A comparative view of grain development in Brachypodium distachyon

Microautophagy in cereal grains: protein storage or degradation?

Recent research indicates an involvement of microautophagy in the uptake of seed storage proteins (SSPs) into the plant-specific protein storage vacuole (PSV), particularly in cereal grains. However, because microautophagy plays a vital role in cellular homeostasis by degrading and recycling cellular components, we question whether it is a suitable term for a process involved in long-term storage. Additionally, because fission-type microautophagy shares mechanistic similarities with the intraluminal vesicle (ILV) formation of multivesicular bodies (MVBs), we draw parallels between microautophagy and membrane remodeling facilitated by the endosomal sorting complex required for transport (ESCRT). Finally, we propose that the complex structure of cereal endosperm is an optimal tissue to study microautophagy in a plant- and tissue-specific context to decipher its molecular regulation in anabolism and catabolism.

Mixed-Linkage Glucan Is the Main Carbohydrate Source and Starch Is an Alternative Source during Brachypodium Grain Germination

Seeds of the model grass Brachypodium distachyon are unusual because they contain very little starch and high levels of mixed-linkage glucan (MLG) accumulated in thick cell walls. It was suggested that MLG might supplement starch as a storage carbohydrate and may be mobilised during germination. In this work, we observed massive degradation of MLG during germination in both endosperm and nucellar epidermis. The enzymes responsible for the MLG degradation were identified in germinated grains and characterized using heterologous expression. By using mutants targeting MLG biosynthesis genes, we showed that the expression level of genes coding for MLG and starch-degrading enzymes was modified in the germinated grains of knocked-out cslf6 mutants depleted in MLG but with higher starch content. Our results suggest a substrate-dependent regulation of the storage sugars during germination. These overall results demonstrated the function of MLG as the main carbohydrate source during germination of Brachypodium grain. More astonishingly, cslf6 Brachypodium mutants are able to adapt their metabolism to the lack of MLG by modifying the energy source for germination and the expression of genes dedicated for its use.

The molecular basis of zinc homeostasis in cereals

Plants require zinc (Zn) as an essential cofactor for diverse molecular, cellular and physiological functions. Zn is crucial for crop yield, but is one of the most limiting micronutrients in soils. Grasses like rice, wheat, maize and barley are crucial sources of food and nutrients for humans. Zn deficiency in these species therefore not only reduces annual yield but also directly results in Zn malnutrition of more than two billion people in the world. There has been good progress in understanding Zn homeostasis and Zn deficiency mechanisms in plants. However, our current knowledge of monocots, including grasses, remains insufficient. In this review, we provide a summary of our knowledge of molecular Zn homeostasis mechanisms in monocots, with a focus on important cereal crops. We additionally highlight divergences in Zn homeostasis of monocots and the dicot model Arabidopsis thaliana, as well as important gaps in our knowledge that need to be addressed in future research on Zn homeostasis in cereal monocots.

Comparative Analysis of Coding and Non-Coding Features within Insect Tolerance Loci in Wheat with Their Homologs in Cereal Genomes

Food insecurity and malnutrition have reached critical levels with increased human population, climate fluctuations, water shortage; therefore, higher-yielding crops are in the spotlight of numerous studies. Abiotic factors affect the yield of staple food crops; among all, wheat stem sawfly (Cephus cinctus Norton) and orange wheat blossom midge (Sitodiplosis mosellana) are two of the most economically and agronomically harmful insect pests which cause yield loss in cereals, especially in wheat in North America. There is no effective strategy for suppressing this pest damage yet, and only the plants with intrinsic tolerance mechanisms such as solid stem phenotypes for WSS and antixenosis and/or antibiosis mechanisms for OWBM can limit damage. A major QTL and a causal gene for WSS resistance were previously identified in wheat, and 3 major QTLs and a causal gene for OWBM resistance. Here, we present a comparative analysis of coding and non-coding features of these loci of wheat across important cereal crops, barley, rye, oat, and rice. This research paves the way for our cloning and editing of additional WSS and OWBM tolerance gene(s), proteins, and metabolites.

