PDV1 and PDV2 Differentially Affect Remodeling and Assembly of the Chloroplast DRP5B Ring.

Chloroplasts divide by binary fission, which is driven by a ring-like multiprotein complex spanning the inner and outer envelope membranes (OEMs) at the division site. The cytosolic DYNAMIN-RELATED PROTEIN 5B (DRP5B/ARC5) is a mechanochemical GTPase involved in binary fission of the chloroplast membrane in Arabidopsis (Arabidopsis thaliana), but the dynamics of its interactions with the chloroplast membranes and their regulation by guanine nucleotides and protein effectors remain poorly characterized. Using an Arabidopsis phot2 mutant with defects in chloroplast photorelocation movement, we determined that the ring structures of DRP5B at the chloroplast division site underwent subunit exchange with a cytosolic DRP5B pool. Mutant DRP5B proteins with impaired GTPase activity retained the ability to self-assemble at the constriction sites of chloroplasts, but did not rescue the chloroplast division defects in the Arabidopsis drp5B mutant. Our in vivo kinetic measurements of the DRP5B mutant T82D suggested that turnover of the DRP5B ring at the chloroplast division site is coupled to GTP hydrolysis. Furthermore, we established that DRP5B targeting to the chloroplast surface and assembly into a ring structure at the division site are specifically determined by the chloroplast outer OEM protein PLASTID DIVISION2 (PDV2), and that DRP5B-OEM dissociation is mainly mediated by PDV1, a paralog of PDV2. Thus, this study suggests that the mechanochemical properties of DRP5B on the chloroplast surface are dynamically regulated by its GTPase activity and major binding partners.

Clinical practice of Chinese medicine navel therapy for chronic diarrhea: A literature review.

Chronic diarrhea is one of the most common complaints in clinical practice for both adults and children. The purpose of this study was to assess the commonly used Chinese herbal medicine navel therapy for the treatment of chronic diarrhea (traditional Chinese medicine syndrome of spleen deficiency). The literature search was up to June 2018. Four types of studies (clinical trials, case series, case reports, and experts' experience) researched on Chinese medicine navel therapy used alone or combined with other therapies for the treatment of chronic diarrhea all included. Information on prescriptions, effectiveness, and safety of intervention was collected. Traditional Chinese Medicine Inheritance Support System V2.5 was used to do data analysis. We included 416 studies. All these studies carried out in 194 cities of China. We obtained the most commonly used single herbs, herbal medicine combination, and Chinese patent medicine for both adults and children. The top 3 single herbs were Caryophylli Flos (Dingxiang), Cinnamomi Cortex (Rougui), and Euodiae Fructus (Wuzhuyu). The most frequently used Chinese patent medicines were Ding Gui Infantile Navel Paste and Huoxiang Zhengqi Liquid. The effectiveness assessment was based on clinical trials, but we did not perform a meta-analysis because of different study design and unsatisfactory methodological quality. No serious adverse reaction happened in original studies. The application of Chinese medicine navel therapy could be one of the ideal treatments for chronic diarrhea in the future, especially for children. However, high-quality studies are very needed to provide clear evidence.

MCD1 Associates with FtsZ Filaments via the Membrane-Tethering Protein ARC6 to Guide Chloroplast Division.

Chloroplasts replicate by binary fission, a process driven by ring-like dynamic division machinery at mid-chloroplast. In Arabidopsis thaliana, the first molecular assembly of this machinery, the Z-ring, forms via the association of FtsZ1 and FtsZ2 heteropolymers with the inner envelope membrane through the membrane-tethering protein ACCUMULATION AND REPLICATION OF CHLOROPLASTS6 (ARC6). Spatial control of Z-ring assembly ensures the correct placement of the division machinery and, therefore, symmetric chloroplast division. The plant-specific protein MULTIPLE CHLOROPLAST DIVISION SITE1 (MCD1) plays a role in Z-ring positioning and chloroplast division site placement, but its mechanism of action is unknown. Here, we provide evidence that MCD1 is a bitopic inner membrane protein whose C terminus faces the chloroplast stroma. Interaction analysis showed that MCD1 and ARC6 directly interact in the stroma and that MCD1 binds to FtsZ2 in an ARC6-dependent manner. These results are consistent with the in vivo observation that ARC6 influences the localization of MCD1 to membrane-tethered FtsZ filaments. Additionally, we found that MCD1 is required for the regulation of Z-ring positioning by ARC3 and MinE1, two components of the chloroplast Min (minicell) system, which negatively regulates Z-ring placement. Together, our findings indicate that MCD1 is part of the chloroplast Min system that recognizes membrane-tethered FtsZ filaments during chloroplast division-ring positioning.