Overexpression of barley hva1 gene in creeping bentgrass for improving drought tolerance

Gene pyramiding for boosted plant growth and broad abiotic stress tolerance

Abiotic stresses such as salinity, heat and drought seriously impair plant growth and development, causing a significant loss in crop yield and ornamental value. Biotechnology approaches manipulating specific genes prove to be effective strategies in crop trait modification. The Arabidopsis vacuolar pyrophosphatase gene AVP1, the rice SUMO E3 ligase gene OsSIZ1 and the cyanobacterium flavodoxin gene Fld have previously been implicated in regulating plant stress responses and conferring enhanced tolerance to different abiotic stresses when individually overexpressed in various plant species. We have explored the feasibility of combining multiple favourable traits brought by individual genes to acquire superior plant performance. To this end, we have simultaneously introduced AVP1, OsSIZ1 and Fld in creeping bentgrass. Transgenic (TG) plants overexpressing these three genes performed significantly better than wild type controls and the TGs expressing individual genes under both normal and various abiotic stress conditions, exhibited significantly enhanced plant growth and tolerance to drought, salinity and heat stresses as well as nitrogen and phosphate starvation, which were associated with altered physiological and biochemical characteristics and delicately fine-tuned expression of genes involved in plant stress responses. Our results suggest that AVP1, OsSIZ1 and Fld function synergistically to regulate plant development and plant stress response, leading to superior overall performance under both normal and adverse environments. The information obtained provides new insights into gene stacking as an effective approach for plant genetic engineering. A similar strategy can be extended for the use of other beneficial genes in various crop species for trait modifications, enhancing agricultural production.

Overexpression of HVA1 Enhances Drought and Heat Stress Tolerance in Triticum aestivum Doubled Haploid Plants

Plant responses to multiple environmental stresses include various signaling pathways that allow plant acclimation and survival. Amongst different stresses, drought and heat stress severely affect growth and productivity of wheat. HVA1, a member of the group 3 LEA protein, has been well known to provide protection against drought stress. However, its mechanism of action and its role in other stresses such as heat remain unexplored. In this study, doubled haploid (DH) wheat plants overexpressing the HVA1 gene were analyzed and found to be both drought-and heat stress-tolerant. The transcriptome analysis revealed the upregulation of transcription factors such as DREB and HsfA6 under drought and heat stress, respectively, which contribute toward the tolerance mechanism. Particularly under heat stress conditions, the transgenic plants had a lower oxidative load and showed enhanced yield. The overexpression lines were found to be ABA-sensitive, therefore suggesting the role of HsfA6 in providing heat tolerance via the ABA-mediated pathway. Thus, apart from its known involvement in drought stress, this study highlights the potential role of HVA1 in the heat stress signaling pathway. This can further facilitate the engineering of multiple stress tolerance in crop plants, such as wheat.

A High-Density Genetic Linkage Map of SLAFs and QTL Analysis of Grain Size and Weight in Barley (Hordeum vulgare L.)

Grain size is an important agronomic trait determines yield in barley, and a high-density genetic map is helpful to accurately detect quantitative trait loci (QTLs) related to grain traits. Using specific-locus amplified fragment sequencing (SLAF-seq) technology, a high-density genetic map was constructed with a population of 134 recombinant inbred lines (RILs) deriving from a cross between Golden Promise (GP) and H602, which contained 12,635 SLAFs with 26,693 SNPs, and spanned 896.74 cM with an average interval of 0.07 cM on seven chromosomes. Based on the map, a total of 16 QTLs for grain length (GL), grain width and thousand-grain weight were detected on 1H, 2H, 4H, 5H, and 6H. Among them, a major QTL locus qGL1, accounting for the max phenotypic variance of 16.7% was located on 1H, which is a new unreported QTL affecting GL. In addition, the other two QTLs, qGL5 and qTGW5, accounting for the max phenotypic variances of 20.7 and 21.1%, respectively, were identified in the same region, and sequencing results showed they are identical to HvDep1 gene. These results indicate that it is a feasible approach to construct a high-quality genetic map for QTL mapping by using SLAF markers, and the detected major QTLs qGL1, qGL5, and qTGW5 are useful for marker-assisted selection (MAS) of grain size in barley breeding.

