The developmental program of seed formation, germination, and early seedling growth requires not only tight regulation of cell division and metabolism, but also concerted control of the structure and function of organelles, which relies on specific changes in their protein composition. Of particular interest is the switch from heterotrophic to photoautotrophic seedling growth, for which cytoplasmic lipid droplets (LDs) play a critical role as depots for energy-rich storage lipids. Here, we present the results of a bottom-up proteomics study analyzing the total protein fractions and LD-enriched fractions in eight different developmental phases during silique (seed) development, seed germination, and seedling establishment in Arabidopsis (Arabidopsis thaliana). The quantitative analysis of the LD proteome using LD-enrichment factors led to the identification of six previously unidentified and comparably low-abundance LD proteins, each of which was confirmed by intracellular localization studies with fluorescent protein fusions. In addition to these advances in LD protein discovery and the potential insights provided to as yet unexplored aspects in plant LD functions, our data set allowed for a comparative analysis of the LD protein composition throughout the various developmental phases examined. Among the most notable of the alterations in the LD proteome were those during seedling establishment, indicating a switch in the physiological function(s) of LDs after greening of the cotyledons. This work highlights LDs as dynamic organelles with functions beyond lipid storage.

中文翻译：

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种子和幼苗中低丰度脂滴蛋白的鉴定。

种子形成，发芽和幼苗早期生长的发育程序不仅需要严格调节细胞分裂和代谢，还需要对细胞器结构和功能的一致控制，这取决于其蛋白质组成的特定变化。特别引起关注的是从异养型向光养型幼苗生长的转变，为此，细胞质脂质小滴（LDs）作为富含能量的储存脂质的贮库发挥了关键作用。在这里，我们介绍了自下而上的蛋白质组学研究的结果，该研究分析了拟南芥（Arabidopsis thaliana）的角果（种子）发育，种子发芽和幼苗建立过程中八个不同发育阶段的总蛋白组分和LD富集组分。使用LD富集因子对LD蛋白质组进行定量分析，鉴定出了6种先前未鉴定且相对低丰度的LD蛋白，每种蛋白都通过荧光蛋白融合物的细胞内定位研究得到证实。除了这些在LD蛋白质发现方面的进展以及对植物LD功能尚未探索的方面提供的潜在见解之外，我们的数据集还允许在所研究的各个发育阶段对LD蛋白质组成进行比较分析。LD蛋白质组中最显着的变化是在幼苗建立过程中的变化，表明子叶变绿后LD的生理功能发生了变化。这项工作突出了LDs作为动态细胞器，其功能超出了脂质存储。