Poster: Organelle Biogenesis

Abs # 1131: Localization of chloroplast proteins to the Euglena nucleus

Presenter:	Schwartzbach, Steven D, sdschwrt@memphis.edu
Authors	Schwartzbach, Steven D (A) (B)  Weatherman, Aaron  (B)   Oasafune, Tetsuaki  (C)
Affiliations:	(A): Microbiology and Molecular Cell Sciences, University of Memphis (B): School of Biological Sciences, University of Nebraska (C): Department of Life Sciences, Nippon Sport Science University

Precursors to the Euglena chlorophyll a/b binding protein (pLHCPII) and small subunit of ribulose-bis-phosphate carboxylase (pSSU) are polyproteins transported in vesicles from the ER to the Golgi to the plastid where processing to mature SSU and LHCPII occurs. Immunoelectron microscopy (IM) localizes SSU and LHCPII in light exposed cells to a membranous cytoplasmic osmiophilic structure (COS), the Golgi and plastid. IM never finds SSU and LHCPII in the nucleus or cytoplasm of greening cells. Euglena cultured in the dark without aeration accumulates lipid. Upon aeration in the dark, lipid decreases, SSU accumulates, the proplastids expand with limited prothylakoid formation, chlorophyll is not produced and the integrity of the plastid envelope is disrupted. In addition to localizing to the COS, vacuolar structures and developing plastids, SSU is found in the nucleus. Incubation at 15 C blocks Golgi to plastid transport inhibiting light induced plastid development, chlorophyll synthesis, and LHCPII accumulation. IM of 15 C cells localizes LHCPII to the nucleus, COS, Golgi and to plastids with disrupted envelopes. Western blotting finds identical pLHCPII levels at 15 C and 26 C while mature LHCPII accumulates slower and to lower levels at 15 C. Since mature LHCPII and SSU accumulate at 15 C and in aerated high lipid cells, the nuclear localized proteins appear to have been initially targeted to the plastid. Nuclear localization of chloroplast proteins is only seen when normal plastid development is prevented resulting in disruption of the plastid envelope. Inhibition of normal development appears to lead to a loss of plastid integrity and release of plastid proteins to the cytoplasm with their subsequent diffusion into the nuclear compartment.