Dissecting the Genomic Diversification of Late Embryogenesis Abundant (LEA) Protein Gene Families in Plants

Late embryogenesis abundant (LEA) proteins include eight multigene families that are expressed in response to water loss during seed maturation and in vegetative tissues of desiccation tolerant species. To elucidate LEA proteins evolution and diversification, we performed a comprehensive synteny and phylogenetic analyses of the eight gene families across 60 complete plant genomes. Our integrated comparative genomic approach revealed that synteny conservation and diversification contributed to LEA family expansion and functional diversification in plants. We provide examples that: 1) the genomic diversification of the Dehydrin family contributed to differential evolution of amino acid sequences, protein biochemical properties, and gene expression patterns, and led to the appearance of a novel functional motif in angiosperms; 2) ancient genomic diversification contributed to the evolution of distinct intrinsically disordered regions of LEA_1 proteins; 3) recurrent tandem-duplications contributed to the large expansion of LEA_2; and 4) dynamic synteny diversification played a role on the evolution of LEA_4 and its function on plant desiccation tolerance. Taken together, these results show that multiple evolutionary mechanisms have not only led to genomic diversification but also to structural and functional plasticity among LEA proteins which have jointly contributed to the adaptation of plants to water-limiting environments.

The dehydration stress of couch grass is associated with its lipid metabolism, the induction of transporters and the re-programming of development coordinated by ABA

Background

The wild relatives of crop species represent a potentially valuable source of novel genetic variation, particularly in the context of improving the crop’s level of tolerance to abiotic stress. The mechanistic basis of these tolerances remains largely unexplored. Here, the focus was to characterize the transcriptomic response of the nodes (meristematic tissue) of couch grass (a relative of barley) to dehydration stress, and to compare it to that of the barley crown formed by both a drought tolerant and a drought sensitive barley cultivar.

Results

Many of the genes up-regulated in the nodes by the stress were homologs of genes known to be mediated by abscisic acid during the response to drought, or were linked to either development or lipid metabolism. Transporters also featured prominently, as did genes acting on root architecture. The resilience of the couch grass node arise from both their capacity to develop an altered, more effective root architecture, but also from their formation of a lipid barrier on their outer surface and their ability to modify both their lipid metabolism and transporter activity when challenged by dehydration stress.

Conclusions

Our analysis revealed the nature of dehydration stress response in couch grass. We suggested the tolerance is associated with lipid metabolism, the induction of transporters and the re-programming of development coordinated by ABA. We also proved the applicability of barley microarray for couch grass stress-response analysis.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4700-3) contains supplementary material, which is available to authorized users.

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.

Overexpression of a novel cold-responsive transcript factor LcFIN1 from sheepgrass enhances tolerance to low temperature stress in transgenic plants

As a perennial forage crop broadly distributed in eastern Eurasia, sheepgrass (Leymus chinensis (Trin.) Tzvel) is highly tolerant to low-temperature stress. Previous report indicates that sheepgrass is able to endure as low as -47.5 °C,allowing it to survive through the cold winter season. However, due to the lack of sufficient studies, the underlying mechanism towards the extraordinary low-temperature tolerance is unclear. Although the transcription profiling has provided insight into the transcriptome response to cold stress, more detailed studies are required to dissect the molecular mechanism regarding the excellent abiotic stress tolerance. In this work, we report a novel transcript factor LcFIN1 (L. chinensis freezing-induced 1) from sheepgrass. LcFIN1 showed no homology with other known genes and was rapidly and highly induced by cold stress, suggesting that LcFIN1 participates in the early response to cold stress. Consistently, ectopic expression of LcFIN1 significantly increased cold stress tolerance in the transgenic plants, as indicated by the higher survival rate, fresh weight and other stress-related indexes after a freezing treatment. Transcriptome analysis showed that numerous stress-related genes were differentially expressed in LcFIN1-overexpressing plants, suggesting that LcFIN1 may enhance plant abiotic stress tolerance by transcriptional regulation. Electrophoretic mobility shift assays and CHIP-qPCR showed that LcCBF1 can bind to the CRT/DRE cis-element located in the promoter region of LcFIN1, suggesting that LcFIN1 is directly regulated by LcCBF1. Taken together, our results suggest that LcFIN1 positively regulates plant adaptation response to cold stress and is a promising candidate gene to improve crop cold tolerance.

Expression profiling of genes involved in drought stress and leaf senescence in juvenile barley

BACKGROUND

Drought stress in juvenile stages of crop development and premature leaf senescence induced by drought stress have an impact on biomass production and yield formation of barley (Hordeum vulgare L.). Therefore, in order to get information of regulatory processes involved in the adaptation to drought stress and leaf senescence expression analyses of candidate genes were conducted on a set of 156 barley genotypes in early developmental stages, and expression quantitative trait loci (eQTL) were identified by a genome wide association study.

