Subfamily Pooideae Research Articles

Intracellular position of mitochondria and chloroplasts in bundle sheath and mesophyll cells of C3 grasses in relation to photorespiratory CO2 loss

In C3 plants, photosynthetic efficiency is reduced by photorespiration. A part of CO2 fixed during photosynthesis in chloroplasts is lost from mitochondria during photorespiration by decarboxylation of glycine by glycine decarboxylase (GDC). Thus, the intracellular position of mitochondria in photosynthetic cells is critical to the rate of photorespiratory CO2 loss. We investigated the intracellular position of mitochondria in parenchyma sheath (PS) and mesophyll cells of 10 C3 grasses from 3 subfamilies (Ehrhartoideae, Panicoideae, and Pooideae) by immunostaining for GDC and light and electron microscopic observation. Immunostaining suggested that many mitochondria were located in the inner half of PS cells and on the vacuole side of chloroplasts in mesophyll cells. Organelle quantification showed that 62–75% of PS mitochondria were located in the inner half of cells, and 62–78% of PS chloroplasts were in the outer half. In mesophyll cells, 61–92% of mitochondria were positioned on the vacuole side of chloroplasts and stromules. In PS cells, such location would reduce the loss of photorespiratory CO2 by lengthening the path of CO2 diffusion and allow more efficient fixation of CO2 from intercellular spaces. In mesophyll cells, it would facilitate scavenging by chloroplasts of photorespiratory CO2 released from mitochondria. Our data suggest that the PS cells of C3 grasses have already acquired an initial structure leading to proto-Kranz and further C3–C4 intermediate anatomy. We also found that in the Pooideae, organelle positioning in PS cells on the phloem side resembles that in mesophyll cells.

Evidence for an Early Origin of Vernalization Responsiveness in Temperate Pooideae Grasses.

The ability of plants to match their reproductive output with favorable environmental conditions has major consequences both for lifetime fitness and geographic patterns of diversity. In temperate ecosystems, some plant species have evolved the ability to use winter nonfreezing cold (vernalization) as a cue to ready them for spring flowering. However, it is unknown how important the evolution of vernalization responsiveness has been for the colonization and subsequent diversification of taxa within the northern and southern temperate zones. Grasses of subfamily Pooideae, including several important crops, such as wheat (Triticum aestivum), barley (Hordeum vulgare), and oats (Avena sativa), predominate in the northern temperate zone, and it is hypothesized that their radiation was facilitated by the early evolution of vernalization responsiveness. Predictions of this early origin hypothesis are that a response to vernalization is widespread within the subfamily and that the genetic basis of this trait is conserved. To test these predictions, we determined and reconstructed vernalization responsiveness across Pooideae and compared expression of wheat vernalization gene orthologs VERNALIZATION1 (VRN1) and VRN3 in phylogenetically representative taxa under cold and control conditions. Our results demonstrate that vernalization responsive Pooideae species are widespread, suggesting that this trait evolved early in the lineage and that at least part of the vernalization gene network is conserved throughout the subfamily. These results are consistent with the hypothesis that the evolution of vernalization responsiveness was important for the initial transition of Pooideae out of the tropics and into the temperate zone.

Phylogenetic relationships of the ‘Briza complex’ to other members of the subfamily Pooideae (Poaceae)

Background and aims - The species of the 'Briza complex' (Pooideae, Poaceae) are distributed in South America and Eurasia. They are relatively well-studied morphologically and have a complex taxono ...

Is plant evolutionary history impacting recruitment of diazotrophs and nifH expression in the rhizosphere?