Programmed Cell Death in Developing Brachypodium distachyon Grain

The normal developmental sequence in a grass grain entails the death of several maternal and filial tissues in a genetically regulated process termed programmed cell death (PCD). The progression and molecular aspects of PCD in developing grains have been reported for domesticated species such as barley, rice, maize and wheat. Here, we report a detailed investigation of PCD in the developing grain of the wild model species Brachypodium distachyon. We detected PCD in developing Brachypodium grains using molecular and histological approaches. We also identified in Brachypodium the orthologs of protease genes known to contribute to grain PCD and surveyed their expression. We found that, similar to cereals, PCD in the Brachypodium nucellus occurs in a centrifugal pattern following anthesis. However, compared to cereals, the rate of post-mortem clearance in the Brachypodium nucellus is slower. However, compared to wheat and barley, mesocarp PCD in Brachypodium proceeds more rapidly in lateral cells. Remarkably, Brachypodium mesocarp PCD is not coordinated with endosperm development. Phylogenetic analysis suggests that barley and wheat possess more vacuolar processing enzymes that drive nucellar PCD compared to Brachypodium and rice. Our expression analysis highlighted putative grain-specific PCD proteases in Brachypodium. Combined with existing knowledge on grain PCD, our study suggests that the rate of nucellar PCD moderates grain size and that the pattern of mesocarp PCD influences grain shape.

Allotetraploidization in Brachypodium May Have Led to the Dominance of One Parent's Metabolome in Germinating Seeds

Seed germination is a complex process during which a mature seed resumes metabolic activity to prepare for seedling growth. In this study, we performed a comparative metabolomic analysis of the embryo and endosperm using the community standard lines of three annual Brachypodium species, i.e., B. distachyon (Bd) and B. stacei (Bs) and their natural allotetraploid B. hybridum (BdBs) that has wider ecological range than the other two species. We explored how far the metabolomic impact of allotetraploidization would be observable as over-lapping changes at 4, 12, and 24 h after imbibition (HAI) with water when germination was initiated. Metabolic changes during germination were more prominent in Brachypodium embryos than in the endosperm. The embryo and endosperm metabolomes of Bs and BdBs were similar, and those of Bd were distinctive. The Bs and BdBs embryos showed increased levels of sugars and the tricarboxylic acid cycle compared to Bd, which could have been indicative of better nutrient mobilization from the endosperm. Bs and BdBs also showed higher oxalate levels that could aid nutrient transfer through altered cellular events. In Brachypodium endosperm, the thick cell wall, in addition to starch, has been suggested to be a source of nutrients to the embryo. Metabolites indicative of sugar metabolism in the endosperm of all three species were not prominent, suggesting that mobilization mostly occurred prior to 4 HAI. Hydroxycinnamic and monolignol changes in Bs and BdBs were consistent with cell wall remodeling that arose following the release of nutrients to the respective embryos. Amino acid changes in both the embryo and endosperm were broadly consistent across the species. Taking our data together, the formation of BdBs may have maintained much of the Bs metabolome in both the embryo and endosperm during the early stages of germination. In the embryo, this conserved Bs metabolome appeared to include an elevated sugar metabolism that played a vital role in germination. If these observations are confirmed in the future with more Brachypodium accessions, it would substantiate the dominance of the Bs metabolome in BdBs allotetraploidization and the use of metabolomics to suggest important adaptive changes.

Characterisation of Cellulose Synthase Like F6 (CslF6) Mutants Shows Altered Carbon Metabolism in β-D-(1,3;1,4)-Glucan Deficient Grain in Brachypodium distachyon

Brachypodium distachyon is a small, fast growing grass species in the Pooideae subfamily that has become established as a model for other temperate cereals of agricultural significance, such as barley (Hordeum vulgare) and wheat (Triticum aestivum). The unusually high content in whole grains of β-D-(1,3;1,4)-glucan or mixed linkage glucan (MLG), considered a valuable dietary fibre due to its increased solubility in water compared with cellulose, makes B. distachyon an attractive model for these polysaccharides. The carbohydrate composition of grain in B. distachyon is interesting not only in understanding the synthesis of MLG, but more broadly in the mechanism(s) of carbon partitioning in cereal grains. Several mutants in the major MLG synthase, cellulose synthase like (CSL) F6, were identified in a screen of a TILLING population that show a loss of function in vitro. Surprisingly, loss of cslf6 synthase capacity appears to have a severe impact on survival, growth, and development in B. distachyon in contrast to equivalent mutants in barley and rice. One mutant, A656T, which showed milder growth impacts in heterozygotes shows a 21% (w/w) reduction in average grain MLG and more than doubling of starch compared with wildtype. The endosperm architecture of grains with the A656T mutation is altered, with a reduction in wall thickness and increased deposition of starch in larger granules than typical of wildtype B. distachyon. Together these changes demonstrate an alteration in the carbon storage of cslf6 mutant grains in response to reduced MLG synthase capacity and a possible cross-regulation with starch synthesis which should be a focus in future work in composition of these grains. The consequences of these findings for the use of B. distachyon as a model species for understanding MLG synthesis, and more broadly the implications for improving the nutritional value of cereal grains through alteration of soluble dietary fibre content are discussed.