RESULTS

Significant effects of genotype and treatment were detected for leaf colour measured at BBCH 25 as an indicator of leaf senescence and for the expression level of the genes analysed. Furthermore, significant correlations were detected within the group of genes involved in drought stress (r = 0.84) and those acting in leaf senescence (r = 0.64), as well as between leaf senescence genes and the leaf colour (r = 0.34). Based on these expression data and 3,212 polymorphic single nucleotide polymorphisms (SNP) with a minor allele frequency >5% derived from the Illumina 9 k iSelect SNP Chip, eight cis eQTL and seven trans eQTL were found. Out of these an eQTL located on chromosome 3H at 142.1 cM is of special interest harbouring two drought stress genes (GAD3 and P5CS2) and one leaf senescence gene (Contig7437), as well as an eQTL on chromosome 5H at 44.5 cM in which two genes (TRIUR3 and AVP1) were identified to be associated to drought stress tolerance in a previous study.

CONCLUSION

With respect to the expression of genes involved in drought stress and early leaf senescence, genotypic differences exist in barley. Major eQTL for the expression of these genes are located on barley chromosome 3H and 5H. Respective markers may be used in future barley breeding programmes for improving tolerance to drought stress and leaf senescence.

The TaDREB3 transgene transferred by conventional crossings to different genetic backgrounds of bread wheat improves drought tolerance

Drought tolerance of the wheat cultivar Bobwhite was previously enhanced by transformation with a construct containing the wheat DREB3 gene driven by the stress-inducible maize Rab17 promoter. Progeny of a single T2 transgenic line were used as pollinators in crosses with four elite bread wheat cultivars from Western Australia: Bonnie Rock, IGW-2971, Magenta and Wyalkatchem, with the aim of evaluating transgene performance in different genetic backgrounds. The selected pollinator line, BW8-9-10-3, contained multiple transgene copies, had significantly improved drought tolerance compared with wild-type plants and showed no growth and development penalties or abnormalities. A single hybrid plant was selected from each cross-combination for three rounds of backcrossing with the corresponding maternal wheat cultivar. The transgene was detected in all four F1 BC3 combinations, but stress-inducible transgene expression was found in only three of the four combinations. Under well-watered conditions, the phenotypes and grain yield components of the F2 BC3 transgene-expressing lines were similar to those of corresponding recurrent parents and null-segregants. Under severe drought conditions, the backcross lines demonstrated 12-18% higher survival rates than the corresponding control plants. Two from four F3 BC3 transgenic lines showed significantly higher yield (18.9% and 21.5%) than control plants under limited water conditions. There was no induction of transgene expression under cold stress, and therefore, no improvement of frost tolerance observed in the progenies of drought-tolerant F3 BC3 lines.

Barley Genes as Tools to Confer Abiotic Stress Tolerance in Crops

Barley is one of the oldest cultivated crops in the world with a high adaptive capacity. The natural tolerance of barley to stress has led to increasing interest in identification of stress responsive genes through small/large-scale omics studies, comparative genomics, and overexpression of some of these genes by genetic transformation. Two major categories of proteins involved in stress tolerance are transcription factors (TFs) responsible from the re-programming of the metabolism in stress environment, and genes encoding Late Embryogenesis Abundant (LEA) proteins, antioxidant enzymes, osmolytes, and transporters. Constitutive overexpression of several barley TFs, such as C-repeat binding factors (HvCBF4), dehydration-responsive element-binding factors (HvDREB1), and WRKYs (HvWRKY38), in transgenic plants resulted in higher tolerance to drought and salinity, possibly by effectively altering the expression levels of stress tolerance genes due to their higher DNA binding affinity. Na(+)/H(+) antiporters, channel proteins, and lipid transporters can also be the strong candidates for engineering plants for tolerance to salinity and low temperatures.

A late embryogenesis abundant protein HVA1 regulated by an inducible promoter enhances root growth and abiotic stress tolerance in rice without yield penalty

Regulation of root architecture is essential for maintaining plant growth under adverse environment. A synthetic abscisic acid (ABA)/stress-inducible promoter was designed to control the expression of a late embryogenesis abundant protein (HVA1) in transgenic rice. The background of HVA1 is low but highly inducible by ABA, salt, dehydration and cold. HVA1 was highly accumulated in root apical meristem (RAM) and lateral root primordia (LRP) after ABA/stress treatments, leading to enhanced root system expansion. Water-use efficiency (WUE) and biomass also increased in transgenic rice, likely due to the maintenance of normal cell functions and metabolic activities conferred by HVA1 which is capable of stabilizing proteins, under osmotic stress. HVA1 promotes lateral root (LR) initiation, elongation and emergence and primary root (PR) elongation via an auxin-dependent process, particularly by intensifying asymmetrical accumulation of auxin in LRP founder cells and RAM, even under ABA/stress-suppressive conditions. We demonstrate a successful application of an inducible promoter in regulating the spatial and temporal expression of HVA1 for improving root architecture and multiple stress tolerance without yield penalty.