Plant evolutionary history influences the taxonomic composition of the root-associated bacterial community, but whether it can also modulate its functioning is unknown. Here, we tested the hypothesis that crop diversification is a significant factor determining the ecology of the functional group of nitrogen-fixing bacteria the rhizosphere of Poaceae. A greenhouse experiment was carried out using a range of Poaceae, i.e. four Zea mays varieties (from two genetic groups) and teosinte (representing maize’s ancestor), sorghum (from the same Panicoideae subfamily), and wheat (from neighboring Pooideae subfamily), as well as the dicot tomato as external reference. Diazotroph rhizosphere community was characterized at 21 days in terms of size (quantitative PCR of nifH genes), composition (T-RFLP and partial sequencing of nifH alleles) and functioning (quantitative RT-PCR, T-RFLP and partial sequencing of nifH transcripts). Plant species and varieties had a significant effect on diazotroph community size and the number of nifH transcripts per root system. Contrarily to expectations, however, there was no relation between Poaceae evolutionary history and the size, diversity or expression of the rhizosphere diazotroph community. These results suggest a constant selection of this functional group through evolution for optimization of nitrogen fixation in the rhizosphere.

Alpine grassland palaeoecology of the Virunga Volcanoes, East Africa: A new phytolith record from Mt. Muhavura

Abstract This study presents a first attempt at using phytoliths from a high-altitude crater lake as a palaeoecological tool at a tropical montane site. Mt. Muhavura (4127 m asl) at the border of Uganda and Rwanda is part of the Virunga volcanoes located in the Albertine Rift, one of the most biodiverse areas in Africa. To investigate the potential of phytoliths to record grassland history in an Afroalpine environment, a unique and little studied ecosystem, we analysed the phytolith content of 37 sediment samples from a 159 cm sediment core from the crater lake at the summit of Mt. Muhavura representing the last ca. 2400 years BP. Ten plant species from the Alpine belt were also analysed for their main phytolith morphotypes. Phytoliths from the sediments were grouped into 12 main categories and the most frequently occurring individual morphotypes were bilobate (33%), oblong (16%), elongate (17%) and globular psilate (13%). The phytolith assemblage consists predominantly of phytoliths characteristic of grasses (70%). A literal interpretation of the results would be that Panicoideae grasses (mainly C 4 ) that are characteristic of warm and wet climate and C 3 Pooideae subfamily grasses characteristic of cold climate/high altitude have co-existed throughout the late Holocene in this belt. As only C 3 cold climate grass subfamilies are known to occur at this altitude today, the abundance of short cell phytoliths (bilobates) typical of Panicoideae grasses in the lake sediments at this altitude presents a new perspective to the phytolith discussion. The C 3 Pooideae grasses analysed did not produce bilobates. In this study, the phytolith index, Ic that is used as a proxy of past grass subfamily dominance is not representative of the taxonomic significance for which it is known. This study suggests that caution needs to be taken when using bilobate morphotypes and the Ic as indicators of grass subfamily dominance at high altitude on East African mountains as the bilobates may not be taxonomically representative of the grasses for which they are typically known. This highlights the inherent problem of phytolith redundancy even at an altitude where C 3 /C 4 grass distribution is better delineated.

The shape factors of phytoliths in selected plants from the Changbai Mountains and their implications

Phytoliths as a climate proxy are one of the most important and effective tools for reconstruction of paleoenvironment. In this paper, twelve Gramineae species of the subfamilies Panicoideae, Pooideae and Arundinoideae from the Changbai Mountains were selected, and 3698 phytoliths were counted. We measured six parameters of dumbell, elongate, lanceolate, crenate, saddle and silicified stomata. The seven shape factors of different types of phytoliths were deduced by the six parameters measured above and analyzed by nonparametric testing and discriminant analysis.The nonparametric testing indicated that the average value of the shape factor SF4 among the three subfamilies was obviously different. Discriminant analysis for the three subfamilies, also revealed that the discriminant accuracy was high (89.81%). Total discriminant accuracy using shape factors of dumbell phytoliths of Panicoideae was 73.12%. Discriminant accuracies using shape factors of elongate, lanceolate and crenate phytoliths of Pooideae were respectively 60.87, 59.21 and 87.07%. The discriminant accuracies using shape factors of saddle phytoliths and silicified stomata of Arundinoideae were 59.06 and 71.77%. At the same time, the shape factors of phytoliths from Setaria viridis and Leymus chinensis were used to test whether the discriminant functions established at the subfamily level were effective or not. Results showed discriminant functions precisely classify them, thus verified discriminant functions were useful. In conclusion, using the seven shape factors of phytoliths not only may improve the accuracy of classifying Gramineae, but also provides basis reference data for better understanding the presence and function of Gramineae plants at archaeological sites.

