Regulation of the Synthesis and assembly of the phofosynthesis protein of Euglena

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Precursors to the Euglena chlorophyll a/b binding protein (pLHCPII) and small subunit of ribulose-bis-phosphate carboxylase (pSSU) are transported in vesicles from ER to Golgi to chloroplast. Immunoelectron microscopy (IM) localizes SSU and LHCPII in greening cells to a membranous cytoplasmic osmiophilic structure (COS), the Golgi and chloroplast but never the nucleus or cytoplasm. Euglena cultured in the dark without aeration accumulate lipid. Upon aeration, lipid decreases, SSU accumulates and proplastids expand with limited prothylakoid formation. IM localizes SSU to the nucleus, COS, vacuolar structures and developing plastids of dark aerated cells. 15 C blocks Golgi to chloroplast transport inhibiting light induced chloroplast development and LHCPII accumulation. IM localizes LHCPII to the nucleus, COS, Golgi and plastids of 15 C cells. Western blotting demonstrates that pLHCPII levels are identical at 15 and 26 C while mature LHCPII accumulates slower and to lower levels at 15 C.Taken together, these experiments suggest that nuclear localization of chloroplast proteins is associated with disruption of normal plastid development. Chloroplast proteins are localized to the nucleus either by vesicle mistargeting or as is more likely through disruption of chloroplast integrity, release of chloroplast proteins to the cytoplasm and their subsequent diffusion into the nuclear compartment.