Translational control of the synthesis of the Euglena light harvesting chlorophyll a/ b binding protein of photosystem II

Abstract

Synthesis of the precursor to the light harvesting chlorophyll a/ b binding protein of photosystem II (LHCPII) increases 50–100-fold upon exposure of dark grown resting Euglena to light. LHCPII mRNA levels increase approximately two-fold upon light exposure indicating that LHCPII synthesis is controlled at the translational level. Approximately 68% of cellular LHCPII mRNA was associated with polysomes in dark grown resting cells. Light exposure had little effect on the relative amount of LHCPII polysomes indicating that light regulates pLHCPII synthesis at the level of polypeptide chain elongation. LHCPII synthesis is undetectable in that bleached Euglena mutants W 3BUL and W 10BSmL which lack detectable protochlorophyll(ide), the chloroplast photoreceptor and most if not all of the chloroplast genome. Over 60% of LHCPII mRNA was associated with polysomes in bleached mutants. LHCPII polysomes were membrane bound in wild type Euglena and bleached mutants maintained in the dark or the light. Photocontrol of Euglena LHCPII synthesis is probably mediated through the synthesis of a chloroplast generated signal which is required for release of signal recognition particle dependent arrest of LHCPII mRNA translation by membrane-bound polysomes.