A synteny-based draft genome sequence of the forage grass Lolium perenne.

Here we report the draft genome sequence of perennial ryegrass (Lolium perenne), an economically important forage and turf grass species that is widely cultivated in temperate regions worldwide. It is classified along with wheat, barley, oats and Brachypodium distachyon in the Pooideae sub-family of the grass family (Poaceae). Transcriptome data was used to identify 28,455 gene models, and we utilized macro-co-linearity between perennial ryegrass and barley, and synteny within the grass family, to establish a synteny-based linear gene order. The gametophytic self-incompatibility mechanism enables the pistil of a plant to reject self-pollen and therefore promote out-crossing. We have used the sequence assembly to characterize transcriptional changes in the stigma during pollination with both compatible and incompatible pollen. Characterization of the pollen transcriptome identified homologs to pollen allergens from a range of species, many of which were expressed to very high levels in mature pollen grains, and are potentially involved in the self-incompatibility mechanism. The genome sequence provides a valuable resource for future breeding efforts based on genomic prediction, and will accelerate the development of new varieties for more productive grasslands.

TaFROG Encodes a Pooideae Orphan Protein That Interacts with SnRK1 and Enhances Resistance to the Mycotoxigenic Fungus Fusarium graminearum.

All genomes encode taxonomically restricted orphan genes, and the vast majority are of unknown function. There is growing evidence that such genes play an important role in the environmental adaptation of taxa. We report the functional characterization of an orphan gene (Triticum aestivum Fusarium Resistance Orphan Gene [TaFROG]) as a component of resistance to the globally important wheat (T. aestivum) disease, Fusarium head blight. TaFROG is taxonomically restricted to the grass subfamily Pooideae. Gene expression studies showed that it is a component of the early wheat response to the mycotoxin deoxynivalenol (DON), which is a virulence factor produced by the causal fungal agent of Fusarium head blight, Fusarium graminearum. The temporal induction of TaFROG by F. graminearum in wheat spikelets correlated with the activation of the defense Triticum aestivum Pathogenesis-Related-1 (TaPR1) gene. But unlike TaPR1, TaFROG induction by F. graminearum was toxin dependent, as determined via comparative analysis of the effects of wild-type fungus and a DON minus mutant derivative. Using virus-induced gene silencing and overexpressing transgenic wheat lines, we present evidence that TaFROG contributes to host resistance to both DON and F. graminearum. TaFROG is an intrinsically disordered protein, and it localized to the nucleus. A wheat alpha subunit of the Sucrose Non-Fermenting1-Related Kinase1 was identified as a TaFROG-interacting protein based on a yeast two-hybrid study. In planta bimolecular fluorescence complementation assays confirmed the interaction. Thus, we conclude that TaFROG encodes a new Sucrose Non-Fermenting1-Related Kinase1-interacting protein and enhances biotic stress resistance.

Determination of growth stages and metabolic profiles in Brachypodium distachyon for comparison of developmental context with Triticeae crops.

Brachypodium distachyon is an emerging model plant for studying biological phenomena in temperate grasses. Study of the growth scale is essential to analyse spatio-temporal changes in molecular factors throughout the life cycle. For sensitive and robust staging based on morphology in B. distachyon, we demonstrated the utility of the BBCH (Biologische Bundesanstalt, Bundessortenamt and CHemical industry) scale, which is comparable to the Zadoks scale conventionally used for Triticeae crops. We compared the chronological progression of B. distachyon accessions Bd21 and Bd3-1, in addition to the progression of Chinese Spring wheat. The comparison of growth stages illustrates the morphological similarities and differences in the timing of life cycle events. Furthermore, we compared metabolite accumulation patterns across different growth stages and across different stress conditions using a widely targeted metabolome analysis. Metabolic profiling determined commonalities and specificities in chemical properties that were dependent on organisms, growth stages and/or stress conditions. Most metabolites accumulated equivalently in B. distachyon and wheat. This qualitative similarity indicated the superiority of B. distachyon as a model for Triticeae crops. The growth scale of B. distachyon should provide a conceptual framework for comparative analysis and for knowledge integration between this model grass and crops in the Pooideae subfamily.

