Yazaki Euki, Uehara Tadaaki, Sakamoto Hirokazu, Inagaki Yuji
Research Center for Advanced Analysis, National Agriculture and Food Research Organization, Tsukuba, Ibaraki, Japan; RIKEN iTHEMS, Wako, Saitama, Japan.
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Protist. 2024 Dec;175(6):126067. doi: 10.1016/j.protis.2024.126067. Epub 2024 Sep 21.
Autophagy is an intracellular degradation mechanism by which cytoplasmic materials are delivered to and degraded in the lysosome-fused autophagosome (autolysosome) and proposed to have been established at an early stage of eukaryotic evolution. Dinoflagellates harboring endosymbiotic diatoms (so-called "dinotoms"), which retain their own nuclei and mitochondria in addition to plastids, have been investigated as an intermediate toward the full integration of a eukaryotic phototroph into the host-controlled organelle (i.e., plastid) through endosymbiosis. Pioneering studies systematically evaluated the degree of host governance on several metabolic pathways in the endosymbiotic diatoms (ESDs). However, little attention has been paid to the impact of the endosymbiotic lifestyle on the autophagy operated in the ESDs. In this study, we searched for ATG3, ATG4, ATG5, ATG7, ATG8, ATG10, and ATG12, which are required for autophagosome formation, in the RNA-seq data from dinotoms Durinskia baltica and Kryptoperidinium foliaceum. We detected two evolutionally distinct sets of the ATG proteins in the dinotom species, one affiliated with the dinoflagellate homologs and the other with the diatom homologs in phylogenetic analyses. The results suggest that the ATG proteins descended from the diatom taken up by the dinoflagellate host persist for autophagosome formation and, most likely, autophagy.
自噬是一种细胞内降解机制，通过该机制细胞质物质被输送到与溶酶体融合的自噬体（自噬溶酶体）中并在其中降解，且被认为是在真核生物进化的早期阶段就已确立。含有内共生硅藻的甲藻（所谓的“甲藻硅藻复合体”），除了质体外还保留自己的细胞核和线粒体，已被作为真核光合生物通过内共生完全整合到宿主控制的细胞器（即质体）过程中的一个中间阶段进行研究。开创性研究系统地评估了宿主对几种内共生硅藻（ESD）代谢途径的控制程度。然而，内共生生活方式对ESD中自噬的影响却很少受到关注。在本研究中，我们在甲藻硅藻复合体波罗的海杜氏藻和叶状隐甲藻的RNA测序数据中搜索了自噬体形成所需的ATG3、ATG4、ATG5、ATG7、ATG8、ATG10和ATG12。在系统发育分析中，我们在甲藻硅藻复合体物种中检测到两组进化上不同的ATG蛋白，一组与甲藻同源物相关，另一组与硅藻同源物相关。结果表明，由甲藻宿主摄取的硅藻来源的ATG蛋白持续参与自噬体形成，并且很可能参与自噬。
