR assay detected Clarireedia spp. in both symptomatic and asymptomatic creeping bentgrass (Agrostis stolonifera) foliar tissue. Clarireedia spp. were rarely detected in the thatch or soil, indicating that these pathogens are not widely distributed in these areas of the environment. The fact that the pathogen was detected in asymptomatic tissue suggests that creeping bentgrass may be able to tolerate a certain quantity of the pathogens in leaves before disease symptoms appear; however, further research is needed to validate this hypothesis.

iTRAQ-based proteomics reveals key role of γ-aminobutyric acid (GABA) in regulating drought tolerance in perennial creeping bentgrass (Agrostis stolonifera)

γ-Aminobutyric acid (GABA), a non-proteinaceous amino acid, modulates plant growth and stress tolerance. However, the potential role of GABA in regulating key metabolic pathways and stress-defensive proteins against drought in plants has never been explored. Creeping bentgrass (Agrostis stolonifera) plants were pretreated with or without GABA and then subjected to water stress for 8 days in controlled growth chambers (23/19 °C, day/night). Physiological analysis showed that elevated endogenous GABA level via exogenous GABA application significantly mitigated water stress damage to creeping bentgrass, as manifested by increased leaf relative water content, water use efficiency, osmotic adjustment (OA), photochemical efficiency (Fv/Fm), net photosynthetic rate, and reduced oxidative damage. iTRAQ-based proteomics found that enhanced chaperones accumulation, carbohydrates, amino acids, and energy metabolism played important roles in protein protection, OA, energy maintenance, and metabolic balance, which is important adaptive response to drought stress in creeping bentgrass. The GABA further promoted energy production and conversion, antioxidant defense, and DHN3 accumulation that were essential for energy requirement, ROS-scavenging, and the prevention of cell dehydration in leaf during drought stress. In addition, GABA-treated plants maintained significantly higher abundance of dicarboxylate transporter 2.1, ATP-dependent zinc metalloprotease, receptor-like protein kinase HERK1, o-acyltransferase WSD1, omega-6 fatty acid desaturase, and two-component response regulator ORR21 than untreated plants under drought stress. The result provides new evidences that GABA-induced drought tolerance is possibly involved in the improvement of nitrogen recycling, protection of photosystem II, mitigation of drought-depressed cell elongation, wax biosynthesis, fatty acid desaturase, and delaying leaf senescence in creeping bentgrass.

Regulation of Heat Shock Factor Pathways by γ-aminobutyric Acid (GABA) Associated with Thermotolerance of Creeping Bentgrass

Activation and enhancement of heat shock factor (HSF) pathways are important adaptive responses to heat stress in plants. The γ-aminobutyric acid (GABA) plays an important role in regulating heat tolerance, but it is unclear whether GABA-induced thermotolerance is associated with activation of HSF pathways in plants. In this study, the changes of endogenous GABA level affecting physiological responses and genes involved in HSF pathways were investigated in creeping bentgrass during heat stress. The increase in endogenous GABA content induced by exogenous application of GABA effectively alleviated heat damage, as reflected by higher leaf relative water content, cell membrane stability, photosynthesis, and lower oxidative damage. Contrarily, the inhibition of GABA accumulation by the application of GABA biosynthesis inhibitor further aggravated heat damage. Transcriptional analyses showed that exogenous GABA could significantly upregulate transcript levels of genes encoding heat shock factor HSFs (HSFA-6a, HSFA-2c, and HSFB-2b), heat shock proteins (HSP17.8, HSP26.7, HSP70, and HSP90.1-b1), and ascorbate peroxidase 3 (APX3), whereas the inhibition of GABA biosynthesis depressed these genes expression under heat stress. Our results indicate GABA regulates thermotolerance associated with activation and enhancement of HSF pathways in creeping bentgrass.

Recent developments in metabolomics-based research in understanding transgenic grass metabolism

BACKGROUND

Transgenic herbicide-resistant (HR) turfgrass together with its associated, broad spectrum herbicides promise cheap, selective and efficient weed control by excluding infested weeds resulting in turf lawn with high uniformity and aesthetic value. The concept of this "weeding program" initiated from modern biotechnology has been widely implemented in several principal crops including maize, soybean, canola and cotton as early as the 1990s. Transgenic HR turfgrass classified as a genetically modified organism (GMO) has undoubtedly caused public concern with respect to its biosafety and legalities similar to well-established HR crops. Nevertheless, applying metabolomics-based approaches which focuses on the identification of the global metabolic state of a biological system in response to either internal or external stimuli can also provide a comprehensive characterization of transgenic grass metabolism and its involvement in biosecurity and public perception.

AIM OF REVIEW

This review summaries the recent applications of metabolomics applied to HR crops to predict the molecular and physiological phenotypes of HR turfgrass species, glyphosate-resistant Kentucky bluegrass (Poa pratensis L.) and glufosinate-resistant creeping bentgrass (Agrotis stonifera L.). Additionally, this review also presents background knowledge with respect to the application of metabolomics, transformation of HR crops and its biosafety concerns, turfgrass botanical knowledge and its economic and aesthetic value.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The purpose of this review is to demonstrate the molecular and physiological phenotypes of HR turfgrass based on several lines of evidence primarily derived from metabolomics data applied to HR crops to identify alterations on HR turfgrass metabolism as a result of genetic modification that confers resistant traits.

Transgenic creeping bentgrass overexpressing Osa-miR393a exhibits altered plant development and improved multiple stress tolerance

MicroRNA393 (miR393) has been implicated in plant growth, development and multiple stress responses in annual species such as Arabidopsis and rice. However, the role of miR393 in perennial grasses remains unexplored. Creeping bentgrass (Agrostis stolonifera L.) is an environmentally and economically important C3 cool-season perennial turfgrass. Understanding how miR393 functions in this representative turf species would allow the development of novel strategies in genetically engineering grass species for improved abiotic stress tolerance. We have generated and characterized transgenic creeping bentgrass plants overexpressing rice pri-miR393a (Osa-miR393a). We found that Osa-miR393a transgenics had fewer, but longer tillers, enhanced drought stress tolerance associated with reduced stomata density and denser cuticles, improved salt stress tolerance associated with increased uptake of potassium and enhanced heat stress tolerance associated with induced expression of small heat-shock protein in comparison with wild-type controls. We also identified two targets of miR393, AsAFB2 and AsTIR1, whose expression is repressed in transgenics. Taken together, our results revealed the distinctive roles of miR393/target module in plant development and stress responses between creeping bentgrass and other annual species, suggesting that miR393 would be a promising candidate for generating superior crop cultivars with enhanced multiple stress tolerance, thus contributing to agricultural productivity.

Comparative transcriptomic analysis reveals common molecular factors responsive to heat and drought stress in Agrostis stolonifera

Heat and drought stress are primary abiotic stresses confining growth of cool-season grass species during summer. The objective of this study was to identify common molecular factors and metabolic pathways associated with heat and drought responses in creeping bentgrass (Agrostis stolonifera) by comparative analysis of transcriptomic profiles between plants exposed to heat and drought stress. Plants were exposed to heat stress (35/30 °C day/night temperature) or drought stress by withholding irrigation for 21 d in growth chambers. Transcriptomic profiling by RNA-seq in A. stolonifera (cv. 'Penncross') found 670 commonly up-regulated and 812 commonly down-regulated genes by heat and drought stress. Transcriptional up-regulations of differentially expressed genes (DEGs) due to heat and drought stress include genes that were highly enriched in oxylipin biosynthetic process and proline biosynthetic process. Transcriptional down-regulations of genes under heat and drought stress were highly enriched and involved in thiamine metabolic process and calcium sensing receptor. These commonly-regulated genes by heat and drought stress identified in A. stolonifera suggested that drought and heat responses shared such common molecular factors and pathways, which could be potential candidate genes for genetic modification of improving plant tolerance to the combined heat and drought stress.