Comparative transcriptome analysis within the Lolium/Festuca species complex reveals high sequence conservation.

BackgroundThe Lolium-Festuca complex incorporates species from the Lolium genera and the broad leaf fescues, both belonging to the subfamily Pooideae. This subfamily also includes wheat, barley, oat and rye, making it extremely important to world agriculture. Species within the Lolium-Festuca complex show very diverse phenotypes, and many of them are related to agronomically important traits. Analysis of sequenced transcriptomes of these non-model species may shed light on the molecular mechanisms underlying this phenotypic diversity.ResultsWe have generated de novo transcriptome assemblies for four species from the Lolium-Festuca complex, ranging from 52,166 to 72,133 transcripts per assembly. We have also predicted a set of proteins and validated it with a high-confidence protein database from three closely related species (H. vulgare, B. distachyon and O. sativa). We have obtained gene family clusters for the four species using OrthoMCL and analyzed their inferred phylogenetic relationships. Our results indicate that VRN2 is a candidate gene for differentiating vernalization and non-vernalization types in the Lolium-Festuca complex. Grouping of the gene families based on their BLAST identity enabled us to divide ortholog groups into those that are very conserved and those that are more evolutionarily relaxed. The ratio of the non-synonumous to synonymous substitutions enabled us to pinpoint protein sequences evolving in response to positive selection. These proteins may explain some of the differences between the more stress tolerant Festuca, and the less stress tolerant Lolium species.ConclusionsOur data presents a comprehensive transcriptome sequence comparison between species from the Lolium-Festuca complex, with the identification of potential candidate genes underlying some important phenotypical differences within the complex (such as VRN2). The orthologous genes between the species have a very high %id (91,61%) and the majority of gene families were shared for all of them. It is likely that the knowledge of the genomes will be largely transferable between species within the complex.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1447-y) contains supplementary material, which is available to authorized users.

A multi-locus analysis of phylogenetic relationships within grass subfamily Pooideae (Poaceae) inferred from sequences of nuclear single copy gene regions compared with plastid DNA

To investigate phylogenetic relationships within the grass subfamily Pooideae we studied about 50 taxa covering all recognized tribes, using one plastid DNA (cpDNA) marker (matK gene–3′trnK exon) and for the first time four nuclear single copy gene loci. DNA sequence information from two parts of the nuclear genes topoisomerase 6 (Topo6) spanning the exons 8–13 and 17–19, the exons 9–13 encoding plastid acetyl-CoA-carboxylase (Acc1) and the partial exon 1 of phytochrome B (PhyB) were generated. Individual and nuclear combined data were evaluated using maximum parsimony, maximum likelihood and Bayesian methods. All of the phylogenetic results show Brachyelytrum and the tribe Nardeae as earliest diverging lineages within the subfamily. The ‘core’ Pooideae (Hordeeae and the Aveneae/Poeae tribe complex) are also strongly supported, as well as the monophyly of the tribes Brachypodieae, Meliceae and Stipeae (except PhyB). The beak grass tribe Diarrheneae and the tribe Duthieeae are not monophyletic in some of the analyses. However, the combined nuclear DNA (nDNA) tree yields the highest resolution and the best delimitation of the tribes, and provides the following evolutionary hypothesis for the tribes: Brachyelytrum, Nardeae, Duthieeae, Meliceae, Stipeae, Diarrheneae, Brachypodieae and the ‘core’ Pooideae. Within the individual datasets, the phylogenetic trees obtained from Topo6 exon 8–13 shows the most interesting results. The divergent positions of some clone sequences of Ampelodesmos mauritanicus and Trikeraia pappiformis, for instance, may indicate a hybrid origin of these stipoid taxa.