Overexpression of AtDREB1D transcription factor improves drought tolerance in soybean

Drought is one of the major abiotic stresses that affect productivity in soybean (Glycine max L.) Several genes induced by drought stress include functional genes and regulatory transcription factors. The Arabidopsis thaliana DREB1D transcription factor driven by the constitutive and ABA-inducible promoters was introduced into soybean through Agrobacterium tumefaciens-mediated gene transfer. Several transgenic lines were generated and molecular analysis was performed to confirm transgene integration. Transgenic plants with an ABA-inducible promoter showed a 1.5- to two-fold increase of transgene expression under severe stress conditions. Under well-watered conditions, transgenic plants with constitutive and ABA-inducible promoters showed reduced total leaf area and shoot biomass compared to non-transgenic plants. No significant differences in root length or root biomass were observed between transgenic and non-transgenic plants under non-stress conditions. When subjected to gradual water deficit, transgenic plants maintained higher relative water content because the transgenic lines used water more slowly as a result of reduced total leaf area. This caused them to wilt slower than non-transgenic plants. Transgenic plants showed differential drought tolerance responses with a significantly higher survival rate compared to non-transgenic plants when subjected to comparable severe water-deficit conditions. Moreover, the transgenic plants also showed improved drought tolerance by maintaining 17-24 % greater leaf cell membrane stability compared to non-transgenic plants. The results demonstrate the feasibility of engineering soybean for enhanced drought tolerance by expressing stress-responsive genes.

Optimization of TaDREB3 gene expression in transgenic barley using cold-inducible promoters

Constitutive over-expression of the TaDREB3 gene in barley improved frost tolerance of transgenic plants at the vegetative stage of plant development, but leads to stunted phenotypes and 3- to 6-week delays in flowering compared to control plants. In this work, two cold-inducible promoters with contrasting properties, the WRKY71 gene promoter from rice and the Cor39 gene promoter from durum wheat, were applied to optimize expression of TaDREB3. The aim of the work was to increase plant frost tolerance and to decrease or prevent negative developmental phenotypes observed during constitutive expression of TaDREB3. The OsWRKY71 and TdCor39 promoters had low-to-moderate basal activity and were activated by cold treatment in leaves, stems and developing spikes of transgenic barley and rice. Expression of the TaDREB3 gene, driven by either of the tested promoters, led to a significant improvement in frost tolerance. The presence of the functional TaDREB3 protein in transgenic plants was confirmed by the detection of strong up-regulation of cold-responsive target genes. The OsWRKY71 promoter-driven TaDREB3 provides stronger activation of the same target genes than the TdCor39 promoter. Analysis of the development of transgenic plants in the absence of stress revealed small or no differences in plant characteristics and grain yield compared with wild-type plants. The WRKY71-TaDREB3 promoter-transgene combination appears to be a promising tool for the enhancement of cold and frost tolerance in crop plants but field evaluation will be needed to confirm that negative development phenotypes have been controlled.

Biotechnological approaches to study plant responses to stress

Multiple biotic and abiotic environmental stress factors affect negatively various aspects of plant growth, development, and crop productivity. Plants, as sessile organisms, have developed, in the course of their evolution, efficient strategies of response to avoid, tolerate, or adapt to different types of stress situations. The diverse stress factors that plants have to face often activate similar cell signaling pathways and cellular responses, such as the production of stress proteins, upregulation of the antioxidant machinery, and accumulation of compatible solutes. Over the last few decades advances in plant physiology, genetics, and molecular biology have greatly improved our understanding of plant responses to abiotic stress conditions. In this paper, recent progresses on systematic analyses of plant responses to stress including genomics, proteomics, metabolomics, and transgenic-based approaches are summarized.

Is genetic engineering ever going to take off in forage, turf and bioenergy crop breeding?

BACKGROUND

Genetic engineering offers the opportunity to generate unique genetic variation that is either absent in the sexually compatible gene pool or has very low heritability. The generation of transgenic plants, coupled with breeding, has led to the production of widely used transgenic cultivars in several major cash crops, such as maize, soybean, cotton and canola. The process for regulatory approval of genetically engineered crops is slow and subject to extensive political interference. The situation in forage grasses and legumes is more complicated.