Biochemical and physiological flexibility accompanies reduced cellulose biosynthesis in Brachypodium cesa1 S830N

Here, we present a study into the mechanisms of primary cell wall cellulose formation in grasses, using the model cereal grass Brachypodium distachyon. The exon found adjacent to the BdCESA1 glycosyltransferase QXXRW motif was targeted using Targeting Induced Local Lesions in Genomes (TILLING) and sequencing candidate amplicons in multiple parallel reactions (SCAMPRing) leading to the identification of the Bdcesa1 ^S830N allele. Plants carrying this missense mutation exhibited a significant reduction in crystalline cellulose content in tissues that rely on the primary cell wall for biomechanical support. However, Bdcesa1 ^S830N plants failed to exhibit the predicted reduction in plant height. In a mechanism unavailable to eudicotyledons, B. distachyon plants homozygous for the Bdcesa1 ^S830N allele appear to overcome the loss of internode expansion anatomically by increasing the number of nodes along the stem. Stem biomechanics were resultantly compromised in Bdcesa1 ^S830N . The Bdcesa1 ^S830N missense mutation did not interfere with BdCESA1 gene expression. However, molecular dynamic simulations of the CELLULOSE SYNTHASE A (CESA) structure with modelled membrane interactions illustrated that Bdcesa1 ^S830N exhibited structural changes in the translated gene product responsible for reduced cellulose biosynthesis. Molecular dynamic simulations showed that substituting S830N resulted in a stabilizing shift in the flexibility of the class specific region arm of the core catalytic domain of CESA, revealing the importance of this motion to protein function.

Spatial and temporal distribution of cell wall polysaccharides during grain development of Brachypodium distachyon

Brachypodium distachyon (Brachypodium) is now well considered as being a suitable plant model for studying temperate cereal crops. Its cell walls are phylogenetically intermediate between rice and poaceae, with a greater proximity to these latter. By microscopic and biochemical approaches, this work gives an overview of the temporal and spatial distribution of cell wall polysaccharides in the grain of Brachypodium from the end of the cellularization step to the maturation of grain. Variation in arabinoxylan chemical structure and distribution were demonstrated according to development and different grain tissues. In particular, the kinetic of arabinoxylan feruloylation was shown occuring later in the aleurone layers compared to storage endosperm. Mixed linked β-glucan was detected in whole the tissues of Brachypodium grain even at late stage of development. Cellulose was found in both the storage endosperm and the outer layers. Homogalacturonan and rhamnogalacturonan I epitopes were differentially distributed within the grain tissues. LM5 galactan epitope was restricted to the aleurone layers contrary to LM6 arabinan epitope which was detected in the whole endosperm. A massive deposition of highly methylated homogalacturonans in vesicular bodies was observed underneath the cell wall of the testa t2 layer at early stage of development. At maturity, low-methylated homogalacturonans totally fulfilled the lumen of the t2 cell layer, suggesting pectin remodeling during grain development. Xyloglucans were only detected in the cuticle above the testa early in the development of the grain while feruloylated arabinoxylans were preferentially deposited into the cell wall of t1 layer. Indeed, the circumscribed distribution of some of the cell wall polysaccharides raises questions about their role in grain development and physiology.

In Brachypodium a complex signaling is actuated to protect cells from proteotoxic stress and facilitate seed filling

A conserved UPR machinery is required for Brachypodium ER stress resistance and grain filling. Human and livestock diets depend on the accumulation of cereal storage proteins and carbohydrates, including mixed-linkage glucan (MLG), in the endosperm during seed development. Storage proteins and proteins responsible for the production of carbohydrates are synthesized in the endoplasmic reticulum (ER). Unfavorable conditions during growth that hamper the ER biosynthetic capacity, such as heat, can cause a potentially lethal condition known as ER stress, which activates the unfolded protein response (UPR), a signaling response designed to mitigate ER stress. The UPR relies primarily on a conserved ER-associated kinase and ribonuclease, IRE1, which splices the mRNA of a transcription factor (TF), such as bZIP60 in plants, to produce an active TF that controls the expression of ER resident chaperones. Here, we investigated activation of the UPR in Brachypodium, as a model to study the UPR in seeds of a monocotyledon species, as well as the consequences of heat stress on MLG deposition in seeds. We identified a Brachypodium bZIP60 orthologue and determined a positive correlation between bZIP60 splicing and ER stress induced by chemicals and heat. Each stress condition led to transcriptional modulation of several BiP genes, supporting the existence of condition-specific BiP regulation. Finally, we found that the UPR is elevated at the early stage of seed development and that MLG production is negatively affected by heat stress via modulation of MLG synthase accumulation. We propose that successful accomplishment of seed filling is strongly correlated with the ability of the plant to sustain ER stress via the UPR.

