The processes involved in sexual reproduction have been diversified during plant evolution. Whereas charales, bryophytes, pteridophytes, and some gymnosperms utilize motile sperm as male gametes, in other gymnosperms and angiosperms the immotile sperm cells are delivered to the egg cells through elongated pollen tubes. During formation of the motile sperms, cells undergo a dynamic morphological transformation including drastic changes in shape and the generation of locomotor architecture. The molecular mechanism involved in this process remains mostly unknown. Membrane trafficking fulfills the exchange of various proteins and lipids among single membrane-bound organelles in eukaryotic cells, contributing to various biological functions. RAB GTPases and SNARE proteins are evolutionarily conserved key machineries of membrane trafficking mechanisms, which regulate tethering and fusion of the transport vesicles to target membranes. Our observation of fluorescently tagged plasma membrane-resident SNARE proteins demonstrated that these proteins relocalize to spherical structures during the late stages in spermiogenesis. Similar changes in subcellular localization were also observed for other fluorescently tagged SNARE proteins and a RAB GTPase, which acts on other organelles including the Golgi apparatus and endosomes. Notably, a vacuolar SNARE, MpVAMP71, was localized on the membrane of the spherical structures. Electron microscopic analysis revealed that there are many degradation-related structures such as multi-vesicular bodies, autophagosomes, and autophagic bodies containing organelles. Our results indicate that the cell-autonomous degradation pathway plays a crucial role in the removal of membrane components and the cytoplasm during spermiogenesis of Marchantia polymorpha. This process differs substantially from mammalian spermatogenesis in which phagocytic removal of excess cytoplasm involves neighboring cells.
This is a preview of subscription content, log in to check access.
We thank Dr. Atsuko Era for sharing unpublished results. This work was supported by Grants-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science, and Technology of Japan and by a Grant-in-Aid for JSPS Fellows (N.M. and T.K.). This research was also supported by JST, PRESTO.
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
Chiyoda S, Ishizaki K, Kataoka H, Yamato KT, Kohchi T (2008) Direct transformation of the liverwort Marchantia polymorpha L. by particle bombardment using immature thalli developing from spores. Plant Cell Rep 27:1467–1473. doi:10.1007/s00299-008-0570-5CrossRefPubMedGoogle Scholar
Doelling JH, Walker JM, Friedman EM, Thompson AR, Vierstra RD (2002) The APG8/12-activating enzyme APG7 is required for proper nutrient recycling and senescence in Arabidopsis thaliana. J Biol Chem 277:33105–33114. doi:10.1074/jbc.M204630200CrossRefPubMedGoogle Scholar
Ishizaki K, Chiyoda S, Yamato KT, Kohchi T (2008) Agrobacterium-mediated transformation of the haploid liverwort Marchantia polymorpha L., an emerging model for plant biology. Plant Cell Physiol 49:1084–1091. doi:10.1093/pcp/pcn085CrossRefPubMedGoogle Scholar
Kubota A, Ishizaki K, Hosaka M, Kohchi T (2013) Efficient agrobacterium-mediated transformation of the liverwort Marchantia polymorpha using regenerating thalli. Biosci Biotechnol Biochem 77:167–172. doi:10.1271/bbb.120700CrossRefPubMedGoogle Scholar