SCOPE

Most widely grown forage, turf and bioenergy species (e.g. tall fescue, perennial ryegrass, switchgrass, alfalfa, white clover) are highly self-incompatible and outcrossing. Compared with inbreeding species, they have a high potential to pass their genes to adjacent plants. A major biosafety concern in these species is pollen-mediated transgene flow. Because human consumption is indirect, risk assessment of transgenic forage, turf and bioenergy species has focused on their environmental or ecological impacts. Although significant progress has been made in genetic modification of these species, commercialization of transgenic cultivars is very limited because of the stringent and costly regulatory requirements. To date, the only transgenic forage crop deregulated in the US is 'Roundup Ready' (RR) alfalfa. The approval process for RR alfalfa was complicated, involving several rounds of regulation, deregulation and re-regulation. Nevertheless, commercialization of RR alfalfa is an important step forward in regulatory approval of a perennial outcrossing forage crop. As additional transgenic forage, turf and bioenergy crops are generated and tested, different strategies have been developed to meet regulatory requirements. Recent progress in risk assessment and deregulation of transgenic forage and turf species is summarized and discussed.

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.

Agrobacterium-mediated transformation of Sorghum bicolor using immature embryos

Successful efforts describing in vitro culturing, regeneration, and transformation of grain sorghum were reported, using particle bombardment, as early as 1993, and with Agrobacterium tumefaciens in 2000. Reported transformation efficiencies via Agrobacterium routinely range from 1 to 2%. Recently, such efficiencies via Agrobacterium in several plant species were improved with the use of heat and centrifugation treatments of explants prior to infection. Here, we describe the successful use of heat pretreatment of immature embryos (IEs) prior to Agrobacterium inoculation to increase routine transformation frequencies of a single genotype, P898012, to greater than 7%. This reproducible frequency was calculated as numbers of independently transformed IEs, confirmed by PCR, western, and DNA hybridization analysis, that produced fertile transgenic plants, divided by total numbers of infected IEs.

Stress-inducible expression of barley Hva1 gene in transgenic mulberry displays enhanced tolerance against drought, salinity and cold stress

Coping with different kinds of biotic and abiotic stresses is the foundation of sustainable agriculture. Although conventional breeding and marker-assisted selection are being employed in mulberry (Morus indica L.) to develop better varieties, nonetheless the longer time periods required for these approaches necessitates the use of precise biotechnological approaches for sustainable agriculture. In an attempt to improve stress tolerance of mulberry, an important plant of the sericulture industry, an encoding late embryogenesis abundant gene from barley (HVA1) was introduced into mulberry plants by Agrobacterium-mediated transformation. Transgenic mulberry with barley Hva1 under a constitutive promoter actin1 was shown to enhance drought and salinity tolerance. Here, we report that overexpression of barley Hva1 also confers cold tolerance in transgenic mulberry. Further, barley Hva1 gene under control of a stress-inducible promoter rd29A can effectively negate growth retardation under non-stress conditions and confer stress tolerance in transgenic mulberry. Transgenic lines display normal morphology to enhanced growth and an increased tolerance against drought, salt and cold conditions as measured by free proline, membrane stability index and PSII activity. Protein accumulation was detected under stress conditions confirming inductive expression of HVA1 in transgenics. Investigations to assess stress tolerance of these plants under field conditions revealed an overall better performance than the non-transgenic plants. Enhanced expression of stress responsive genes such as Mi dnaJ and Mi 2-cysperoxidin suggests that Hva1 can regulate downstream genes associated with providing abiotic stress tolerance. The investigation of transgenic lines presented here demonstrates the acquisition of tolerance against drought, salt and cold stress in plants overexpressing barley Hva1, indicating that Arabidopsis rd29A promoter can function in mulberry.

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.

Membrane transport, sensing and signaling in plant adaptation to environmental stress

Plants are generally well adapted to a wide range of environmental conditions. Even though they have notably prospered in our planet, stressful conditions such as salinity, drought and cold or heat, which are increasingly being observed worldwide in the context of the ongoing climate changes, limit their growth and productivity. Behind the remarkable ability of plants to cope with these stresses and still thrive, sophisticated and efficient mechanisms to re-establish and maintain ion and cellular homeostasis are involved. Among the plant arsenal to maintain homeostasis are efficient stress sensing and signaling mechanisms, plant cell detoxification systems, compatible solute and osmoprotectant accumulation and a vital rearrangement of solute transport and compartmentation. The key role of solute transport systems and signaling proteins in cellular homeostasis is addressed in the present work. The full understanding of the plant cell complex defense mechanisms under stress may allow for the engineering of more tolerant plants or the optimization of cultivation practices to improve yield and productivity, which is crucial at the present time as food resources are progressively scarce.