Transgenic creeping bentgrass plants expressing a Picea wilsonii dehydrin gene (PicW) demonstrate improved freezing tolerance

Agrostis stolonifera L. 'Penn A-4' is a common creeping bentgrass species that is widely used in urban landscaping and golf courses. To prolong the green stage of this grass, a dehydrin gene PicW isolated from Wilson's spruce (Picea wilsonii) was transformed into plants of 'Penn A-4' cultivar via a straightforward stolon node infection system. A putative transgenic plant was obtained and its tolerance to low-temperature stress was evaluated. When the transgenic line was subjected to a freezing (- 5 °C) treatment, it showed better viability and more robust physiology than wild type, as evidenced by higher soluble sugar and proline contents, and lower relative electrical conductivity and malondialdehyde content. The transgenic line also showed tolerance to a chilling treatment (5 °C), although its performance was not significantly different from that of wild-type plants. Overall, the research here clearly revealed the explicit role of PicW in increasing freezing tolerance of grass at the whole-plant level, and demonstrated that the straightforward stolon node transformation method could be well used to genetically modify turfgrass. The obtained transgenic line might be as genetic resource for breeding program and practiced to grow in cold temperate zones.

Transcript Profiling and Gene Identification Involved in the Ethylene Signal Transduction Pathways of Creeping Bentgrass (Agrostis stolonifera) during ISR Response Induced by Butanediol

Creeping bentgrass (Agrostis stolonifera) is the preferred green lawn grass, with excellent turf characteristics but poor disease resistance. At present, the mechanisms of disease resistance in creeping bentgrass are poorly understood, especially the ethylene signal transduction pathway under the induced systemic resistance (ISR) response. In this study, butanediol (BDO), as a new type of disease-resistance compound, was applied to creeping bentgrass seedlings to induce the ISR response. Then, we measured ethylene production and related enzyme activities. Additionally, transcript profiling and gene identification were performed in association to ethylene signal transduction pathways. The changes of ethylene production and related enzyme 1-aminocyclopropane-1-carboxylic acid oxidase (ACO) and 1-aminocyclopropane-1-carboxylic acid synthases (ACS) activities showed significant difference at 24 h after Rhizoctonia solani inoculation among five treatments of various BDO concentrations. After 100 µmol L^-1 BDO treatment, ethylene production and related enzyme activities reached their peak levels. Additionally, 208,672 unigenes of creeping bentgrass were obtained by de novo assembly. In total, 15,903 annotated unigenes were grouped into 33 canonical pathways in the KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis. Among those, 1803 unigenes were classified as 'signal transduction'. There were 6766 differentially expressed genes (DEGs) among B24 (inoculated-rhizobacteria in MS medium with 100 µmol L^-1 BDO for 24 h), NB24, B72 and NB24 (no rhizobacteria in MS medium with 100 µmol L^-1 BDO for 24 h) libraries, and 4,639 DEGs between B24 and B72 (inoculated-rhizobacteria in MS medium with 100 µmol L^-1 BDO for 72 h) libraries, with 4489 DEGs in all three libraries. As suggested by the RT-PCR assay, the expression levels of ethylene-responsive and defense-related genes were variable among treated samples during the BDO-induced ISR responses. The expression levels of EIN, ERF, NPR1, PR3 and PR4 genes increased and reached their peaks in the first 24 h after R. solani infection in the BDO-induced ISR reaction compared with NB24 treatments. This results is consistent with the changes of important ethylene biosynthetic enzymes and ethylene concentrations during the BDO-induced ISR responses. We further found the intermediate substances for the signaling pathway, and the relationships between the expression levels of BDO-induced ISR disease-resistance genes and those of the response genes for ethylene signal pathway. Our findings present a genetic basis for systemic resistance of creeping bentgrass through transcriptomic analysis and our study provides a theoretical and practical basis for the improvement of turfgrass disease resistance and quality.

Transcriptional Responses of Creeping Bentgrass to 2,3-Butanediol, a Bacterial Volatile Compound (BVC) Analogue

Bacterial volatile compounds (BVCs) have been reported to enhance plant growth and elicit plant defenses against fungal infection and insect damage. The objective of this study was to determine transcriptomic changes in response to synthetic BVC that could be associated with plant resistance to Rhizoctonia solani in creeping bentgrass. The 2,3-butanediol (BD) (250 µM) was sprayed on creeping bentgrass leaves grown in jam jars. The result showed that synthetic BD induced plant defense against R. solani for creeping bentgrass. Transcriptomic analysis demonstrated that more genes were repressed by BD while less showed up-regulation. BD suppressed the expression of some regular stress-related genes in creeping bentgrass, such as pheromone activity, calcium channel activity, photosystem II oxygen evolving complex, and hydrolase activity, while up-regulated defense related transcription factors (TFs), such as basic helix-loop-helix (bHLH) TFs, cysteine2-cysteine2-contans-like (C2C2-CO) and no apical meristem TFs (NAC). Other genes related to disease resistance, such as jasmonic acid (JA) signaling, leucine rich repeats (LRR)-transmembrane protein kinase, pathogen-related (PR) gene 5 receptor kinase and nucleotide binding site-leucine rich repeats (NBS-LRR) domain containing plant resistance gene (R-gene) were also significantly up-regulated. These results suggest that BD may induce changes to the plant transcriptome in induced systemic resistance (ISR) pathways.

Expression in grasses of multiple transgenes for degradation of munitions compounds on live-fire training ranges

The deposition of toxic munitions compounds, such as hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX), on soils around targets in live-fire training ranges is an important source of groundwater contamination. Plants take up RDX but do not significantly degrade it. Reported here is the transformation of two perennial grass species, switchgrass (Panicum virgatum) and creeping bentgrass (Agrostis stolonifera), with the genes for degradation of RDX. These species possess a number of agronomic traits making them well equipped for the uptake and removal of RDX from root zone leachates. Transformation vectors were constructed with xplA and xplB, which confer the ability to degrade RDX, and nfsI, which encodes a nitroreductase for the detoxification of the co-contaminating explosive 2, 4, 6-trinitrotoluene (TNT). The vectors were transformed into the grass species using Agrobacterium tumefaciens infection. All transformed grass lines showing high transgene expression levels removed significantly more RDX from hydroponic solutions and retained significantly less RDX in their leaf tissues than wild-type plants. Soil columns planted with the best-performing switchgrass line were able to prevent leaching of RDX through a 0.5-m root zone. These plants represent a promising plant biotechnology to sustainably remove RDX from training range soil, thus preventing contamination of groundwater.

Transcriptome analysis of creeping bentgrass exposed to drought stress and polyamine treatment

Creeping bentgrass is an important cool-season turfgrass species sensitive to drought. Treatment with polyamines (PAs) has been shown to improve drought tolerance; however, the mechanism is not yet fully understood. Therefore, this study aimed to evaluate transcriptome changes of creeping bentgrass in response to drought and exogenous spermidine (Spd) application using RNA sequencing (RNA-Seq). The high-quality sequences were assembled and 18,682 out of 49,190 (38%) were detected as coding sequences. A total of 22% and 19% of genes were found to be either up- or down-regulated due to drought while 20% and 34% genes were either up- or down- regulated in response to Spd application under drought conditions, respectively. Gene ontology (GO) and enrichment analysis were used to interpret the biological processes of transcripts and relative transcript abundance. Enriched or differentially expressed transcripts due to drought stress and/or Spd application were primarily associated with energy metabolism, transport, antioxidants, photosynthesis, signaling, stress defense, and cellular response to water deprivation. This research is the first to provide transcriptome data for creeping bentgrass under an abiotic stress using RNA-Seq analysis. Differentially expressed transcripts identified here could be further investigated for use as molecular markers or for functional analysis in responses to drought and Spd.

Ectopic expression of a cyanobacterial flavodoxin in creeping bentgrass impacts plant development and confers broad abiotic stress tolerance

Flavodoxin (Fld) plays a pivotal role in photosynthetic microorganisms as an alternative electron carrier flavoprotein under adverse environmental conditions. Cyanobacterial Fld has been demonstrated to be able to substitute ferredoxin of higher plants in most electron transfer processes under stressful conditions. We have explored the potential of Fld for use in improving plant stress response in creeping bentgrass (Agrostis stolonifera L.). Overexpression of Fld altered plant growth and development. Most significantly, transgenic plants exhibited drastically enhanced performance under oxidative, drought and heat stress as well as nitrogen (N) starvation, which was associated with higher water retention and cell membrane integrity than wild-type controls, modified expression of heat-shock protein genes, production of more reduced thioredoxin, elevated N accumulation and total chlorophyll content as well as up-regulated expression of nitrite reductase and N transporter genes. Further analysis revealed that the expression of other stress-related genes was also impacted in Fld-expressing transgenics. Our data establish a key role of Fld in modulating plant growth and development and plant response to multiple sources of adverse environmental conditions in crop species. This demonstrates the feasibility of manipulating Fld in crop species for genetic engineering of plant stress tolerance.