Karyosystematics of the Australasian stipoid grass Austrostipa and related genera: chromosome sizes, ploidy, chromosome base numbers and phylogeny

Mitotic metaphase chromosomes were counted in 29 taxa, representing 11 subgenera of Austrostipa, and in 11 species from nine related genera of the grass subfamily Pooideae. Karyotype features were also measured. The cytogenetic data were mapped on molecular phylogenetic trees based on nuclear ITS and plastid 3ʹtrnK DNA sequence data. The trees showed four different main lineages within Austrostipa, but supported only two of the 13 acknowledged subgenera. The phylogenetic positions of the genera Anemanthele, Achnatherum, Nassella and Oloptum indicated paraphyly of the genus Austrostipa. In nuclear-sequence data, Anemanthele was nested within Austrostipa; however, in plastid-sequence data, both were sisters. The newly obtained chromosome counts in Austrostipa showed that most species have 2n = 44, the other 2n = 66. Presuming a chromosome base number of x = 11, the counts corresponded with ploidy levels of 4x and 6x respectively. Karyotype data of Austrostipa and Anemanthele were very similar. Chromosome counting in further genera suggested chromosome base numbers of x = 9, 10, 11, 12 and 13. Chromosome sizes of the phylogenetically derived tribe Stipeae were smaller than those of the earliest diverging Pooideae lineages Nardeae, Meliceae and Phaenospermateae. The mechanisms of chromosome evolution and the origin of the considerable variation in chromosome base numbers in the subfamily Pooideae are discussed in the context of chromosome evolution and biosystematics.

Design of plant-specific PCR primers for the ETS region with enhanced specificity for tribeBromeaeand their application to other grasses (Poaceae)

Selective primers were developed for the amplification via polymerase chain reaction (PCR) of the external transcribed spacer (ETS) region in the nuclear ribosomal repeat unit. These primers were intended to be specific to the Poaceae tribe Bromeae but were found to function broadly across subfamily Pooideae. ETS primers previously developed for grasses were unable to amplify tribe Bromeae taxa because of ETS variability and several subrepeats. After detailed analysis, a region was chosen and four candidate primers were designed to amplify and sequence the ETS fragment. This fragment of approximately 800–900 bp is located in the 3′ region of the ETS of 18S–26S nuclear ribosomal DNA. A preliminary study with these primers was conducted in eight samples of Bromus. The best two primers showed strong amplification and successful sequencing for all samples tested. We also tested the specificity of these two primers in samples belonging to all large taxa of Bromeae, including all three genera and five subgenera and samples of eight tribes and 15 subtribes of the subfamily Pooideae, and both worked for most of the taxa tested. Our results demonstrate that the ETS region is more informative for resolving relationships at different taxonomic levels than internal transcribed spacer region. Also, these results indicate the utility of these new primers for studying the ETS region in the tribe Bromeae as well as across the subfamily Pooideae.

The role of seasonal flowering responses in adaptation of grasses to temperate climates.

Grasses of the subfamily Pooideae, including important cereal crops and pasture grasses, are widespread in temperate zones. Seasonal regulation of developmental transitions coordinates the life cycles of Pooideae with the passing seasons so that flowering and seed production coincide with favorable conditions in spring. This review examines the molecular pathways that control the seasonal flowering responses of Pooideae and how variation in the activity of genes controlling these pathways can adapt cereals or grasses to different climates and geographical regions. The possible evolutionary origins of the seasonal flowering responses of the Pooideae are discussed and key questions for future research highlighted. These include the need to develop a better understanding of the molecular basis for seasonal flowering in perennial Pooideae and in temperate grasses outside the core Pooideae group.

Anther ontogeny in Brachypodium distachyon.

