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

谷物发育的特点是组织的发育和退化所反映的巨大的结构和生理变化，以及大量储存化合物(淀粉、蛋白质和脂肪)的产生。这些发育过程已被证明与不同的代谢物分布模式相关。其中，不同类型果糖在籽粒组织中的积累具有时空规律性，指向发育阶段相关的功能。在贮藏前阶段，在大量淀粉生物合成开始之前，细胞化胚乳中合成了Levan和Graminan型低聚果聚糖。蔗糖转化为果糖被认为是为了保持较低的蔗糖水平，从而防止贮藏细胞的过早分化，直到胚乳细胞化完成。在贮藏期间，珠心突起(NP)合成菊粉型低聚果聚糖，并在胚乳传递细胞(ETC)和胚乳腔中积累。菊粉被认为是运输活性组织中的抗氧化剂，以保持胚乳的高同化物输入速率。该项目将解决并进一步研究谷物果聚糖代谢的假想作用。产生抑制特定果聚糖类型生物合成的转基因RNAi和CRISPR大麦品系将是监测与不同低聚果聚糖类型水平相关的籽粒发育变化的工具。通过击倒蔗糖：果聚糖6-果糖基转移酶(6-SFT)降低胚乳特定果聚糖(6-SFT)有望在储藏前阶段诱导较低的纤维素化，从而降低最终粒重。蔗糖：蔗糖1-果糖基转移酶(1-SST)的敲除抑制了转移组织中菊粉型果聚糖的积累，由于氧化胁迫的增加，预计会对同化物进入发育中的胚乳产生负面影响。限制养分进口将导致最终谷物重量和品质下降。遗传方法将与菊粉型果聚糖和果糖生物合成酶的亚细胞定位研究相辅相成。此外，人工膜的体外实验将被用来更详细地研究果聚糖作为抗氧化剂的作用。本研究的结果将有助于揭示低聚果聚糖在籽粒发育过程中的未知功能及其对最终籽粒品质的影响。此外，谷物果聚糖生理特性的描述将揭示整个糖调控网络的细节。

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.