Pollen-mediated gene flow from transgenic perennial creeping bentgrass and hybridization at the landscape level

The planting of 162 ha of transgenic glyphosate-resistant creeping bentgrass (Agrostis stolonifera) near Madras, OR, USA, allowed a unique opportunity to study gene flow over time from a perennial outcrossing species at the landscape level. While conducting a four year in situ survey, we collected panicles and leaf tissue samples from creeping bentgrass and its sexually compatible species. Seeds from the panicles were planted, and seedlings were tested in the greenhouse for expression of the transgene. Gene flow via pollen was found in all four years, at frequencies of 0.004 to 2.805%. Chloroplast markers, in combination with internal transcribed spacer nuclear sequence analysis, were used to aid in identification of transgenic interspecific and intergeneric hybrid seedlings found during the testing and of established plants that could not be positively identified in the field. Interspecific transgenic hybrids produced on redtop (Agrostis gigantea) plants in situ were identified three of the four years and one intergeneric transgenic creeping bentgrass x rabbitfoot grass (Polypogon monspeliensis) hybrid was identified in 2005. In addition, we confirmed a non-transgenic creeping bentgrass x redtop hybrid in situ, demonstrating that interspecific hybrids have established in the environment outside production fields. Results of this study should be considered for deregulation of transgenic events, studies of population dynamics, and prediction of gene flow in the environment.

Candidate genes and molecular markers associated with heat tolerance in colonial Bentgrass

Elevated temperature is a major abiotic stress limiting the growth of cool-season grasses during the summer months. The objectives of this study were to determine the genetic variation in the expression patterns of selected genes involved in several major metabolic pathways regulating heat tolerance for two genotypes contrasting in heat tolerance to confirm their status as potential candidate genes, and to identify PCR-based markers associated with candidate genes related to heat tolerance in a colonial (Agrostis capillaris L.) x creeping bentgrass (Agrostis stolonifera L.) hybrid backcross population. Plants were subjected to heat stress in controlled-environmental growth chambers for phenotypic evaluation and determination of genetic variation in candidate gene expression. Molecular markers were developed for genes involved in protein degradation (cysteine protease), antioxidant defense (catalase and glutathione-S-transferase), energy metabolism (glyceraldehyde-3-phosphate dehydrogenase), cell expansion (expansin), and stress protection (heat shock proteins HSP26, HSP70, and HSP101). Kruskal-Wallis analysis, a commonly used non-parametric test used to compare population individuals with or without the gene marker, found the physiological traits of chlorophyll content, electrolyte leakage, normalized difference vegetative index, and turf quality were associated with all candidate gene markers with the exception of HSP101. Differential gene expression was frequently found for the tested candidate genes. The development of candidate gene markers for important heat tolerance genes may allow for the development of new cultivars with increased abiotic stress tolerance using marker-assisted selection.

Differentially Expressed Genes Associated with Improved Drought Tolerance in Creeping Bentgrass Overexpressing a Gene for Cytokinin Biosynthesis

Transformation with an isopentenyl transferase (ipt) gene controlling cytokinin (CK) synthesis has been shown to enhance plant drought tolerance. The objective of this study was to identify differentially-expressed genes (DEGs) in creeping bentgrass (Agrostis stolonifera) overexpressing ipt compared to non-transgenic plants. The ipt transgene was controlled by a senescence-activated promoter (SAG12). Both a null transformed line (NT) and SAG12-ipt plants were exposed to drought stress in an environmentally-controlled growth chamber until the soil water content declined to approximately 5% and leaf relative water content declined to 47%, which were both significantly below the well-watered controls. RNA was extracted from leaf samples of both well-watered and drought-stressed plants. Eight sets of subtractive hybridizations were performed for detection of up-regulated and down-regulated genes due to the presence of the transgene and due to drought stress in both NT and transgenic plants. Sequencing analysis revealed the identity of 252 DEGs due to either the transgene and drought stress. Sequencing analysis of 170 DEGs identified genes encoding for proteins that were related to energy production, metabolism, stress defense, signaling, protein synthesis and transport, and membrane transport could play major roles in the improved drought tolerance by overexpressing ipt in creeping bentgrass.

Chlorophyll loss associated with heat-induced senescence in bentgrass

Heat stress-induced leaf senescence is characterized by the loss of chlorophyll from leaf tissues. The objectives of this study were to examine genetic variations in the level of heat-induced leaf senescence in hybrids of colonial (Agrostis capillaris)×creeping bentgrass (Agrostis stolonifera) contrasting in heat tolerance, and determine whether loss of leaf chlorophyll during heat-induced leaf senescence was due to suppressed chlorophyll synthesis and/or accelerated chlorophyll degradation in the cool-season perennial grass species. Plants of two hybrid backcross genotypes ('ColxCB169' and 'ColxCB190') were exposed to heat stress (38/33°C, day/night) for 28 d in growth chambers. The analysis of turf quality, membrane stability, photochemical efficiency, and chlorophyll content demonstrated significant variations in the level of leaf senescence induced by heat stress between the two genotypes, with ColXCB169 exhibiting a lesser degree of decline in chlorophyll content, photochemical efficiency and membrane stability than ColXCB190. The assays of enzymatic activity or gene expression of several major chlorophyll-synthesizing (porphobilinogen deaminase, Mg-chelatase, protochlorophyllide-reductase) and chlorophyll-degrading enzymes (chlorophyllase, pheophytinase, and chlorophyll-degrading peroxidase) indicated heat-induced decline in leaf chlorophyll content was mainly due to accelerated chlorophyll degradation, as manifested by increased gene expression levels of chlorophyllase and pheophytinase, and the activity of pheophytinase (PPH), while chlorophyll-synthesizing genes and enzymatic activities were not differentially altered by heat stress in the two genotypes. The analysis of heat-induced leaf senescence of pph mutants of Arabidopsis further confirmed that PPH could be one enzymes that plays key roles in regulating heat-accelerated chlorophyll degradation. Further research on enzymes responsible in part for the loss of chlorophyll during heat-induced senescence could aid in the development of genotypes with stay-green traits either through marker assisted selection or transgenic approaches.

AsHSP17, a creeping bentgrass small heat shock protein modulates plant photosynthesis and ABA-dependent and independent signalling to attenuate plant response to abiotic stress

Heat shock proteins (HSPs) are molecular chaperones that accumulate in response to heat and other abiotic stressors. Small HSPs (sHSPs) belong to the most ubiquitous HSP subgroup with molecular weights ranging from 12 to 42 kDa. We have cloned a new sHSP gene, AsHSP17 from creeping bentgrass (Agrostis stolonifera) and studied its role in plant response to environmental stress. AsHSP17 encodes a protein of 17 kDa. Its expression was strongly induced by heat in both leaf and root tissues, and by salt and abscisic acid (ABA) in roots. Transgenic Arabidopsis plants constitutively expressing AsHSP17 exhibited enhanced sensitivity to heat and salt stress accompanied by reduced leaf chlorophyll content and decreased photosynthesis under both normal and stressed conditions compared to wild type. Overexpression of AsHSP17 also led to hypersensitivity to exogenous ABA and salinity during germination and post-germinative growth. Gene expression analysis indicated that AsHSP17 modulates expression of photosynthesis-related genes and regulates ABA biosynthesis, metabolism and ABA signalling as well as ABA-independent stress signalling. Our results suggest that AsHSP17 may function as a protein chaperone to negatively regulate plant responses to adverse environmental stresses through modulating photosynthesis and ABA-dependent and independent signalling pathways.