Identification of candidate genes for the seed coat colour change in a Brachypodium distachyon mutant induced by gamma radiation using whole-genome re-sequencing

Brachypodium distachyon has been proposed as a model plant for agriculturally important cereal crops such as wheat and barley. Seed coat colour change from brown-red to yellow was observed in a mutant line (142-3) of B. distachyon, which was induced by chronic gamma radiation. In addition, dwarf phenotypes were observed in each of the lines 142-3, 421-2, and 1376-1. To identify causal mutations for the seed coat colour change, the three mutant lines and the wild type were subjected to whole-genome re-sequencing. After removing natural variations, 906, 1057, and 978 DNA polymorphisms were detected in 142-3, 421-2, and 1376-1, respectively. A total of 13 high-risk DNA polymorphisms were identified in mutant 142-3. Based on a comparison with DNA polymorphisms in 421-2 and 1376-1, candidate causal mutations for the seed coat colour change in 142-3 were selected. In the two independent Arabidopsis thaliana lines carrying T-DNA insertions in the AtCHI, seed colour change was observed. We propose a frameshift mutation in BdCHI1 as a causal mutation responsible for seed colour change in 142-3. The DNA polymorphism information for these mutant lines can be utilized for functional genomics in B. distachyon and cereal crops.

Characterization of globulin storage proteins of a low prolamin cereal species in relation to celiac disease

Brachypodium distachyon, a small annual grass with seed storage globulins as primary protein reserves was used in our study to analyse the toxic nature of non-prolamin seed storage proteins related to celiac disease. The main storage proteins of B. distachyon are the 7S globulin type proteins and the 11S, 12S seed storage globulins similar to oat and rice. Immunoblot analyses using serum samples from celiac disease patients were carried out followed by the identification of immune-responsive proteins using mass spectrometry. Serum samples from celiac patients on a gluten-free diet, from patients with Crohn’s disease and healthy subjects, were used as controls. The identified proteins with intense serum-IgA reactivity belong to the 7S and 11–12S seed globulin family. Structure prediction and epitope predictions analyses confirmed the presence of celiac disease-related linear B cell epitope homologs and the presence of peptide regions with strong HLA-DQ8 and DQ2 binding capabilities. These results highlight that both MHC-II presentation and B cell response may be developed not only to prolamins but also to seed storage globulins. This is the first study of the non-prolamin type seed storage proteins of Brachypodium from the aspect of the celiac disease.

Molecular characterization and evolutionary origins of farinin genes in Brachypodium distachyon L

Farinins are one of the oldest members of the gluten family in wheat and Aegilops species, and they influence dough properties. Here, we performed the first detailed molecular genetic study on farinin genes in Brachypodium distachyon L., the model species for Triticum aestivum. A total of 51 b-type farinin genes were cloned and characterized, including 27 functional and 24 non-functional pseudogenes from 14 different B. distachyon accessions. All genes were highly similar to those previously reported from wheat and Aegilops species. The identification of deduced amino acid sequences showed that b-type farinins across Triticeae genomes could be classified as b1-, b2-, b3-, and b4-type farinins; however, B. distachyon had only b3- and b4-type farinins. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) revealed that farinin genes are transcribed into mRNA in B. distachyon at much lower levels than in Triticeae, despite the presence of cis-acting elements in promoter regions. Phylogenetic analysis suggested that Brachypodium farinins may have closer relationships with common wheat and further confirmed four different types of b-type farinins in Triticeae and Brachypodium genomes, corresponding to b1, b2, b3 (group 1), and b4 (group 2). A putative evolutionary origin model of farinin genes in Brachypodium, Triticum, and the related species suggests that all b-type farinins diverged from their common ancestor ~3.2 million years ago (MYA). The b3 and b4 types could be considered older in the farinin family. The results explain the loss of b1- and b2-type farinin alleles in Brachypodium.

