Abstract
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 (cdm75) 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 AtMinD11–62 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.
Highlights
Chloroplasts, photosynthetic organelles in plants, evolved from an ancestral cyanobacterium harboring their own genomes and internal membrane systems related to the components of modern cyanobacteria (Gray, 1999)
We obtained a mutant with abnormal chloroplast division named Chloroplast-Divisionrelated Mutant 75, that was found to have a typical ethyl methane sulfonate (EMS)-induced point mutation
Expression pattern is one of the key factors needed to recover a phenotype (Fujiwara et al, 2004). These findings showed that cdm75 was a loss-of-function mutant of AtMinD1, and that the observed phenotype was caused by a single residue 49 to a histidine (R49H) mutant
Summary
Chloroplasts, photosynthetic organelles in plants, evolved from an ancestral cyanobacterium harboring their own genomes and internal membrane systems related to the components of modern cyanobacteria (Gray, 1999). In addition to cyanobacterial-derived proteins, a number of non-cyanobacterial-like proteins are targeted to chloroplasts (Martin et al, 2002), implying that modern chloroplasts are maintained by processes that require both inherent prokaryotic systems and acquired eukaryotic systems (Gao et al, 2003; Hashimoto, 2003; Miyagishima et al, 2003; Chen C. et al, 2018; Lee and Hwang, 2018). Prokaryotes such as bacteria propagate by binary fission. In Escherichia coli, the oscillation of the MinCD complex, driven by the topological factor MinE through direct interaction between MinE and MinD, which causes its time-averaged concentration in the membrane to be highest at cell poles and lowest at the cell center, guides Z-ring formation in the midcell position (Bisicchia et al, 2013)
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