Enhancing cytokinin synthesis by overexpressing ipt alleviated drought inhibition of root growth through activating ROS-scavenging systems in Agrostis stolonifera

Drought stress limits root growth and inhibits cytokinin (CK) production. Increases in CK production through overexpression of isopentenyltransferase (ipt) alleviate drought damages to promote root growth. The objective of this study was to investigate whether CK-regulated root growth was involved in the alteration of reactive oxygen species (ROS) production and ROS scavenging capacity under drought stress. Wild-type (WT) creeping bentgrass (Agrostis stolonifera L. 'Penncross') and a transgenic line (S41) overexpressing ipt ligated to a senescence-activated promoter (SAG12) were exposed to drought stress for 21 d in growth chambers. SAG12-ipt transgenic S41 developed a more extensive root system under drought stress compared to the WT. Root physiological analysis (electrolyte leakage and lipid peroxidation) showed that S41 roots exhibited less cellular damage compared to the WT under drought stress. Roots of SAG12-ipt transgenic S41 had significantly higher endogenous CK content than the WT roots under drought stress. ROS (hydrogen peroxide and superoxide) content was significantly lower and content of total and free ascorbate was significantly higher in S41 roots compared to the WT roots under drought stress. Enzymatic assays and transcript abundance analysis showed that superoxide dismutase, catalase, peroxidase, and dehydroascorbate reductase were significantly higher in S41 roots compared to the WT roots under drought stress. S41 roots also maintained significantly higher alternative respiration rates compared to the WT under drought stress. The improved root growth of transgenic creeping bentgrass may be facilitated by CK-enhanced ROS scavenging through antioxidant accumulation and activation of antioxidant enzymes, as well as higher alternative respiration rates when soil water is limited.

Selection of reference genes for quantitative real-time PCR normalization in creeping bentgrass involved in four abiotic stresses

This study identified stable reference genes for normalization of gene expression data in qRT-PCR analysis of leaf and root tissues in creeping bentgrass under four abiotic stresses. Examination of gene expression using quantitative real-time PCR (qRT-PCR) in plant responses to abiotic stresses can provide valuable information for stress-tolerance improvement. Selecting stable reference genes for qRT-PCR analysis is critically important. The objective of this study was to determine the stability of expression for eight candidate reference genes (ACT, EF1a, TUB, UPL7, GAPDH, PP2A, PEPKR1, and CACS) in two tissues (roots and leaves) of a perennial grass species under four abiotic stresses (salt, drought, cold, and heat) using four programs (GeNorm, NormFinder, BestKeeper, and RefFinder). The results showed that (1) the combinations of CACS and UPL7 or PP2A and ACT were stably expressed in salt-treated roots or leaves; (2) the combinations of GAPDH and CACS or PP2A and PEPKR1 were stable in roots and leaves under drought stress; (3) CACS and PP2A exhibited stable expression in cold-treated roots and the combination of EF1a and UPL7 was also stable in cold-treated leaves; and (4) CACS and PP2A were the two most stable reference genes in heat-stressed roots and UPL7 combined with GAPDH and PP2A was stably expressed in heat-stressed leaves. The qRT-PCR analysis of a target gene, AsSAP expression patterns in response to salinity and drought stress, confirmed the reliability of those selected and stable reference genes. Identification of stable reference genes in creeping bentgrass will improve assay accuracy for selecting stress-tolerance genes and identifying molecular mechanisms conferring stress tolerance in this species.

Root Antioxidant Mechanisms in Relation to Root Thermotolerance in Perennial Grass Species Contrasting in Heat Tolerance

Mechanisms of plant root tolerance to high temperatures through antioxidant defense are not well understood. The objective of this study was to investigate whether superior root thermotolerance of heat-tolerant Agrostis scabra relative to its congeneric heat-sensitive Agrostis stolonifera was associated with differential accumulation of reactive oxygen species and antioxidant scavenging systems. A. scabra ‘NTAS’ and A. stolonifera ‘Penncross’ plants were exposed to heat stress (35/30°C, day/night) in growth chambers for 24 d. Superoxide (O₂^-) content increased in both A. stolonifera and A. scabra roots under heat stress but to a far lesser extent in A. scabra than in A. stolonifera. Hydrogen peroxide (H₂O₂) content increased significantly in A. stolonifera roots but not in A. scabra roots responding to heat stress. The content of antioxidant compounds (ascorbate and glutathione) did not differ between A. stolonifera and A. scabra under heat stress. Enzymatic activity of superoxide dismutase was less suppressed in A. scabra than that in A. stolonifera under heat stress, while peroxidase and catalase were more induced in A. scabra than in A. stolonifera. Similarly, their encoded transcript levels were either less suppressed, or more induced in A. scabra roots than those in A. stolonifera during heat stress. Roots of A. scabra exhibited greater alternative respiration rate and lower cytochrome respiration rate under heat stress, which was associated with suppression of O₂^- and H₂O₂ production as shown by respiration inhibitors. Superior root thermotolerance of A. scabra was related to decreases in H₂O₂ and O₂^- accumulation facilitated by active enzymatic antioxidant defense systems and the maintenance of alternative respiration, alleviating cellular damages by heat-induced oxidative stress.

Constitutive Expression of Rice MicroRNA528 Alters Plant Development and Enhances Tolerance to Salinity Stress and Nitrogen Starvation in Creeping Bentgrass

MicroRNA528 (miR528) is a conserved monocot-specific small RNA that has the potential of mediating multiple stress responses. So far, however, experimental functional studies of miR528 are lacking. Here, we report that overexpression of a rice (Oryza sativa) miR528 (Osa-miR528) in transgenic creeping bentgrass (Agrostis stolonifera) alters plant development and improves plant salt stress and nitrogen (N) deficiency tolerance. Morphologically, miR528-overexpressing transgenic plants display shortened internodes, increased tiller number, and upright growth. Improved salt stress resistance is associated with increased water retention, cell membrane integrity, chlorophyll content, capacity for maintaining potassium homeostasis, CATALASE activity, and reduced ASCORBIC ACID OXIDASE (AAO) activity; while enhanced tolerance to N deficiency is associated with increased biomass, total N accumulation and chlorophyll synthesis, nitrite reductase activity, and reduced AAO activity. In addition, AsAAO and COPPER ION BINDING PROTEIN1 are identified as two putative targets of miR528 in creeping bentgrass. Both of them respond to salinity and N starvation and are significantly down-regulated in miR528-overexpressing transgenics. Our data establish a key role that miR528 plays in modulating plant growth and development and in the plant response to salinity and N deficiency and indicate the potential of manipulating miR528 in improving plant abiotic stress resistance.

Characterization of a small constitutive promoter from Arabidopsis translationally controlled tumor protein (AtTCTP) gene for plant transformation

A plant-derived 0.3 kb constitutive promoter was obtained from AtTCTP expression analysis, and successfully applied to the expression of a selectable marker gene for production of transgenic creeping bentgrass plants. The isolation and use of an efficient promoter is essential to develop a vector system for efficient genetic transformation of plants, and constitutive promoters are particularly useful for the expression of selectable marker genes. In this study, we characterized a small size of the constitutive promoter from the expression analysis of Arabidopsis thaliana translationally controlled tumor protein (AtTCTP) gene. Histochemical and fluorometric GUS analyses revealed that a 303 bp upstream region from the start codon of the AtTCTP gene showed strong GUS expression throughout all plant tissues, which is approximately 55 % GUS activity compared with the cauliflower mosaic virus 35S promoter (35Spro). To examine the possible application of this promoter for the development of genetically engineered crops, we introduced pCAMBIA3301 vector harboring the 0.3 kb promoter of AtTCTP (0.3kbpro) that was fused to the herbicide resistance BAR gene (0.3kb pro ::BAR) into creeping bentgrass. Our transformation results demonstrate that transgenic creeping bentgrass plants with herbicide resistance were successfully produced using 0.3kb pro ::BAR as a selectable marker. Northern blot analysis revealed that the transgenic plants with 0.3kb pro ::BAR showed reduced but comparable expression levels of BAR to those with 35S pro ::BAR. Moreover, the transcription activity of the 0.3 kb promoter could be increased by the fusion of an enhancer sequence. These results indicate that the 0.3 kb AtTCTP promoter can be used as a plant-derived constitutive promoter for the expression of selectable marker genes, which facilitates its use as an alternative to the 35S promoter for developing genetically engineered crops.

Overexpression of the synthetic chimeric native-T-phylloplanin-GFP genes optimized for monocot and dicot plants renders enhanced resistance to blue mold disease in tobacco (N. tabacum L.)