The deposition and characterization of starch in Brachypodium distachyon

Brachypodium distachyon is a non-domesticated cereal. Nonetheless, Brachypodium was recently introduced as a model plant for temperate cereals. This study compares grain starch metabolism in Brachypodium and barley (Hordeum vulgare). In Brachypodium, we identified and annotated 28 genes involved in starch metabolism and identified important motifs including transit peptides and putative carbohydrate-binding modules (CBMs) of the families CBM20, CBM45, CBM48, and CBM53. Starch content was markedly lower in Brachypodium grains (12%) compared to barley grains (47%). Brachypodium starch granules were doughnut shaped and bimodally distributed into distinct small B-type (2.5-10 µm) and very small C-type (0.5-2.5 µm) granules. Large A-type granules, typical of cereals, were absent. Starch-bound phosphate, important for starch degradation, was 2-fold lower in Brachypodium compared with barley indicating different requirements for starch mobilization. The amylopectin branch profiles were similar and the amylose content was only slightly higher compared with barley cv. Golden Promise. The crystallinity of Brachypodium starch granules was low (10%) compared to barley (20%) as determined by wide-angle X-ray scattering (WAXS) and molecular disorder was confirmed by differential scanning calorimetry (DSC). The expression profiles in grain for most genes were distinctly different for Brachypodium compared to barley, typically showing earlier decline during the course of development, which can explain the low starch content and differences in starch molecular structure and granule characteristics. High transitory starch levels were observed in leaves of Brachypodium (2.8% after 14h of light) compared to barley (1.9% after 14h of light). The data suggest important pre-domesticated features of cereals.

The fruit, the whole fruit, and everything about the fruit

Fruits come in an impressive array of shapes, sizes, and consistencies, and also display a huge diversity in biochemical/metabolite profiles, wherein lies their value as rich sources of food, nutrition, and pharmaceuticals. This is in addition to their fundamental function in supporting and dispersing the developing and mature seeds for the next generation. Understanding developmental processes such as fruit development and ripening, particularly at the genetic level, was once largely restricted to model and crop systems for practical and commercial reasons, but with the expansion of developmental genetic and evo-devo tools/analyses we can now investigate and compare aspects of fruit development in species spanning the angiosperms. We can superimpose recent genetic discoveries onto the detailed characterization of fruit development and ripening conducted with primary considerations such as yield and harvesting efficiency in mind, as well as on the detailed description of taxonomically relevant characters. Based on our own experience we focus on two very morphologically distinct and evolutionary distant fruits: the capsule of opium poppy, and the grain or caryopsis of cereals. Both are of massive economic value, but because of very different constituents; alkaloids of varied pharmaceutical value derived from secondary metabolism in opium poppy capsules, and calorific energy fuel derived from primary metabolism in cereal grains. Through comparative analyses in these and other fruit types, interesting patterns of regulatory gene function diversification and conservation are beginning to emerge.

Evolution and development of cell walls in cereal grains

The composition of cell walls in cereal grains and other grass species differs markedly from walls in seeds of other plants. In the maternal tissues that surround the embryo and endosperm of the grain, walls contain higher levels of cellulose and in many cases are heavily lignified. This may be contrasted with walls of the endosperm, where the amount of cellulose is relatively low, and the walls are generally not lignified. The low cellulose and lignin contents are possible because the walls of the endosperm perform no load-bearing function in the mature grain and indeed the low levels of these relatively intractable wall components are necessary because they allow rapid degradation of the walls following germination of the grain. The major non-cellulosic components of endosperm walls are usually heteroxylans and (1,3;1,4)-β-glucans, with lower levels of xyloglucans, glucomannans, and pectic polysaccharides. Pectic polysaccharides and xyloglucans are the major non-cellulosic wall constituents in most dicot species, in which (1,3;1,4)-β-glucans are usually absent and heteroxylans are found at relatively low levels. Thus, the "core" non-cellulosic wall polysaccharides in grain of the cereals and other grasses are the heteroxylans and, more specifically, arabinoxylans. The (1,3;1,4)-β-glucans appear in the endosperm of some grass species but are essentially absent from others; they may constitute from zero to more than 45% of the cell walls of the endosperm, depending on the species. It is clear that in some cases these (1,3;1,4)-β-glucans function as a major store of metabolizable glucose in the grain. Cereal grains and their constituent cell wall polysaccharides are centrally important as a source of dietary fiber in human societies and breeders have started to select for high levels of non-cellulosic wall polysaccharides in grain. To meet end-user requirements, it is important that we understand cell wall biology in the grain both during development and following germination.

