Developing prolamine protein bodies are associated with the cortical cytoskeleton in rice endosperm cells

The mRNAs that encode the prolamine storage proteins in rice (Oryza sativa L.) endosperm cells are enriched on the surface of the prolamine protein bo dies (PBs), a subcellular structure consisting of a prolamine intracisterna l granule surrounded by rough endoplasmic reticulum membrane. Previous bioc hemical studies (D.G. Muench et al., 1998, Plant Physiol. 116: 559-569) hav e shown that prolamine mRNAs may be anchored to the PB surface via the cyto skeleton. To better understand the mechanism and role of mRNA localization in rice endosperm cells, we studied the subcellular development of prolamin e PBs and their relationship with the cytoskeleton in rice endosperm cells. Confocal microscopy of endosperm cells showed that, unlike the glutelin PB s, the developing prolamine PBs are not randomly distributed within the cel l, but instead are often enriched in the cortical region of the cell only a few micrometers beneath the plasma membrane. In addition, the peripheral p rolamine PBs are closely associated with the cortical microtubule and actin filament networks. The cortical enrichment of rice prolamine protein bodie s represents a unique example of endoplasmic reticulum subdomain localizati on in plant cells. The interaction of this endoplasmic reticulum subdomain with the cytoskeleton provides new insights on the possible mechanism and r ole of mRNA localization in plants.