The advent of genomics in mulberry and perspectives for productivity enhancement

Sericulture in India is a highly remunerative industry, especially for the rural population. Mulberry is an extremely versatile plant, having multifaceted applications, the most important being the sole feed for the monophagus silkworm, Bombyx mori. Profitability of the sericulture industry is directly correlated with production of high-quality mulberry leaves. However, mulberry productivity is severely impacted by abiotic as well as biotic stresses. Therefore, to develop stress-tolerant mulberry with desired characteristics, a comprehensive understanding and utility of biotechnological resources is essential. Research efforts on mulberry encompass broad range of fields in plant biology from breeding, molecular markers, transcriptomics, proteomics, and metabolomics. Additionally, a large number of mulberry germplasm accessions have been maintained and evaluated in several countries. Identification of superior cultivars under stressed regimes is extremely important, and therefore, physiological traits have often been used as proxy genetic markers for assessing stress tolerance index. Mulberry genomic resources have provided a limited but an important list of novel candidate genes, thus enhancing the scope for future investigations for improvement of its productivity. The present review article gives a bird's eye view of current initiatives of genomics advancements in mulberry research and enumerates the prospects for enhancing its productivity.

Differential proteomic responses to water stress induced by PEG in two creeping bentgrass cultivars differing in stress tolerance

Protein metabolism and expression play important role in plant adaptation to water stress. The objectives of this study were to examine proteomic responses to water stress induced by polyethylene glycol (PEG) in creeping bentgrass (Agrostis stolonifera L.) leaves and to identify proteins associated with stress tolerance. Plants of two cultivars ('Penncross' and 'Penn-A4') differing in water stress tolerance were grown in sand irrigated daily with water (control) or PEG solution (osmotic potential of -0.66MPa) to induce water stress, for 28d in growth chambers. Shoot extension rate, relative water content and cell membrane stability were measured to compare drought tolerance between the two cultivars. All parameters maintained at a significantly higher level in 'Penn-A4' than in 'Penncross' under PEG treatment. After 28d of water stress, proteins were extracted from leaves and separated by difference gel electrophoresis. Among 56 stress-responsive protein spots, 46 were identified using mass spectrometry. Some proteins involved in primary nitrogen and carbon metabolism were down-regulated by PEG-induced water stress in both cultivars. The abundance of antioxidant enzyme proteins (ascorbate peroxidase, catalase and glutathione-S-transferase) increased under water stress, particularly ascorbate peroxidase in 'Penn-A4'. The abundance levels of actins, UDP-sulfoquinovose synthase and glucan exohydrolase were greater in 'Penn-A4' than in 'Penncross' under PEG treatment. Our results suggest that proteins involved in membrane synthesis, cell wall loosening, cell turgor maintenance, and antioxidant defense may play roles in perennial grass adaptation to PEG-induced water stress.

Functional analysis of the group 4 late embryogenesis abundant proteins reveals their relevance in the adaptive response during water deficit in Arabidopsis

Late-Embryogenesis Abundant (LEA) proteins accumulate to high levels during the last stages of seed development, when desiccation tolerance is acquired, and in vegetative and reproductive tissues under water deficit, leading to the hypothesis that these proteins play a role in the adaptation of plants to this stress condition. In this work, we obtained the accumulation patterns of the Arabidopsis (Arabidopsis thaliana) group 4 LEA proteins during different developmental stages and plant organs in response to water deficit. We demonstrate that overexpression of a representative member of this group of proteins confers tolerance to severe drought in Arabidopsis plants. Moreover, we show that deficiency of LEA proteins in this group leads to susceptible phenotypes upon water limitation, during germination, or in mature plants after recovery from severe dehydration. Upon recovery from this stress condition, mutant plants showed a reduced number of floral and axillary buds when compared with wild-type plants. The lack of these proteins also correlates with a reduced seed production under optimal irrigation, supporting a role in fruit and/or seed development. A bioinformatic analysis of group 4 LEA proteins from many plant genera showed that there are two subgroups, originated through ancient gene duplication and a subsequent functional specialization. This study represents, to our knowledge, the first genetic evidence showing that one of the LEA protein groups is directly involved in the adaptive response of higher plants to water deficit, and it provides data indicating that the function of these proteins is not redundant to that of the other LEA proteins.

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.

Cloning and genetic diversity analysis of a new P5CS gene from common bean (Phaseolus vulgaris L.)

