Relevance of oligofructans for endosperm formation and filling during cereal grain development

• Applicant: Dr. Manuela Peukert
• Subject Area: Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: from 2015 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279623785

Cereal grain development is characterized by tremendous structural and physiological changes reflected by the development and degeneration of tissues and a massive production of storage compounds (starch, proteins and lipids). These developmental processes have been shown to correlate to distinct metabolite distribution patterns. Among them, a spatiotemporally regulated accumulation of various fructan types was revealed pointing towards developmental phase dependent functions in grain tissues. During the prestorage phase levan- and graminan-type oligofructans are synthesized in the cellularized endosperm just before the beginning of massive biosynthesis of starch. The conversion of sucrose into fructans is deemed to keep the sucrose level low and thus to prevent premature differentiation of storage cells until cellularization of the endosperm has finished. During the storage phase inulin-type oligofructans are synthesized in the nucellar projection (NP), and these fructans accumulate in endosperm transfer cells (ETC) and the endosperm cavity. The inulins are assumed to act as antioxidants in transport active tissues to maintain high rates of assimilate import into the endosperm. This project will address and further investigate the hypothesized roles of grain fructan metabolism. Generation of transgenic RNAi and CRISPR barley lines with suppressed biosynthesis of particular fructan types will be a tool to monitor alterations in grain development in respect to the level of the distinct oligofructan types. A reduction of endosperm specific fructans by knock-down of the sucrose:fructan 6-fructosyltransferase (6-SFT) is expected to induce a lowered cellularisation during the prestorage phase and consequently a reduced final grain weight. A suppressed accumulation of inulin-type fructans in transfer tissues by knock-out of the sucrose:sucrose 1-fructosyltransferase (1-SST) is expected to negatively affect the import of assimilates into the developing endosperm due to increased oxidative stress. Limitations in nutrient import will result in reduced final grain weight and quality. The genetic approach will be complemented with subcellular localization studies of inulin-type fructans and fructan biosynthesis enzymes. Furthermore, in vitro experiments with artificial membranes will be used to study the role of fructans as antioxidants in greater detail. The results of this study will contribute to unravelling the as yet unknown functions of oligofructans in grain developmental processes and their impact on final grain quality. Additionally, characterisation of grain fructan physiology will reveal details of overall sugar regulatory networks.

• DFG Programme: Research Fellowships
• International Connection: United Kingdom
• Host: Dr. Wendy Harwood