To enhance the natural plant resistance and to evaluate the antimicrobial properties of phylloplanin against blue mold, we have expressed a synthetic chimeric native-phylloplanin-GFP protein fusion in transgenic Nicotiana tabacum cv. KY14, a cultivar that is highly susceptible to infection by Peronospora tabacina. The coding sequence of the tobacco phylloplanin gene along with its native signal peptide was fused with GFP at the carboxy terminus. The synthetic chimeric gene (native-phylloplanin-GFP) was placed between the modified Mirabilis mosaic virus full-length transcript promoter with duplicated enhancer domains and the terminator sequence from the rbcSE9 gene. The chimeric gene, expressed in transgenic tobacco, was stably inherited in successive plant generations as shown by molecular characterization, GFP quantification, and confocal fluorescent microscopy. Transgenic plants were morphologically similar to wild-type plants and showed no deleterious effects due to transgene expression. Blue mold-sensitivity assays of tobacco lines were performed by applying P. tabacina sporangia to the upper leaf surface. Transgenic lines expressing the fused synthetic native-phyllopanin-GFP gene in the leaf apoplast showed resistance to infection. Our results demonstrate that in vivo expression of a synthetic fused native-phylloplanin-GFP gene in plants can potentially achieve natural protection against microbial plant pathogens, including P. tabacina in tobacco.

Comparative genome analysis between Agrostis stolonifera and members of the Pooideae subfamily, including Brachypodium distachyon

Creeping bentgrass (Agrostis stolonifera, allotetraploid 2n = 4x = 28) is one of the major cool-season turfgrasses. It is widely used on golf courses due to its tolerance to low mowing and aggressive growth habit. In this study, we investigated genome relationships of creeping bentgrass relative to the Triticeae (a consensus map of Triticum aestivum, T. tauschii, Hordeum vulgare, and H. spontaneum), oat, rice, and ryegrass maps using a common set of 229 EST-RFLP markers. The genome comparisons based on the RFLP markers revealed large-scale chromosomal rearrangements on different numbers of linkage groups (LGs) of creeping bentgrass relative to the Triticeae (3 LGs), oat (4 LGs), and rice (8 LGs). However, we detected no chromosomal rearrangement between creeping bentgrass and ryegrass, suggesting that these recently domesticated species might be closely related, despite their memberships to different Pooideae tribes. In addition, the genome of creeping bentgrass was compared with the complete genome sequence of Brachypodium distachyon in Pooideae subfamily using both sequences of the above-mentioned mapped EST-RFLP markers and sequences of 8,470 publicly available A. stolonifera ESTs (AgEST). We discovered large-scale chromosomal rearrangements on six LGs of creeping bentgrass relative to B. distachyon. Also, a total of 24 syntenic blocks based on 678 orthologus loci were identified between these two grass species. The EST orthologs can be utilized in further comparative mapping of Pooideae species. These results will be useful for genetic improvement of Agrostis species and will provide a better understanding of evolution within Pooideae species.

Heterologous expression of OsSIZ1, a rice SUMO E3 ligase, enhances broad abiotic stress tolerance in transgenic creeping bentgrass

Sumoylation is a posttranslational regulatory process in higher eukaryotes modifying substrate proteins through conjugation of small ubiquitin-related modifiers (SUMOs). Sumoylation modulates protein stability, subcellular localization and activity; thus, it regulates most cellular functions including response to environmental stress in plants. To study the feasibility of manipulating SUMO E3 ligase, one of the important components in the sumoylation pathway in transgenic (TG) crop plants for improving overall plant performance under adverse environmental conditions, we have analysed TG creeping bentgrass (Agrostis stolonifera L.) plants constitutively expressing OsSIZ1, a rice SUMO E3 ligase. Overexpression of OsSIZ1 led to increased photosynthesis and overall plant growth. When subjected to water deficiency and heat stress, OsSIZ1 plants exhibited drastically enhanced performance associated with more robust root growth, higher water retention and cell membrane integrity than wild-type (WT) controls. OsSIZ1 plants also displayed significantly better growth than WT controls under phosphate-starvation conditions, which was associated with a higher uptake of phosphate (Pi) and other minerals, such as potassium and zinc. Further analysis revealed that overexpression of OsSIZ1 enhanced stress-induced SUMO conjugation to substrate in TG plants, which was associated with modified expression of stress-related genes. This strongly supports a role sumoylation plays in regulating multiple molecular pathways involved in plant stress response, establishing a direct link between sumoylation and plant response to environmental adversities. Our results demonstrate the great potential of genetic manipulation of sumoylation process in TG crop species for improved resistance to broad abiotic stresses.

Constitutive expression of a miR319 gene alters plant development and enhances salt and drought tolerance in transgenic creeping bentgrass

MicroRNA319 (miR319) is one of the first characterized and conserved microRNA families in plants and has been demonstrated to target TCP (for TEOSINTE BRANCHED/CYCLOIDEA/PROLIFERATING CELL FACTORS [PCF]) genes encoding plant-specific transcription factors. MiR319 expression is regulated by environmental stimuli, suggesting its involvement in plant stress response, although experimental evidence is lacking and the underlying mechanism remains elusive. This study investigates the role that miR319 plays in the plant response to abiotic stress using transgenic creeping bentgrass (Agrostis stolonifera) overexpressing a rice (Oryza sativa) miR319 gene, Osa-miR319a. We found that transgenic plants overexpressing Osa-miR319a displayed morphological changes and exhibited enhanced drought and salt tolerance associated with increased leaf wax content and water retention but reduced sodium uptake. Gene expression analysis indicated that at least four putative miR319 target genes, AsPCF5, AsPCF6, AsPCF8, and AsTCP14, and a homolog of the rice NAC domain gene AsNAC60 were down-regulated in transgenic plants. Our results demonstrate that miR319 controls plant responses to drought and salinity stress. The enhanced abiotic stress tolerance in transgenic plants is related to significant down-regulation of miR319 target genes, implying their potential for use in the development of novel molecular strategies to genetically engineer crop species for enhanced resistance to environmental stress.

Overexpression of phytochrome A and its hyperactive mutant improves shade tolerance and turf quality in creeping bentgrass and zoysiagrass

Phytochrome A (phyA) in higher plants is known to function as a far-red/shade light-sensing photoreceptor in suppressing shade avoidance responses (SARs) to shade stress. In this paper, the Avena PHYA gene was introduced into creeping bentgrass (Agrostis stolonifera L.) and zoysiagrass (Zoysia japonica Steud.) to improve turf quality by suppressing the SARs. In addition to wild-type PHYA, a hyperactive mutant gene (S599A-PHYA), in which a phosphorylation site involved in light-signal attenuation was removed, was also transformed into the turfgrasses. Phenotypic traits of the transgenic plants were compared to assess the suppression of SARs under a simulated shade condition and outdoor field conditions after three growth seasons. Under the shade condition, the S599A-PhyA transgenic creeping bentgrass plants showed shade avoidance-suppressing phenotypes with a 45 % shorter leaf lengths, 24 % shorter internode lengths, and twofold increases in chlorophyll concentrations when compared with control plants. Transgenic zoysiagrass plants overexpressing S599A-PHYA also showed shade-tolerant phenotypes under the shade condition with reductions in leaf length (15 %), internode length (30 %), leaf length/width ratio (19 %) and leaf area (22 %), as well as increases in chlorophyll contents (19 %) and runner lengths (30 %) compared to control plants. The phenotypes of transgenic zoysiagrass were also investigated in dense field habitats, and the transgenic turfgrass exhibited shade-tolerant phenotypes similar to those observed under laboratory shade conditions. Therefore, the present study suggests that the hyperactive phyA is effective for the development of shade-tolerant plants, and that the shade tolerance nature is sustained under field conditions.

Crossing the divide: gene flow produces intergeneric hybrid in feral transgenic creeping bentgrass population

Gene flow is the most frequently expressed public concern related to the deregulation of transgenic events (Snow 2002; Ellstrand 2003). However, assessing the potential for transgene escape is complex because it depends on the opportunities for unintended gene flow, and establishment and persistence of the transgene in the environment (Warwick et al. 2008). Creeping bentgrass (Agrostis stolonifera L.), a turfgrass species widely used on golf courses, has been genetically engineered to be resistant to glyphosate, a nonselective herbicide. Outcrossing species, such as creeping bentgrass (CB), which have several compatible species, have greater chances for gene escape and spontaneous hybridization (i.e. natural, unassisted sexual reproduction between taxa in the field), which challenges transgene containment. Several authors have emphasized the need for evidence of spontaneous hybridization to infer the potential for gene flow (Armstrong et al. 2005). Here we report that a transgenic intergeneric hybrid has been produced as result of spontaneous hybridization of a feral-regulated transgenic pollen receptor (CB) and a nontransgenic pollen donor (rabbitfoot grass, RF, Polypogon monspeliensis (L.) Desf.). We identified an off-type transgenic seedling and confirmed it to be CB × RF intergeneric hybrid. This first report of a transgenic intergeneric hybrid produced in situ with a regulated transgenic event demonstrates the importance of considering all possible avenues for transgene spread at the landscape level before planting a regulated transgenic crop in the field. Spontaneous hybridization adds a level of complexity to transgene monitoring, containment, mitigation and remediation programmes.