Delta(1)-pyrroline-5-carboxylate synthetase (P5CS) is the rate-limiting enzyme involved in the biosynthesis of proline in plants. By the 3' rapid amplification of cDNA ends (3'-RACE) approach, a 2,246-bp cDNA sequence was obtained from common bean (Phaseolus vulgaris L.), denominated PvP5CS2 differing from another P5CS gene that we cloned previously from common bean (PvP5CS). The predicted amino acid sequence of PvP5CS2 has an overall 93.2% identity GmP5CS (Glycine max L. P5CS). However, PvP5CS2 shows only 83.7% identity in amino acid sequence to PvP5CS, suggesting PvP5CS2 represents a homolog of the soybean P5CS gene. Abundant indel (insertion and deletion events) and SNP (single nucleotide polymorphisms) were found in the cloned PvP5CS2 genome sequence when comparing 24 cultivated and 3 wild common bean accessions and these in turn reflected aspects of common bean evolution. Sequence alignment showed that genotypes from the same gene pool had similar nucleotide variation, while genotypes from different gene pools had distinctly different nucleotide variation for PvP5CS2. Furthermore, diversity along the gene sequence was not evenly distributed, being low in the glutamic-g-semialdehyde dehydrogenase catalyzing region, moderate in the Glu-5-kinase catalyzing region and high in the intervening region. Neutrality tests showed that PvP5CS2 was a conserved gene undergoing negative selection. A new marker (Pv97) was developed for genetic mapping of PvP5CS2 based on an indel between DOR364 and G19833 sequences and the gene was located between markers Bng126 and BMd045 on chromosome b01. The relationship of PvP5CS2 and a previously cloned pyrroline-5-carboxylate synthetase gene as well as the implications of this work on selecting for drought tolerance in common bean are discussed.

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.

A simple and sensitive high-throughput GFP screening in woody and herbaceous plants

Green fluorescent protein (GFP) has been used widely as a powerful bioluminescent reporter, but its visualization by existing methods in tissues or whole plants and its utilization for high-throughput screening remains challenging in many species. Here, we report a fluorescence image analyzer-based method for GFP detection and its utility for high-throughput screening of transformed plants. Of three detection methods tested, the Typhoon fluorescence scanner was able to detect GFP fluorescence in all Arabidopsis thaliana tissues and apple leaves, while regular fluorescence microscopy detected it only in Arabidopsis flowers and siliques but barely in the leaves of either Arabidopsis or apple. The hand-held UV illumination method failed in all tissues of both species. Additionally, the Typhoon imager was able to detect GFP fluorescence in both green and non-green tissues of Arabidopsis seedlings as well as in imbibed seeds, qualifying it as a high-throughput screening tool, which was further demonstrated by screening the seedlings of primary transformed T(0) seeds. Of the 30,000 germinating Arabidopsis seedlings screened, at least 69 GFP-positive lines were identified, accounting for an approximately 0.23% transformation efficiency. About 14,000 seedlings grown in 16 Petri plates could be screened within an hour, making the screening process significantly more efficient and robust than any other existing high-throughput screening method for transgenic plants.

Transcript profiles uncover temporal and stress-induced changes of metabolic pathways in germinating sugar beet seeds

BACKGROUND

With a cultivation area of 1.75 Mio ha and sugar yield of 16.7 Mio tons in 2006, sugar beet is a crop of great economic importance in Europe. The productivity of sugar beet is determined significantly by seed vigour and field emergence potential; however, little is known about the molecular mechanisms underlying these traits. Both traits exhibit large variations within sugar beet germplasm that have been difficult to ascribe to either environmental or genetic causes. Among potential targets for trait improvement, an enhancement of stress tolerance is considered because of the high negative influence of environmental stresses on trait parameters. Extending our knowledge of genetic and molecular determinants of sugar beet germination, stress response and adaptation mechanisms would facilitate the detection of new targets for breeding crop with an enhanced field emergence potential.

RESULTS

To gain insight into the sugar beet germination we initiated an analysis of gene expression in a well emerging sugar beet hybrid showing high germination potential under various environmental conditions. A total of 2,784 ESTs representing 2,251 'unigenes' was generated from dry mature and germinating seeds. Analysis of the temporal expression of these genes during germination under non-stress conditions uncovered drastic transcriptional changes accompanying a shift from quiescent to metabolically active stages of the plant life cycle. Assay of germination under stressful conditions revealed 157 genes showing significantly different expression patterns in response to stress. As deduced from transcriptome data, stress adaptation mechanisms included an alteration in reserve mobilization pathways, an accumulation of the osmoprotectant glycine betaine, late embryogenesis abundant proteins and detoxification enzymes. The observed transcriptional changes are supposed to be regulated by ABA-dependent signal transduction pathway.

CONCLUSION

This study provides an important step toward the understanding of main events and metabolic pathways during germination in sugar beet. The reported alterations of gene expression in response to stress shed light on sugar beet stress adaptation mechanisms. Some of the identified stress-responsive genes provide a new potential source for improvement of sugar beet stress tolerance during germination and field emergence.

