G-Body, a Putative Germ Cell-Specific Organelle in Arabidopsis

Germ cell- specific organelles have been a research focus for decades and been well studied in animals. They often occur perinuclearly, are sometimes associated with mitochondria and play important roles in determining the properties of germ lines. More recent studies in animal germ-cell specific organelles also demonstrated their key functions in small RNA regulatory networks and DNA methylation. In plants, however, a germ cell-specific organelle has only been reported in very few observations.

During a large scale analysis of the Arabidopsis meiocyte-transcriptome and validation tests for candidate meiotically active promoters, we have observed a unique sub-cellular structure that accumulates Green Fluorescences Protein (GFP), which we refer to as  “G-body”. The G-body could be detected only in germ-cells from prophase I meiocytes to mature pollen of transgenic plants that carried plasmids of germ cell-specific promoters fused with the GFP gene. A single G-body per cell was observed and was found to be located at the perinuclear cytoplasm, which is easily distinguished by the intensity of fluorescence and the number of structures per cell.

Further pollen germination demonstrated the existence of the G-body in mature male gametophytes in some lines. Since the CDS-GFP fusion protein shows fluorescence predominantly in nuclei and the G-body can be observed mostly in promoter-only driven GFP plants, it is likely that the G-body plays a role in storing or processing non-functional protein during the male gametophyte development; other possible functions of animal germ-cell line organelles could perhaps also be connected to it.