Department of Plant Physiology and Biotechnology, University of Gdańsk, Wita Stwosza 59, Gdańsk 80-308, Poland.
Department for Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, University of Goettingen, Justus-von-Liebig-Weg 11, Goettingen 37077, Germany.
Plant Physiol. 2023 Nov 22;193(4):2361-2380. doi: 10.1093/plphys/kiad471.
Lipid droplets (LDs) of seed tissues are storage organelles for triacylglycerols (TAGs) that provide the energy and carbon for seedling establishment. In the major route of LD degradation (lipolysis), TAGs are mobilized by lipases. However, LDs may also be degraded via lipophagy, a type of selective autophagy, which mediates LD delivery to vacuoles or lysosomes. The exact mechanisms of LD degradation and the mobilization of their content in plants remain unresolved. Here, we provide evidence that LDs are degraded via a process morphologically resembling microlipophagy in Arabidopsis (Arabidopsis thaliana) seedlings. We observed the entry and presence of LDs in the central vacuole as well as their breakdown. Moreover, we show co-localization of AUTOPHAGY-RELATED PROTEIN 8b (ATG8b) and LDs during seed germination and localization of lipidated ATG8 (ATG8-PE) to the LD fraction. We further demonstrate that structural LD proteins from the caleosin family, CALEOSIN 1 (CLO1), CALEOSIN 2 (CLO2), and CALEOSIN 3 (CLO3), interact with ATG8 proteins and possess putative ATG8-interacting motifs (AIMs). Deletion of the AIM localized directly before the proline knot disrupts the interaction of CLO1 with ATG8b, suggesting a possible role of this region in the interaction between these proteins. Collectively, we provide insights into LD degradation by microlipophagy in germinating seeds with a particular focus on the role of structural LD proteins in this process.
种子组织中的脂滴 (LDs) 是三酰基甘油 (TAGs) 的储存细胞器，可为幼苗的建立提供能量和碳。在 LD 降解的主要途径（脂解）中，TAGs 被脂肪酶动员。然而，LD 也可能通过脂噬作用降解，这是一种选择性自噬，介导 LD 递送至液泡或溶酶体。LD 降解的精确机制及其在植物中内容物的动员仍未解决。在这里，我们提供的证据表明，在拟南芥（Arabidopsis thaliana）幼苗中，LD 通过形态上类似于微噬脂作用的过程降解。我们观察到 LD 进入并存在于中央液泡中，以及它们的分解。此外，我们显示在种子萌发过程中 ATG8b 和 LD 的共定位以及脂化 ATG8（ATG8-PE）在 LD 部分的定位。我们进一步证明，钙调蛋白家族的结构 LD 蛋白，钙调蛋白 1（CLO1）、钙调蛋白 2（CLO2）和钙调蛋白 3（CLO3），与 ATG8 蛋白相互作用并具有潜在的 ATG8 相互作用基序 (AIM)。直接在脯氨酸结之前定位的 AIM 缺失破坏了 CLO1 与 ATG8b 的相互作用，这表明该区域可能在这些蛋白之间的相互作用中发挥作用。总的来说，我们深入了解了萌发种子中通过微噬脂作用进行的 LD 降解，特别关注结构 LD 蛋白在这个过程中的作用。
