Zhang Yanhua, Zhang Xiaochen, Cui Huanshuo, Ma Xinzhu, Hu Guipeng, Wei Jing, He Yikun, Hu Yong
College of Life Science, Capital Normal University, Beijing, China.
Front Plant Sci. 2021 Nov 22;12:752790. doi: 10.3389/fpls.2021.752790. eCollection 2021.
Chloroplasts evolved from a free-living cyanobacterium through endosymbiosis. Similar to bacterial cell division, chloroplasts replicate by binary fission, which is controlled by the Minicell (Min) system through confining FtsZ ring formation at the mid-chloroplast division site. MinD, one of the most important members of the Min system, regulates the placement of the division site in plants and works cooperatively with MinE, ARC3, and MCD1. The loss of MinD function results in the asymmetric division of chloroplasts. In this study, we isolated one large dumbbell-shaped and asymmetric division chloroplast Arabidopsis mutant Chloroplast Division Mutant 75 () that contains a missense mutation, changing the arginine at residue 49 to a histidine (R49H), and this mutant point is located in the N-terminal Conserved Terrestrial Sequence (NCTS) motif of AtMinD1, which is only typically found in terrestrial plants. This study provides sufficient evidence to prove that residues 1-49 of AtMinD1 are transferred into the chloroplast, and that the R49H mutation does not affect the function of the AtMinD1 chloroplast transit peptide. Subsequently, we showed that the point mutation of R49H could remove the punctate structure caused by residues 1-62 of the AtMinD1 sequence in the chloroplast, suggesting that the arginine in residue 49 (Arg49) is essential for localizing the punctate structure of AtMinD1 on the chloroplast envelope. Unexpectedly, we found that AtMinD1 could interact directly with ARC6, and that the R49H mutation could prevent not only the previously observed interaction between AtMinD1 and MCD1 but also the interaction between AtMinD1 and ARC6. Thus, we believe that these results show that the AtMinD1 NCTS motif is required for their protein interaction. Collectively, our results show that AtMinD1 can guide the placement of the division site to the mid chloroplast through its direct interaction with ARC6 and reveal the important role of AtMinD1 in regulating the AtMinD1-ARC6 interaction.
叶绿体通过内共生从一种自由生活的蓝细菌进化而来。与细菌细胞分裂类似，叶绿体通过二分裂进行复制，这由微细胞（Min）系统控制，通过将FtsZ环的形成限制在叶绿体分裂位点的中部。MinD是Min系统最重要的成员之一，它调节植物中分裂位点的位置，并与MinE、ARC3和MCD1协同工作。MinD功能的丧失导致叶绿体的不对称分裂。在本研究中，我们分离出了一个大哑铃形且不对称分裂的叶绿体拟南芥突变体叶绿体分裂突变体75（），该突变体包含一个错义突变，将第49位的精氨酸变为组氨酸（R49H），且该突变位点位于AtMinD1的N端保守陆地序列（NCTS）基序中，该基序仅在陆地植物中典型存在。本研究提供了充分的证据证明AtMinD1的第1 - 49位残基被转运到叶绿体中，并且R49H突变不影响AtMinD1叶绿体转运肽的功能。随后，我们表明R49H点突变可以消除叶绿体中由AtMinD1序列的第1 - 62位残基引起的点状结构，这表明第49位残基中的精氨酸（Arg49）对于将AtMinD1的点状结构定位在叶绿体被膜上至关重要。出乎意料的是，我们发现AtMinD1可以直接与ARC6相互作用，并且R49H突变不仅可以阻止先前观察到的AtMinD1与MCD1之间的相互作用，还可以阻止AtMinD1与ARC6之间的相互作用。因此，我们认为这些结果表明AtMinD1的NCTS基序对于它们的蛋白质相互作用是必需的。总的来说，我们的结果表明AtMinD1可以通过其与ARC6的直接相互作用将分裂位点引导到叶绿体中部，并揭示了AtMinD1在调节AtMinD1 - ARC6相互作用中的重要作用。