Overexpression of an Arabidopsis β-glucosidase gene enhances drought resistance with dwarf phenotype in creeping bentgrass

An Arabidopsis β-glucosidase, AtBG1 is known to hydrolyze glucose-conjugated, biologically inactive abscisic acid (ABA) to produce active ABA, which increases the level of ABA in plants. Since an increase of ABA in plants confers tolerance against abiotic stress such as drought, we introduced the pCAMBIA3301 vector harboring the AtBG1 gene into creeping bentgrass through Agrobacterium-mediated transformation. After transformation, putative transgenic plants were selected using the BASTA resistance assay at a concentration of 0.8%. Genomic integration of the AtBG1 gene was confirmed by genomic PCR and Southern blot analysis, and gene expression was validated by Northern blot and Western blot analyses. Interestingly, the transgenic bentgrass plants overexpressing AtBG1 had a dwarf phenotype with reduced growth rates when compared to wild-type creeping bentgrass. In addition, the transgenic plants accumulated higher ABA levels and displayed enhanced drought tolerance. These results suggest that the expression of AtBG1 in plants induces the accumulation of higher ABA levels, which results in the formation of dwarf creeping bentgrass and enhances the survival in water-limiting environments.

KEY MESSAGE

We used an Arabidopsis β-glucosidase AtBG1 to engineer a crop with elevated active ABA levels, and developed transgenic creeping bentgrass with enhanced drought tolerance and dwarf phenotype.

Cloning of a Zoysia ZjLsL and its overexpression to induce axillary meristem initiation and tiller formation in Arabidopsis and bentgrass

Zoysia grass and creeping bentgrass are important turf grasses used in parks, gardens and playing fields. Development of grasses with increased tiller formation will enhance their commercial cultivation. To investigate the regulatory mechanism of tiller formation, we cloned the Zoysia japonica Lateral suppressor-like (ZjLsL) gene. The Lateral suppressor (Ls) gene encodes a transcriptional regulator belonging to the plant-specific GRAS protein family of putative transcription factors, and regulates axillary meristem initiation. A full-length DNA of the ZjLsL gene was isolated by 5'/3' DNA walking. Phylogenetic analysis showed that ZjLsL is closely related to Ls genes. Southern blot analysis revealed that zoysia grass has two copies of the ZjLsL gene. ZjLsL expression was detected in all organs of zoysia grass but was most highly expressed in culms. Overexpression of ZjLsL in creeping bentgrass and Arabidopsis plants promoted axillary bud formation. These results suggest that ZjLsL plays an important role in axillary meristem initiation and tiller formation.

Manipulating expression of tonoplast transporters

Plant vacuoles have multifaceted roles including turgor maintenance, cytosolic pH and ionic homeostasis, plant protection against environmental stress, detoxification, pigmentation, and cellular signaling. These roles are achieved through the coordinated activities of many proteins in the tonoplast (vacuolar membrane), of which the proton pumps and ion transporters have been modified for improved abiotic stress tolerance in transgenic plants. Here we describe a method to manipulate vacuolar H(+)-pyrophosphatase in turfgrass and evaluate the impact of the modified tonoplast on the phenotype, biochemistry, and physiology of the transgenics. Creeping bentgrass (Agrostis stolonifera L.) plants overexpressing an Arabidopsis vacuolar H(+)-pyrophosphatase AVP1 exhibited improved growth and enhanced salt tolerance, likely associated with increased photosynthesis, relative water content, proline production, and Na(+) uptake. These transgenic plants also had decreased solute leakage in the leaf tissues and increased concentrations of Na(+), K(+), Cl(-), and total phosphorus in the root tissues. Similar strategies can be employed to manipulate other tonoplast transporters and in other plant species to produce transgenic plants with improved performance under various abiotic stresses.

Protein accumulation in leaves and roots associated with improved drought tolerance in creeping bentgrass expressing an ipt gene for cytokinin synthesis

Cytokinins (CKs) may be involved in the regulation of plant adaptation to drought stress. The objectives of the study were to identify proteomic changes in leaves and roots in relation to improved drought tolerance in transgenic creeping bentgrass (Agrostis stolonifera) containing a senescence-activated promoter (SAG12) and the isopentyl transferase (ipt) transgene that increases endogenous CK content. Leaves of SAG12-ipt bentgrass exhibited less severe senescence under water stress, as demonstrated by maintaining lower electrolyte leakage and lipid peroxidation, and higher photochemical efficiency (F(v)/F(m)), compared with the null transformant (NT) plants. SAG12-ipt plants had higher root/shoot ratios and lower lipid peroxidation in leaves under water stress than the NT plants. The suppression of drought-induced leaf senescence and root dieback in the transgenic plants was associated with the maintenance of greater antioxidant enzyme activities (superoxide dismutase, peroxidase, and catalase). The SAG12-ipt and NT plants exhibited differential protein expression patterns under well-watered and drought conditions in both leaves and roots. Under equivalent leaf water deficit (47% relative water content), SAG12-ipt plants maintained higher abundance of proteins involved in (i) energy production within both photosynthesis and respiration [ribulose 1,5-bisphosphate carboxylase (RuBisCO) and glyceraldehyde phosphate dehydrogenase (GAPDH)]; (ii) amino acid synthesis (methionine and glutamine); (iii) protein synthesis and destination [chloroplastic elongation factor (EF-Tu) and protein disulphide isomerases (PDIs)]; and (iv) antioxidant defence system (catalase and peroxidase) than the NT plants. These results suggest that increased endogenous CKs under drought stress may directly or indirectly regulate protein abundance and enzymatic activities involved in the above-mentioned metabolic processes, thereby enhancing plant drought tolerance.

Expression of a novel antimicrobial peptide Penaeidin4-1 in creeping bentgrass (Agrostis stolonifera L.) enhances plant fungal disease resistance

Background

Turfgrass species are agriculturally and economically important perennial crops. Turfgrass species are highly susceptible to a wide range of fungal pathogens. Dollar spot and brown patch, two important diseases caused by fungal pathogens Sclerotinia homoecarpa and Rhizoctonia solani, respectively, are among the most severe turfgrass diseases. Currently, turf fungal disease control mainly relies on fungicide treatments, which raises many concerns for human health and the environment. Antimicrobial peptides found in various organisms play an important role in innate immune response.

Methodology/Principal Findings

The antimicrobial peptide - Penaeidin4-1 (Pen4-1) from the shrimp, Litopenaeus setiferus has been reported to possess in vitro antifungal and antibacterial activities against various economically important fungal and bacterial pathogens. In this study, we have studied the feasibility of using this novel peptide for engineering enhanced disease resistance into creeping bentgrass plants (Agrostis stolonifera L., cv. Penn A-4). Two DNA constructs were prepared containing either the coding sequence of a single peptide, Pen4-1 or the DNA sequence coding for the transit signal peptide of the secreted tobacco AP24 protein translationally fused to the Pen4-1 coding sequence. A maize ubiquitin promoter was used in both constructs to drive gene expression. Transgenic turfgrass plants containing different DNA constructs were generated by Agrobacterium-mediated transformation and analyzed for transgene insertion and expression. In replicated in vitro and in vivo experiments under controlled environments, transgenic plants exhibited significantly enhanced resistance to dollar spot and brown patch, the two major fungal diseases in turfgrass. The targeting of Pen4-1 to endoplasmic reticulum by the transit peptide of AP24 protein did not significantly impact disease resistance in transgenic plants.

Conclusion/Significance

Our results demonstrate the effectiveness of Pen4-1 in a perennial species against fungal pathogens and suggest a potential strategy for engineering broad-spectrum fungal disease resistance in crop species.