Brachypodium distachyon has emerged as a model plant for the improvement of grain crops such as wheat, barley and oats and for understanding basic biological processes to facilitate the development of grasses as superior energy crops. Brachypodium is also the first species of the grass subfamily Pooideae with a sequenced genome. For obtaining a better understanding of the mechanisms controlling male gametophyte development in B. distachyon, here we report the cellular changes during the stages of anther development, with special reference to the development of the anther wall. Brachypodium anthers are tetrasporangiate and follow the typical monocotyledonous-type anther wall formation pattern. Anther differentiation starts with the appearance of archesporial cells, which divide to generate primary parietal and primary sporogenous cells. The primary parietal cells form two secondary parietal layers. Later, the outer secondary parietal layer directly develops into the endothecium and the inner secondary parietal layer forms an outer middle layer and inner tapetum by periclinal division. The anther wall comprises an epidermis, endothecium, middle layer and the secretory-type tapetum. Major documented events of anther development include the degradation of a secretory-type tapetum and middle layer during the course of development and the rapid formation of U-shaped endothecial thickenings in the mature pollen grain stage. The tapetum undergoes degeneration at the tetrad stage and disintegrates completely at the bicellular stage of pollen development. The distribution of insoluble polysaccharides in the anther layers and connective tissue through progressive developmental stages suggests their role in the development of male gametophytes. Until sporogenous cell stage, the amount of insoluble polysaccharides in the anther wall was negligible. However, abundant levels of insoluble polysaccharides were observed during microspore mother cell and tetrad stages and gradually declined during the free microspore and vacuolated microspore stages to undetectable level at the mature stage. Thus, the cellular features in the development of anthers in B. distachyon share similarities with anther and pollen development of other members of Poaceae.

Assessment of genetic diversity among cereals and millets based on PCR amplification using Dof (DNA binding with One Finger) transcription factor gene-specific primers

The genetic diversity among cereals and millets were assessed based on PCR amplification pattern derived from 4 Dof domain and 20 Dof genes specific primers. Multiple bands showing variability in terms of both number and sizes of bands ranging from 0.1 to 3.0 kbp were observed. Out of a total of 906 bands, 894 polymorphic and 12 monomorphic bands were obtained and the percentage of polymorphism ranged from 69.23 to 100 %. A very high degree of polymorphism was observed with all the primers except Dof-24 primer and the genetic diversity ranged from 0.0601 to 0.2118 among these crops. The Jaccard’s similarity matrices based dendrogram obtained using UPGMA method revealed two major clusters designated as A and B. The major cluster A comprises of rice, sorghum, maize, finger millet, foxtail millet, barnyard millet and proso millet representing Oryzoideae, Panicoideae, Chloridoideae subfamilies while cluster B with wheat, barley, oat, little millet and kodo millet represents predominantly pooideae subfamily. These major clusters were further bifurcated into two sub-clusters each having members representing almost the same subfamilies.

VibA, a homologue of a transcription factor for fungal heterokaryon incompatibility, is involved in antifungal compound production in the plant-symbiotic fungus Epichloë festucae.

Symbiotic association of epichloae endophytes (Epichloë/Neotyphodium species) with cool-season grasses of the subfamily Pooideae confers bioprotective benefits to the host plants against abiotic and biotic stresses. While the production of fungal bioprotective metabolites is a well-studied mechanism of host protection from insect herbivory, little is known about the antibiosis mechanism against grass pathogens by the mutualistic endophyte. In this study, an Epichloë festucae mutant defective in antimicrobial substance production was isolated by a mutagenesis approach. In an isolated mutant that had lost antifungal activity, the exogenous DNA fragment was integrated into the promoter region of the vibA gene, encoding a homologue of the transcription factor VIB-1. VIB-1 in Neurospora crassa is a regulator of genes essential in vegetative incompatibility and promotion of cell death. Here we show that deletion of the vibA gene severely affected the antifungal activity of the mutant against the test pathogen Drechslera erythrospila. Further analyses showed that overexpressing vibA enhanced the antifungal activity of the wild-type isolate against test pathogens. Transformants overexpressing vibA showed an inhibitory activity on test pathogens that the wild-type isolate could not. Moreover, overexpressing vibA in a nonantifungal E. festucae wild-type Fl1 isolate enabled the transformant to inhibit the mycelial and spore germination of D. erythrospila. These results demonstrate that enhanced expression of vibA is sufficient for a nonantifungal isolate to obtain antifungal activity, implicating the critical role of VibA in antifungal compound production by epichloae endophytes.

