Over-expression of (1,3;1,4)-β-D-glucanase isoenzyme EII gene results in decreased (1,3;1,4)-β-D-glucan content and increased starch level in barley grains

Cell- and development-specific degradation controls the levels of mixed-linkage glucan in sorghum leaves

Mixed-linkage glucan (MLG) is a component of the cell wall (CW) of grasses and is composed of glucose monomers linked by β-1,3 and β-1,4 bonds. MLG is believed to have several biological functions, such as the mobilizable storage of carbohydrates and structural support of the CW. The extracellular levels of MLG are largely controlled by rates of synthesis mediated by cellulose synthase-like (CSL) enzymes, and turnover by lichenases. Economically important crops like sorghum accumulate MLG to variable levels during development. While in sorghum, like other grasses, there is one major MLG synthase (CSLF6), the identity of lichenases is yet unknown. To fill this gap, we identified three sorghum lichenases (SbLCH1-3) and characterized them in leaves in relation to the expression of SbCSLF6, and the abundance of MLG and starch. We established that SbLCH1-3 are secreted to the apoplast, consistent with a role of degrading MLG extracellularly. Furthermore, while SbCSLF6 expression was associated with cell development, the SbLCH genes exhibited distinct development-, cell-type-specific and diel-regulated expression. Therefore, our study identifies three functional sorghum MLG lichenases and highlights that MLG accumulation in sorghum leaves is likely controlled by the activity of lichenases that tune MLG levels, possibly to suit distinct cell and developmental needs in planta. These findings have important implications for improving the growth, yield, and composition of sorghum as a feedstock.

Genetic engineering of complex feed enzymes into barley seed for direct utilization in animal feedstuff

Currently, feed enzymes are primarily obtained through fermentation of fungi, bacteria, and other microorganisms. Although the manufacturing technology for feed enzymes has evolved rapidly, the activities of these enzymes decline during the granulating process and the cost of application has increased over time. An alternative approach is the use of genetically modified plants containing complex feed enzymes for direct utilization in animal feedstuff. We co-expressed three commonly used feed enzymes (phytase, β-glucanase, and xylanase) in barley seeds using the Agrobacterium-mediated transformation method and generated a new barley germplasm. The results showed that these enzymes were stable and had no effect on the development of the seeds. Supplementation of the basal diet of laying hens with only 8% of enzyme-containing seeds decreased the quantities of indigestible carbohydrates, improved the availability of phosphorus, and reduced the impact of animal production on the environment to an extent similar to directly adding exogenous enzymes to the feed. Feeding enzyme-containing seeds to layers significantly increased the strength of the eggshell and the weight of the eggs by 10.0%-11.3% and 5.6%-7.7% respectively. The intestinal microbiota obtained from layers fed with enzyme-containing seeds was altered compared to controls and was dominated by Alispes and Rikenella. Therefore, the transgenic barley seeds produced in this study can be used as an ideal feedstuff for use in animal feed.

Advances in Cell Wall Matrix Research with a Focus on Mixed-Linkage Glucan

Mixed β(1,3;1,4)-linkage glucan (MLG) is commonly found in the monocot lineage, at particularly high levels in the Poaceae family, but also in the evolutionally distant genus, Equisetum. MLG has several properties that make it unique from other plant cell wall polysaccharides. It consists of β1,4-linked polymers of glucose interspersed with β1,3-linkages, but the presence of β1,3-linkages provides quite different physical properties compared to its closest form of the cell wall component, cellulose. The mechanisms of MLG biosynthesis have been investigated to understand whether single or multiple enzymes are required to build mixed linkages in the glucan chain. Currently, MLG synthesis by a single enzyme is supported by mutagenesis analyses of cellulose synthase-like F6, the major MLG synthase, but further investigation is needed to gather mechanistic insights. Because of transient accumulation of MLG in elongating cells and vegetative tissues, several hypotheses have been proposed to explain the role of MLG in the plant cell wall. Studies have been carried out to identify gene expression regulators during development and light cycles as well as enzymes involved in MLG organization in the cell wall. A role of MLG as a storage molecule in grains is evident, but the role of MLG in vegetative tissues is still not well understood. Characterization of a cell wall component is difficult due to the complex heterogeneity of the plant cell wall. However, as detailed in this review, recent exciting research has made significant impacts in the understanding of MLG biology in plants.

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.

Overexpression of HvHGGT Enhances Tocotrienol Levels and Antioxidant Activity in Barley

Vitamin E is a potent lipid-soluble antioxidant and essential nutrient for human health. Tocotrienols are the major form of vitamin E in seeds of most monocots. It has been known that homogentisate geranylgeranyl transferase (HGGT) catalyzes the committed step of tocotrienol biosynthesis. In the present study, we generated transgenic barley overexpressing HvHGGT under endogenous D-Hordein promoter (proHor). Overexpression of HvHGGT increased seed size and seed weight in transgenic barley. Notably, total tocotrienol content increased by 10-15% in seeds of transgenic lines, due to the increased levels of δ-, β-, and γ-tocotrienol, but not α-tocotrienol. Total tocopherol content decreased by 14-18% in transgenic lines, compared to wild type. The antioxidant activity of seeds was determined by using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), and lipid peroxidation assays. Compared to wild type, radical scavenging activity of seed extracts was enhanced by 17-18% in transgenic lines. Meanwhile, the lipid peroxidation level was decreased by about 20% in transgenic barley seeds. Taken together, overexpression of HvHGGT enhanced the tocotrienol levels and antioxidant capacity in barley seeds.

Comparative Analysis of γ-Oryzanol, β-Glucan, Total Phenolic Content and Antioxidant Activity in Fermented Rice Bran of Different Varieties

Rice bran, a by-product derived from processing rice, is a rich source of bioactive compounds. Recent studies have suggested that the fermentation can improve their biological activities. This study aimed to determined the level of γ-oryzanol, β-glucan and total phenol contents of fermented rice bran from 21 Korean varieties, as well as to evaluate their antioxidant activities. We also assessed the validation of the analytical method for determining γ-oryzanol content in fermented rice brans. Among the fermented rice brans, the Haedam rice bran contained the highest level of total phenol content (156.08 mg gallic acid equivalents/g), DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity (71.30%) and ORAC (Oxygen radical absorbance capacity) value (1101.31 μM trolox equivalents/g). Furthermore, the fermented Migwang rice bran showed the highest level of γ-oryzanol content (294.77 ± 6.74 mg/100 g).