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Brachypodium distachyon: The New Cereal Model Plant for the Characterization and Biosynthesis of Starch

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandlingForskning

  • Vanja Tanackovic
Starch is one of the most abundant polysaccharides on the Earth, the principal energy storage of most plant species and of crucial significance for humans as a major nutrient in human diet. The majority of produced starch comes from cereals, domesticated grasses, characterized by specific en­hanced traits known as the domestication syndrome. Wild grasses, on the other side, still have traits lost during the process. Brachypodium distachyon (Brachypodium) is one of the wild grass recently introduced as a model plant for temperate cereals, closely related to pre-domesticated cereals such as barley (Hordeum vulgare). This thesis focuses on domestication of grasses – the cereal ancestors, starch in the grass Brachypodium distachyon, and its comparison to domesticated cereal. Grasses can potentially be used for the reintroduction of the lost grass traits, like health-promoting carbohydrates. Therefore, we compared grain starch metabolism in a wild grass, and in a cereal (Brachypodium and barley, respectively). Genes of Brachypodium starch metabolism were identified and annotated, including important motifs such as transit peptides and putative carbohydrate-binding modules (CBMs). Some of the interesting findings include markedly lower starch content in grains (12%) as compared to barley (47%); higher (1–3)(1–4)-β-glucan content (29% in Brachypodium compared to 4% in barley); and molecular disorder and low crystallinity of starch granules (10%) as compared to barley starch (20%). Brachypodium starch granules were bimodally distributed into distinct small B-type (2.5-10 μm) and very small C-type (0.5-2.5 μm), and had a shape characterised by concave disks with depressions in the centre. The expression profiles of most genes of starch biosynthesis in grain were distinctly different. Typ­ically, earlier decline over development is indicated in Brachypodium, which can explain the low starch content and differences in starch molecular structure and granule characteristics. Interestingly, high transitory starch in leaves of Brachypodium was observed after 14 h of light (2.8%), as compared to barley (1.9%). Brachypodium starch bioengineering was demonstrated by ge­netic transformation to provide transgenic Brachypodium lines expressing green fluorescent protein (GFP) driven by the barley hordein promoter. Additionally, this thesis aims to introduce the starch-recognising probe carbohydrate binding module family 20 (CBM20) from Aspergillus niger for detecting different starch structures using carbohydrate microarray high throughput screening. The screening method was validated using transgenic barley grain analysed over development and germination and Brachypodium starch.
OriginalsprogEngelsk
ForlagDepartment of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen
Antal sider173
StatusUdgivet - 2014

ID: 122555095