Development of antibiotic marker-free creeping bentgrass resistance against herbicides

Herbicide-resistant creeping bentgrass plants (Agrostis stolonifera L.) without antibiotic-resistant markers were produced by Agrobacterium-mediated transformation. Embryogenic callus tissues were infected with Agrobacterium tumefaciens EHA105, harboring the bar and the CP4-EPSPS genes for bialaphos and glyphosate resistance. Phosphinothricin-resistant calli and plants were selected. Soil-grown plants were obtained at 14-16 weeks after transformation. Genetic transformation of the selected, regenerated plants was validated by PCR. Southern blot analysis revealed that at least one copy of the transgene was integrated into the genome of the transgenic plants. Transgene expression was confirmed by Northern blot. CP4-EPSPS protein was detected by ELISA. Transgenic plants remained green and healthy when sprayed with Basta, containing 0.5% glufosinate ammonium or glyphosate. The optimized Agrobacterium-mediated transformation method resulted in an average of 9.4% transgenic plants. The results of the present study suggest that the optimized marker-free technique could be used as an effective and reliable method for routine transformation, which may facilitate the development of varieties of new antibiotic-free grass species.

Photosynthesis, water use, and root viability under water stress as affected by expression of SAG12-ipt controlling cytokinin synthesis in Agrostis stolonifera

Water stress reduces endogenous cytokinin (CK) content and may inhibit CK production. Maintenance of endogenous CK levels by genetic transformation with ipt in leaves and roots undergoing senescence may promote stress tolerance. This study was designed to determine the physiological effects of ipt expression on immature and mature leaves and in roots for plants exposed to different levels of water stress for creeping bentgrass (Agrostis stolonifera). Plants containing the ipt gene, encoding the enzyme adenine isopentenyl phosphotransferase for CK synthesis ligated to a senescence-activated promoter (SAG12), and wild-type 'Penncross' (WT) were grown hydroponically in a growth chamber and exposed to water stress by weekly additions of polyethylene glycol 8000 to reduce the growing solution osmotic potential from -0.05 to -0.3, -0.5, -0.7, -1.0, and -1.4 MPa. Immature and mature leaves and roots of SAG12-ipt creeping bentgrass were evaluated for ipt expression, CK content, leaf relative water content (RWC), chlorophyll content (Chl), photochemical efficiency (F(v)F(m)), osmotic adjustment (OA), photosynthesis rate (Pn), stomatal conductance (g(s)), transpiration (E), water use efficiency (WUE), carbon isotope discrimination (Δ), and root viability. Expression of ipt was detected in all plant parts and a higher CK content, primarily in the form of isopentyladenine (iPa), was found in SAG12-ipt plants but not in the WT plants under water stress. Immature leaves exhibited higher iPa and OA at all treatment levels. Mature leaves of SAG12-ipt plants maintained higher OA, Pn, Chl, WUE, and Δ, whereas g(s) and E were relatively unaffected compared to the WT. Roots of SAG12-ipt plants had higher levels of iPa and greater root viability than the WT. The results demonstrate that expression of ipt enhanced the tolerance of creeping bentgrass to water stress, which could be attributed to the positive effects on osmotic adjustment, efficient water use, and maintaining higher photosynthetic rate primarily for mature leaves, as well as increased root viability.

Proteomic changes associated with expression of a gene (ipt) controlling cytokinin synthesis for improving heat tolerance in a perennial grass species

Cytokinins (CKs) are known to regulate leaf senescence and affect heat tolerance, but mechanisms underlying CK regulation of heat tolerance are not well understood. A comprehensive proteomic study was conducted to identify proteins altered by the expression of the adenine isopentenyl transferase (ipt) gene controlling CK synthesis and associated with heat tolerance in transgenic plants for a C(3) perennial grass species, Agrostis stolonifera. Transgenic plants with two different inducible promoters (SAG12 and HSP18) and a null transformant (NT) containing the vector without ipt were exposed to 20 degrees C (control) or 35 degrees C (heat stress) in growth chambers. Two-dimensional electrophoresis and mass spectrometry analysis were performed to identify protein changes in leaves and roots in response to ipt expression under heat stress. Transformation with ipt resulted in protein changes in leaves and roots involved in multiple functions, particularly in energy metabolism, protein destination and storage, and stress defence. The abundance levels of six leaf proteins (enolase, oxygen-evolving enhancer protein 2, putative oxygen-evolving complex, Rubisco small subunit, Hsp90, and glycolate oxidase) and nine root proteins (Fd-GOGAT, nucleotide-sugar dehydratase, NAD-dependent isocitrate dehydrogenase, ferredoxin-NADP reductase precursor, putative heterogeneous nuclear ribonucleoprotein A2, ascorbate peroxidase, dDTP-glucose 4-6-dehydratases-like protein, and two unknown proteins) were maintained or increased in at least one ipt transgenic line under heat stress. The diversity of proteins altered in transgenic plants in response to heat stress suggests a regulatory role for CKs in various metabolic pathways associated with heat tolerance in C(3) perennial grass species.

The effect of the heterologous expression of Phragmites australis gamma-glutamylcysteine synthetase on the Cd2+ accumulation of Agrostis palustris

Heavy metal pollution has become one of the most serious environmental problems today. To develop a more efficient plant to clean up heavy metal contaminated soils, a gamma-glutamylcysteine synthetase (GCS) cDNA, named PaGCS, was isolated by PCR from Phragmites australis. The PaGCS sequence was transformed via agroinfection into the heavy metal intolerant grass Agrostis palustris. Five confirmed transgenic A. palustris plants expressing PaGCS were compared with the wild-type line for growth and Cd(2+) accumulation, as well as for the expression of a number of phytochelatin synthesis and stress-responsive enzymes when challenged with Cd(2+) stress. GCS and phytochelatin synthase (PCS) were up-regulated in the transgenic lines. All the transgenic lines accumulated more Cd(2+) and phytochelatins (PCs) than the wild-type line, and three of the five lines grew more effectively than the wild-type after either five or 21 d of Cd(2+) stress. Variation among the transgenics was observed for the distribution of Cd(2+) in the root, shoot and leaf. The malondialdehyde content of all the transgenic lines was lower than that of the wild type under Cd(2+) treatment, while the activity of both superoxide dismutase and peroxidase present in the transgenic lines increased markedly 24 h after Cd(2+) stress, and then rapidly declined.

Identification of heat stress-responsive genes in heat-adapted thermal Agrostis scabra by suppression subtractive hybridization

To gain insights into molecular mechanisms of grass tolerance to heat stress, we constructed a suppression subtractive cDNA library to identify heat-responsive genes for a C(3) grass species, thermal Agrostis scabra adapted to heat stress in geothermal areas in Yellowstone National Park. Plants were exposed to 20 degrees C (control) or 35 degrees C for 12d. The SSH analysis was performed with control samples as the driver and heat-stressed samples as the tester. Differentially expressed cDNA fragments were cloned to screen the heat up-regulated library. The SSH analysis identified 120 non-redundant putative heat-responsive cDNAs out of 1180 clones. Genes with homology to known proteins were categorized into six functional groups, with the largest group of genes involved in stress/defense, followed by the group of genes related to protein metabolism. Immunoblot analysis confirmed increases in transcripts of selected genes under heat stress. Transcripts of seven and eight genes were strongly enhanced or induced in shoots and roots, respectively, while two genes were only induced in roots under heat stress. The heat up-regulated genes in thermal A. scabra adapted to long-term heat stress are potential candidate genes for engineering stress-tolerant grasses and for revealing molecular mechanisms of grass adaptation to heat stress.

Production of purple-colored creeping bentgrass using maize transcription factor genes Pl and Lc through Agrobacterium-mediated transformation

Purple-colored transgenic creeping bentgrass (Agrostis stolonifera L.) plants were developed for ornamental purpose by means of Agrobacterium-mediated transformation. Embryogenic creeping bentgrass calli were transformed with the pCAMBIA 3301 vector harboring maize (Zea mays) flavonoid/anthocyanin biosynthetic pathway transcription factor genes, Lc (Leaf color) and Pl (Purple leaf), individually and in combination, and three types of putative transgenic plants (Lc, Pl, and Lc + Pl) were generated. Genomic integration and expression of the transgenes were confirmed by Southern and northern blot analyses, respectively. The transgenic creeping bentgrass plants expressing both Lc and Pl genes were entirely purple, whereas those expressing Pl alone had purple stems and those expressing Lc alone lacked purple pigmentation in adult plants. The anthocyanin content was estimated in all the three types of transgenic plant and correlated well with the degree of purple coloration observed. These results suggest that both Lc and Pl genes are necessary and sufficient to confer purple coloration to creeping bentgrass.