Grass pollen allergens globally: the contribution of subtropical grasses to burden of allergic respiratory diseases

Grass pollens of the temperate (Pooideae) subfamily and subtropical subfamilies of grasses are major aeroallergen sources worldwide. The subtropical Chloridoideae (e.g. Cynodon dactylon; Bermuda grass) and Panicoideae (e.g. Paspalum notatum; Bahia grass) species are abundant in parts of Africa, India, Asia, Australia and the Americas, where a large and increasing proportion of the world's population abide. These grasses are phylogenetically and ecologically distinct from temperate grasses. With the advent of global warming, it is conceivable that the geographic distribution of subtropical grasses and the contribution of their pollen to the burden of allergic rhinitis and asthma will increase. This review aims to provide a comprehensive synthesis of the current global knowledge of (i) regional variation in allergic sensitivity to subtropical grass pollens, (ii) molecular allergenic components of subtropical grass pollens and (iii) allergic responses to subtropical grass pollen allergens in relevant populations. Patients from subtropical regions of the world show higher allergic sensitivity to grass pollens of Chloridoideae and Panicoideae grasses, than to temperate grass pollens. The group 1 allergens are amongst the allergen components of subtropical grass pollens, but the group 5 allergens, by which temperate grass pollen extracts are standardized for allergen content, appear to be absent from both subfamilies of subtropical grasses. Whilst there are shared allergenic components and antigenic determinants, there are additional clinically relevant subfamily-specific differences, at T- and B-cell levels, between pollen allergens of subtropical and temperate grasses. Differential immune recognition of subtropical grass pollens is likely to impact upon the efficacy of allergen immunotherapy of patients who are primarily sensitized to subtropical grass pollens. The literature reviewed herein highlights the clinical need to standardize allergen preparations for both types of subtropical grass pollens to achieve optimal diagnosis and treatment of patients with allergic respiratory disease in subtropical regions of the world.

Arabidopsis galactinol synthase AtGolS2 improves drought tolerance in the monocot model Brachypodium distachyon

Brachypodium distachyon (purple false brome) is a herbaceous species belonging to the grass subfamily Pooideae, which also includes major crops like wheat, barley, oat and rye. The species has been established as experimental model organism for understanding and improving cereal crops and temperate grasses. The complete genome of Bd21, the community standard line of B. distachyon, has been sequenced and protocols for Agrobacterium-mediated transformation have been published. Further improvements to the experimental platform including better evaluation systems for transgenic plants are still needed. Here we describe the growth conditions for Bd21 plants yielding highly responsive immature embryos that can generate embryogenic calli for transformation. A prolonged 20-h photoperiod produced seeds with superior immature embryos. In addition, osmotic treatment of embryogenic calli enhanced the efficiency of transfection by particle bombardment. We generated transgenic plants expressing Arabidopsis thaliana galactinol synthase 2 (AtGolS2) in these experiments. AtGolS2-expressing transgenics displayed significantly improved drought tolerance, increasing with increased expression of AtGolS2. These results demonstrate that AtGolS2 can confer drought tolerance to monocots and confirm that Brachypodium is a useful model to further explore ways to understand and improve major monocot crop species.

An isolate of Epichloë festucae, an endophytic fungus of temperate grasses, has growth inhibitory activity against selected grass pathogens

The symbiotic association of epichloae endophytes (Epichloe/Neotyphodium species) with temperate grasses of the subfamily Pooideae is known to enhance plant host tolerance to abiotic and biotic stresses. While the protection of the host plant from insect herbivory by epichloae endophytes is well characterized, the mechanism by which they protect their host against grass pathogens is largely unknown. Here, we assessed a geographically diverse collection of 14 Epichloe festucae isolates for in vitro antifungal activity against 8 grass pathogens. Isolate E437 of E. festucae, which had the broadest antifungal spectrum, inhibited growth of Drechslera erythrospila, D. siccans, D. dictyoides, Colletotrichum graminicola and Bipolaris sorokiniana. As shown with confocal microscopy, the endophyte reduced hyphal tip growth and differentiation of the pathogen, but did not cause any lysis. The isolate produced a thermostable, low-molecular-weight antifungal compound in culture. Disease symptoms caused by D. erythrospila on perennial ryegrass plants infected with E437 were reduced, suggesting the antifungal compound produced by E. festucae E437 isolate could be involved in the protection of the host plant.