Neutral lipids in the form of triacylglycerol (TAG) have emerged as critical regulators of cellular energy balance, lipid homeostasis, growth, development and stress response in organisms ranging from plants to yeast. Although TAGs are mostly recognized as the main storage component in cytoplasmic lipid droplets (LDs), TAG-rich LDs with similar structural and functional characteristics to those found in the cytoplasm also exist in chloroplasts of microalgae and higher plants. Chloroplasts contain up to 70% of total lipids in photosynthetic cells, yet how organisms maintain chloroplast lipid homeostasis remains an under-investigated area of research. Here we summarize the current state of knowledge about the metabolism of TAG and its function in chloroplasts, with a focus on the enzymes catalyzing the final steps of TAG assembly and the role of TAG synthesis in protection against lipotoxicity. We also discuss emerging data regarding connections between cytoplasmic and chloroplast TAG metabolism and the role of autophagy in the degradation of chloroplast storage lipids.

以甘油三酯 (TAG) 形式存在的中性脂质已成为从植物到酵母等生物体的细胞能量平衡、脂质稳态、生长、发育和应激反应的关键调节剂。尽管 TAGs 大多被认为是细胞质脂滴 (LDs) 中的主要储存成分，但在微藻和高等植物的叶绿体中也存在与细胞质中发现的那些具有相似结构和功能特征的富含 TAG 的 LDs。叶绿体含有高达 70% 的光合细胞总脂质，但生物体如何维持叶绿体脂质稳态仍然是一个研究不足的研究领域。在这里，我们总结了关于 TAG 代谢及其在叶绿体中的功能的当前知识状态，重点关注催化 TAG 组装最后步骤的酶以及 TAG 合成在防止脂毒性方面的作用。我们还讨论了有关细胞质和叶绿体 TAG 代谢之间联系的新数据以及自噬在叶绿体储存脂质降解中的作用。