Analysis of expressed sequence tags (ESTs) from Agrostis species obtained using sequence related amplified polymorphism

Bentgrass (Agrostis spp.), a genus of the Poaceae family, consists of more than 200 species and is mainly used in athletic fields and golf courses. Creeping bentgrass (A. stolonifera L.) is the most commonly used species in maintaining golf courses, followed by colonial bentgrass (A. capillaris L.) and velvet bentgrass (A. canina L.). The presence and nature of sequence related amplified polymorphism (SRAP) at the cDNA level were investigated. We isolated 80 unique cDNA fragment bands from these species using 56 SRAP primer combinations. Sequence analysis of cDNA clones and analysis of putative translation products revealed that some encoded amino acid sequences were similar to proteins involved in DNA synthesis, transcription, and signal transduction. The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene (GenBank accession no. EB812822) was also identified from velvet bentgrass, and the corresponding protein sequence is further analyzed due to its critical role in many cellular processes. The partial peptide sequence obtained was 112 amino acids long, presenting a high degree of homology to parts of the N-terminal and C-terminal regions of cytosolic phosphorylating GAPDH (GapC). The existence of common expressed sequence tags (ESTs) revealed by a minimum evolutionary dendrogram among the Agrostis ESTs indicated the usefulness of SRAP for comparative genome analysis of transcribed genes in the grass species.

Root proteomic responses to heat stress in two Agrostis grass species contrasting in heat tolerance

Protein metabolism plays an important role in plant adaptation to heat stress. This study was designed to identify heat-responsive proteins in roots associated with thermotolerance for two C3 grass species contrasting in heat tolerance, thermal Agrostis scabra and heat-sensitive Agrostis stolonifera L. Plants were exposed to 20 degrees C (control), 30 C (moderate heat stress), or 40 degrees C (severe heat stress) in growth chambers. Roots were harvested at 2 d and 10 d after temperature treatment. Proteins were extracted and separated by two-dimensional polyacrylamide gel electrophoresis. Seventy protein spots were regulated by heat stress in at least one species. Under both moderate and severe heat stress, more proteins were down-regulated than were up-regulated, and thermal A. scabra roots had more up-regulated proteins than A. stolonifera roots. The sequences of 66 differentially expressed protein spots were identified using mass spectrometry. The results suggested that the up-regulation of sucrose synthase, glutathione S-transferase, superoxide dismutase, and heat shock protein Sti (stress-inducible protein) may contribute to the superior root thermotolerance of A. scabra. In addition, phosphoproteomic analysis indicated that two isoforms of fructose-biphosphate aldolase were highly phosphorylated under heat stress, and thermal A. scabra had greater phosphorylation than A. stolonifera, suggesting that the aldolase phosphorylation might be involved in root thermotolerance.

Identification and characterization of an expansin gene AsEXP1 associated with heat tolerance in C3 Agrostis grass species

Plant tolerance of heat stress involves various changes at physiological and molecular levels. The objective of this study was to examine the expression of a gene encoding expansin protein in relation to heat tolerance in two C(3) grass species and genotypes differing in heat tolerance. Heat-tolerant, thermal Agrostis scabra, adapted to high temperatures in geothermal areas in Yellowstone National Park, was subjected to 20 degrees C (control) or 40 degrees C (heat stress) for 7 d in a growth chamber. Differential display analysis identified that a gene, AsEXP1, encoding an expansin protein, was strongly up-regulated in leaves exposed to heat stress in thermal A. scabra. Virtual northern hybridization and RT-PCR confirmed that AsEXP1 was a heat-inducible gene in leaves. The expression of AsEXP1 was induced at 1 h of plant exposure to heat stress and reached the highest level of expression at 4 h of treatment. A 1.3 kb full-length cDNA of AsEXP1 was isolated, which encodes a 251 amino acid protein. Two ecotypes of thermal A. scabra and 10 genotypes of Agrostis stolonifera (creeping bentgrass), a widely used turfgrass species in cool climatic regions, varying in the level of heat tolerance, were exposed to 40 degrees C for 7 d to examine the level of AsEXP1 expression in relation to heat tolerance. Genetic variation in heat tolerance was evaluated by measuring cell membrane stability, photochemical efficiency, and leaf growth. RT-PCR analysis revealed that the level of AsEXP1 in different genotypes was positively correlated with the level of heat tolerance in both grass species. The results first identified a heat-related expansin gene in grass species and suggest that AsEXP1 may be useful as a molecular marker to select for heat-tolerant grass germplasm.

Complete chloroplast genome sequences of Hordeum vulgare, Sorghum bicolor and Agrostis stolonifera, and comparative analyses with other grass genomes

Comparisons of complete chloroplast genome sequences of Hordeum vulgare, Sorghum bicolor and Agrostis stolonifera to six published grass chloroplast genomes reveal that gene content and order are similar but two microstructural changes have occurred. First, the expansion of the IR at the SSC/IRa boundary that duplicates a portion of the 5' end of ndhH is restricted to the three genera of the subfamily Pooideae (Agrostis, Hordeum and Triticum). Second, a 6 bp deletion in ndhK is shared by Agrostis, Hordeum, Oryza and Triticum, and this event supports the sister relationship between the subfamilies Erhartoideae and Pooideae. Repeat analysis identified 19-37 direct and inverted repeats 30 bp or longer with a sequence identity of at least 90%. Seventeen of the 26 shared repeats are found in all the grass chloroplast genomes examined and are located in the same genes or intergenic spacer (IGS) regions. Examination of simple sequence repeats (SSRs) identified 16-21 potential polymorphic SSRs. Five IGS regions have 100% sequence identity among Zea mays, Saccharum officinarum and Sorghum bicolor, whereas no spacer regions were identical among Oryza sativa, Triticum aestivum, H. vulgare and A. stolonifera despite their close phylogenetic relationship. Alignment of EST sequences and DNA coding sequences identified six C-U conversions in both Sorghum bicolor and H. vulgare but only one in A. stolonifera. Phylogenetic trees based on DNA sequences of 61 protein-coding genes of 38 taxa using both maximum parsimony and likelihood methods provide moderate support for a sister relationship between the subfamilies Erhartoideae and Pooideae.

Complete chloroplast genome sequences of Hordeum vulgare, Sorghum bicolor and Agrostis stolonifera, and comparative analyses with other grass genomes

Comparisons of complete chloroplast genome sequences of Hordeum vulgare, Sorghum bicolor and Agrostis stolonifera to six published grass chloroplast genomes reveal that gene content and order are similar but two microstructural changes have occurred. First, the expansion of the IR at the SSC/IRa boundary that duplicates a portion of the 5' end of ndhH is restricted to the three genera of the subfamily Pooideae (Agrostis, Hordeum and Triticum). Second, a 6 bp deletion in ndhK is shared by Agrostis, Hordeum, Oryza and Triticum, and this event supports the sister relationship between the subfamilies Erhartoideae and Pooideae. Repeat analysis identified 19-37 direct and inverted repeats 30 bp or longer with a sequence identity of at least 90%. Seventeen of the 26 shared repeats are found in all the grass chloroplast genomes examined and are located in the same genes or intergenic spacer (IGS) regions. Examination of simple sequence repeats (SSRs) identified 16-21 potential polymorphic SSRs. Five IGS regions have 100% sequence identity among Zea mays, Saccharum officinarum and Sorghum bicolor, whereas no spacer regions were identical among Oryza sativa, Triticum aestivum, H. vulgare and A. stolonifera despite their close phylogenetic relationship. Alignment of EST sequences and DNA coding sequences identified six C-U conversions in both Sorghum bicolor and H. vulgare but only one in A. stolonifera. Phylogenetic trees based on DNA sequences of 61 protein-coding genes of 38 taxa using both maximum parsimony and likelihood methods provide moderate support for a sister relationship between the subfamilies Erhartoideae and Pooideae.