ScORK17, a transmembrane receptor-like kinase predominantly expressed in ovules is involved in seed development

The mRNA expression of the Solanum chacoense Ovule Receptor Kinase 17 (ScORK17), a receptor kinase of the LRR-VI subfamily, is highly specific to the female reproductive tissues. No LRR-VI subfamily members in any plant species have yet been attributed a function. A phylogenetic tree inferred using the kinase domain of LRR-VI subfamily members separated the family into two clades: one containing an average of 8.2 LRR per protein and a second clade containing an average of 2.7. In situ hybridization analyses showed that the ScORK17 signal was mainly detected in the single ovule integument and in the endothelium. Transient expression analysis also revealed that ScORK17 was N-glycosylated in planta. Overexpression of ScORK17 in S. chacoense did not produce plants with an altered phenotype. However, when heterologous transformation was performed with a full-length ScORK17 clone in A. thaliana, the resulting transgenic plants showed reduced seed set, mainly due to aberrant embryo sac development, thus supporting a developmental role for ScORK17 in ovule and seed development.

Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

Water deficit arises as a result of low temperature, salinity and dehydration, thereby affecting plant growth adversely and making it imperative for plants to surmount such situations by acclimatizing/adapting at various levels. Water deficit stress results in significant changes in gene expression, mediated by interconnected signal transduction pathways that may be triggered by calcium, and regulated via ABA dependent and/or independent pathways. Hence, adaptation of plants to such stresses involves maintaining cellular homeostasis, detoxification of harmful elements and also growth alterations. Stress in general cause excess production of reactive oxygen species (ROS) and the plants overcome the same by either preventing the accumulation of ROS or by eliminating the ROS formed. Ion homeostasis includes processes such as cellular uptake, sequestration and export in conjunction with long distance transport. Requisite amounts of osmolytes are hence synthesized under stress to maintain turgor along with maintaining the macromolecular structures and also for scavenging ROS. Another noteworthy response is the accumulation of novel proteins, including enzymes involved in the biosynthesis of osmoprotectants, heat-shock proteins (HSPs), late embryogenesis abundant (LEA) proteins, antifreeze proteins, chaperones, detoxification enzymes, transcription factors, kinases and phosphatases. The LEAs belong to a redundant protein family and are highly hydrophilic, boiling-soluble, non-globular and therefore have been defined and classified accordingly. The precise function of LEAs is still unknown, but substantial evidence indicates their involvement in dessication tolerance as the expression of LEAs confers increased resistance to stress in heterologous yeast system and also significantly improves water deficit tolerance in transgenic plants. Genetic manipulation of plants towards conferring abiotic stress tolerance is a daunting task, as the abiotic stress tolerance mechanism is highly complex and various strategies have been exploited to address and evaluate the stress tolerance mechanism, and the molecular responses to water deficit via complex signaling networks. Genomic technologies have recently been useful in integrating the multigenicity of the plant stress responses through, transcriptomics, proteomics and metabolite profilling and their interactions. This review deals with the recent developments on genetic approaches for water stress tolerance in plants, with special emphasis on LEAs.

A transient assay system for the assessment of cell-autonomous gene function in dehydration-stressed barley

Drought is a serious, worldwide problem for crop production and also affects yields of barley and wheat, together with other stressors such as frost, viral diseases, or fungal pathogens. Although a number of candidate genes have been identified by transcriptome approaches in recent years, only very few have been tested in functional assays for a beneficial effect on drought tolerance. Here, a transient assay system in microprojectile-bombarded barley leaves is described that allows the functional testing of dehydration stress-related candidate genes by RNA interference (RNAi) or overexpression. Cellular stress or damage in dedydrated leaves is reported by a reduced accumulation of slowly maturing, native red-fluorescing protein DsRed that is known to be sensitive to denaturing conditions. After a dehydration-stress period of 4 d during which the relative fresh weight of leaves was kept at 60-66% of initial fresh weight, a reproducible reduction of normalized DsRed fluorescence was observed. In order to obtain proof of concept, a number of barley mRNAs homologous to drought response genes were selected and targeted by transient induced gene silencing (TIGS). TIGS of four tested genes resulted in a significantly stronger decrease of normalized DsRed fluorescence in dehydration-stressed leaves, whereas they had no effect in fully turgescent control leaves. These genes encode barley drought-responsive factor HvDRF1 (DREB2-like), dehydrin 6, late embryogenesis-abundant protein HVA1, and the vacuolar sodium/proton antiporter HvHNX1. The four targeted transcripts were also found to accumulate rapidly in dehydration-stressed barley leaf segments. The results suggest a value of the TIGS system for functional pre-screening of larger numbers of drought or dehydration stress-related candidate genes in barley.