The wheat HMW-glutenin 1Dy10 gene promoter controls endosperm expression in Brachypodium distachyon

The grass species Brachypodium distachyon has emerged as a model system for the study of gene structure and function in temperate cereals. As a first demonstration of the utility of Brachypodium to study wheat gene promoter function, we transformed it with a T-DNA that included the uidA reporter gene under control of a wheat High-Molecular-Weight Glutenin Subunit (HMW-GS) gene promoter and transcription terminator. For comparison, the same expression cassette was introduced into wheat by biolistics. Histochemical staining for β-glucuronidase (GUS) activity showed that the wheat promoter was highly expressed in the endosperms of all the seeds of Brachypodium and wheat homozygous plants. It was not active in any other tissue of transgenic wheat, but showed variable and sporadic activity in a minority of styles of the pistils of four homozygous transgenic Brachypodium lines. The ease of obtaining transgenic Brachypodium plants and the overall faithfulness of expression of the wheat HMW-GS promoter in those plants make it likely that this model system can be used for studies of other promoters from cereal crop species that are difficult to transform.

Molecular characterisation and evolution of HMW glutenin subunit genes in Brachypodium distachyon L

Brachypodium distachyon, a small wild grass within the Pooideae family, is a new model organism for exploring the functional genomics of cereal crops. It was shown to have close relationships to wheat, barley and rice. Here, we describe the molecular characterisation and evolutionary relationships of high molecular weight glutenin subunits (HMW-GS) genes from B. distachyon. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), high performance capillary electrophoresis (HPCE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses demonstrated that there was no HMW-GS expression in the Brachypodium grains due to the silencing of their encoding genes. Through allele-specific polymerase chain reaction (AS-PCR) amplification and cloning, a total of 13 HMW-GS encoding genes from diploid, tetraploid and hexaploid Brachypodium species were obtained, and all of them had typical structural features of y-type HMW-GS genes from common wheat and related species, particularly more similar to the 1Dy12 gene. However, the presence of an in-frame premature stop codon (TAG) at position 1521 in the coding region resulted in the conversion of all the genes to pseudogenes. Further, quantitative real-time PCR (qRT-PCR) analysis revealed that HMW-GS genes in B. distachyon displayed a similar trend, but with a low transcriptional expression profile during grain development due to the occurrence of the stop codon. Phylogenetic analysis showed that the highly conserved Glu-1-2 loci were presented in B. distachyon, which displayed close phylogenetic evolutionary relationships with Triticum and related species.

Grain development in Brachypodium and other grasses: possible interactions between cell expansion, starch deposition, and cell-wall synthesis

To explain the low levels of starch, high levels of (1,3;1,4)-β-glucan, and thick cell walls in grains of Brachypodium distachyon L. relative to those in other Pooideae, aspects of grain development were compared between B. distachyon and barley (Hordeum vulgare L.). Cell proliferation, cell expansion, and endoreduplication were reduced in B. distachyon relative to barley and, consistent with these changes, transcriptional downregulation of the cell-cycle genes CDKB1 and cyclin A3 was observed. Similarly, reduced transcription of starch synthase I and starch-branching enzyme I was observed as well as reduced activity of starch synthase and ADP-glucose pyrophosphorylase, which are consistent with the lowered starch content in B. distachyon grains. No change was detected in transcription of the major gene involved in (1,3;1,4)-β-glucan synthesis, cellulose synthase-like F6. These results suggest that, while low starch content results from a reduced capacity for starch synthesis, the unusually thick cell walls in B. distachyon endosperm probably result from continuing (1,3;1,4)-β-glucan deposition in endosperm cells that fail to expand. This raises the possibility that endosperm expansion is linked to starch deposition.

Brachypodium distachyon as a model for defining the allergen potential of non-prolamin proteins

Epitope databases and the protein sequences of published plant genomes are suitable to identify some of the proteins causing food allergies and sensitivities. Brachypodium distachyon, a diploid wild grass with a sequenced genome and low prolamin content, is the closest relative of the allergen cereals, such as wheat or barley. Using the Brachypodium genome sequence, a workflow has been developed to identify potentially harmful proteins which may cause either celiac disease or wheat allergy-related symptoms. Seed tissue-specific expression of the potential allergens has been determined, and intact epitopes following an in silico digestion with several endopeptidases have been identified. Molecular function of allergen proteins has been evaluated using Gene Ontology terms. Biologically overrepresented proteins and potentially allergen protein families have been identified.