Inositol as a regulator of seedling development

环糖醇肌醇在植物的多种代谢途径中起着核心作用。肌醇可以通过从头生物合成从葡萄糖中获得，但也可以通过肌醇转运蛋白进入细胞或从液泡中释放。细胞内肌醇含量的变化，例如在生物合成突变体中，导致多效效应，如含肌醇的膜组分水平的改变，膜动力学的影响和幼苗发育的缺陷。此外，生长素信号通过改变生长素外排载体的膜定位而受损。拟南芥有三种转运蛋白用于将肌醇运送到细胞质中：质膜中的AtINT2和AtINT4以及细胞质中的AtINT1。如果将肌醇从液泡转运到细胞质的AtINT1蛋白缺失，这些AtINT1幼苗的根和黄化下胚轴的细胞伸长受到抑制。只有在培养基中加入蔗糖时才会发生这种情况。与野生型相比，在无蔗糖培养基上生长的Atint1植株没有表现出明显的生长差异，但含有肌醇的膜成分水平增加。Atint1幼苗与肌醇生物合成缺陷突变植株的比较表明，表型差异并不依赖于肌醇缺乏，而是细胞内肌醇分布不平衡。本项目旨在揭示细胞内肌醇运输所维持的肌醇平衡对植物发育的影响。由于肌醇参与了许多不同的过程，我们将采用不同的方法来处理肌醇运输改变的多效效应。分析的代谢物的收集将被扩展，例如，在植物中具有信号功能的磷酸化肌醇将被包括在内。它将被分析，如果蔗糖起到营养或信号分子的作用。由于肌醇参与多种代谢途径，对肌醇代谢关键酶编码基因的表达分析将揭示Atint1突变体与野生型相比，哪些代谢途径发生了变化。在Atint1幼苗中定位生长素外溢载体，并使用生长素反应标记来可视化植物中生长素的分布，将阐明缺失的肌醇运输和生长素信号传导之间的潜在联系。此外，研究将进一步关注Atint1植物与野生型的表型差异，例如向地性，其中肌醇的贡献已经被描述。

The cyclic sugar alcohol inositol plays a central role in various metabolic pathways in plants. Inositol can be derived from glucose via de novo-biosynthesis, but also be imported into the cell or released from the vacuole via inositol transport proteins. Changes in intracellular inositol content, e.g. in biosynthesis mutants, lead to pleiotropic effects such as altered levels of inositol-containing membrane components, affected membrane dynamics and defects in seedling development. Moreover, auxin signalling is impaired by changing the membrane localisation of auxin efflux carriers.Arabidopsis thaliana has three transport proteins for the import of inositol into the cytosol: AtINT2 and AtINT4 in the plasma membrane and AtINT1 in the tonoplast. If the AtINT1 protein, which transports inositol out of the vacuole into the cytoplasm, is missing, these Atint1 seedlings show an inhibition of cell elongation in roots and in etiolated hypocotyls. This only occurs when sucrose is added to the growth medium. Atint1 plants grown on medium without sucrose do not show apparent growth differences compared to wild type, but have increased levels of inositol-containing membrane components. Comparison of Atint1 seedlings with mutant plants defective in inositol biosynthesis revealed that the observed phenotypic differences do not rely on inositol deficiency, but rather on imbalance in intracellular inositol distribution.The aim of this project is to unravel the impact of inositol balance maintained by intracellular inositol transport on plant development. Because inositol is involved in many different processes we will perform various approaches to cope with the pleiotropic effects of altered inositol transport. The collection of metabolites analysed will be extended, e.g. phosphorylated inositols with supposed signalling function in plants will be included.It will be analysed, if sucrose plays a role as nutrimental or signalling molecule.Due to the fact that inositol is involved in various metabolic pathways, expression analysis of genes encoding key enzymes in inositol metabolism will reveal which metabolic pathways are changed in the Atint1 mutant compared to wild type.Localisation of auxin effluc carriers in Atint1 seedlings and use of an auxin response marker that visualises auxin distribution in plants will elucidate a potential connection between missing inositol transport and auxin signalling. Additionally, research will focus on further phenotypic differences of Atint1 plants compared to wild type, e.g. gravitropism, for which a contribution of inositol was already described.