Normal oil body formation in Marchantia polymorpha requires functional coat protein complex I proteins

Abstract

Eukaryotic cells possess endomembrane organelles equipped with specific sets of proteins, lipids, and polysaccharides that are fundamental for realizing each organelle’s specific function and shape. A tightly regulated membrane trafficking system mediates the transportation and localization of these substances. Generally, the secretory/exocytic pathway is responsible for transporting cargo to the plasma membrane and/or the extracellular space. However, in the case of oil body cells in the liverwort Marchantia polymorpha, the oil body, a liverwort-unique organelle, is thought to be formed by secretory vesicle fusion through redirection of the secretory pathway inside the cell. Although their formation mechanism remains largely unclear, oil bodies exhibit a complex and bumpy surface structure. In this study, we isolated a mutant with spherical oil bodies through visual screening of mutants with abnormally shaped oil bodies. This mutant harbored a mutation in a coat protein complex I (COPI) subunit MpSEC28, and a similar effect on oil body morphology was also detected in knockdown mutants of other COPI subunits. Fluorescently tagged MpSEC28 was localized to the periphery of the Golgi apparatus together with other subunits, suggesting that it is involved in retrograde transport from and/or in the Golgi apparatus as a component of the COPI coat. The Mpsec28 mutants also exhibited weakened stiffness of the thalli, suggesting impaired cell–cell adhesion and cell wall integrity. These findings suggest that the mechanism of cell wall biosynthesis is also involved in shaping the oil body in M. polymorpha, supporting the redirection of the secretory pathway inward the cell during oil body formation.

Regulation of ROP GTPase cycling between active/inactive states is essential for vegetative organogenesis inMarchantia polymorpha

“…Given the abnormalities observed in gemma size in the single mutants of Mp REN and double mutants of Mp ROPGAP and Mp REN (Figure 2U), we performed a more detailed observation of gemma morphology. The wild-type gemmae had a flattened structure with two apical notches and dispersed oil bodies, predominantly in the margins (Figures 3A, F, and P; Kanazawa et al 2022). The gemmae of the single Mp ropgap ge mutant exhibited a flattened structure with two apical notches, similar to those of the wild-type gemmae (Figures 3B, G and P).…”

Dynamic Regulation of Lipid Droplet Biogenesis in Plant Cells and Proteins Involved in the Process

“…A recent study demonstrated that COPI may contribute to the acceptance of compatible pollen grains [ 100 ]. In liverwortare, analysis of a Marchantia polymorpha T-DNA-mutant with LDs with increased circularity confirmed that COPI subunit MpSEC28 is responsible for this phenotype and that normal LD formation requires COPI-mediated secretory activity [ 12 ]. However, it is unclear whether COPI plays a role in LD budding in other plant species.…”

“…Homologs of some regulatory proteins related to animal LD formation have been identified in plants, however, there is no experimental evidence to show whether they function the same way in plant LD formation [ 11 , 12 , 13 ]. It has been shown that plant and animal LD surface proteins are completely different ( Figure 1 ).…”