Genes encoding lipid II flippase MurJ and peptidoglycan hydrolases are required for chloroplast division in the moss Phy
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Genes encoding lipid II flippase MurJ and peptidoglycan hydrolases are required for chloroplast division in the moss Physcomitrella patens Hanae Utsunomiya1 · Nozomi Saiki1 · Hayato Kadoguchi2 · Masaya Fukudome2 · Satomi Hashimoto2 · Mami Ueda2 · Katsuaki Takechi3 · Hiroyoshi Takano3 Received: 24 July 2020 / Accepted: 2 October 2020 © Springer Nature B.V. 2020
Abstract Key message Homologous genes for the peptidoglycan precursor flippase MurJ, and peptidoglycan hydrolases: lytic transglycosylase MltB, and dd-carboxypeptidase VanY are required for chloroplast division in the moss Physcomitrella patens. Abstract The moss Physcomitrella patens is used as a model plant to study plastid peptidoglycan biosynthesis. In bacteria, MurJ flippase transports peptidoglycan precursors from the cytoplasm to the periplasm. In this study, we identified a MurJ homolog (PpMurJ) in the P. patens genome. Bacteria employ peptidoglycan degradation and recycling pathways for cell division. We also searched the P. patens genome for genes homologous to bacterial peptidoglycan hydrolases and identified genes homologous for the lytic transglycosylase mltB, N-acetylglucosaminidase nagZ, and ld-carboxypeptidase ldcA in addition to a putative dd-carboxypeptidase vanY reported previously. Moreover, we found a ß-lactamase-like gene (Pplactamase). GFP fusion proteins with either PpMltB or PpVanY were detected in the chloroplasts, whereas fusion proteins with PpNagZ, PpLdcA, or Pplactamase localized in the cytoplasm. Experiments seeking PpMurJ-GFP fusion proteins failed. PpMurJ gene disruption in P. patens resulted in the appearance of macrochloroplasts in protonemal cells. Compared with the numbers of chloroplasts in wild-type plants (38.9 ± 4.9), PpMltB knockout and PpVanY knockout had lower numbers of chloroplasts (14.3 ± 6.7 and 28.1 ± 5.9, respectively). No differences in chloroplast numbers were observed after PpNagZ, PpLdcA, or Pplactamase single-knockout. Chloroplast numbers in PpMltB/PpVanY double-knockout cells were similar to those in PpMltB single-knockout cells. Zymogram analysis of the recombinant PpMltB protein revealed its peptidoglycan hydrolase activity. Our results imply that PpMurJ, PpMltB and PpVanY play a critical role in chloroplast division in the moss P. patens. Keywords Chloroplast division · Lipid II flippase · Lytic transglycosylase · Peptidase · Physcomitrella patens
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11103-020-01081-0) contains supplementary material, which is available to authorized users. * Katsuaki Takechi ktakechi@kumamoto‑u.ac.jp * Hiroyoshi Takano takano@kumamoto‑u.ac.jp 1
Graduate School of Science and Technology, Kumamoto University, Kumamoto 860‑8555, Japan
2
Faculty of Science, Kumamoto University, Kumamoto 860‑8555, Japan
3
Faculty of Advanced Science and Technology, Kumamoto University, Kumamoto 860‑8555, Japan
Peptidoglycan forms a mesh-like sacculus surrounding the cytoplasmic membrane of almost all eubacteria
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