Light-independent biosynthesis and assembly of the photosystem II complex in the diatom Chaetoceros gracilis

• Diatoms can survive for long periods in the dark.
• Protein biosynthesis in dark-adapted cells is poorly understood.
• Radiolabeling pattern of PSII was changed in the dark but PSII dimer still formed.
• Carbon-fixing and light-harvesting components were hardly radiolabeled in the dark.
• Diatoms may regulate photosynthetic-protein biosynthesis in long-term dark survival.

Diatoms can survive for long periods in the dark. However, how biosynthesis of photosynthetic proteins contributes to survival in the dark is poorly understood. Using a radiolabeling technique, we examined whether de novo biosynthesis and assembly of photosynthetic proteins differs in light-adapted vs. dark-adapted marine diatoms (Chaetoceros gracilis). In light-adapted cells, D1 protein was heavily radiolabeled owing to rapid turnover of photosystem II (PSII). In dark-adapted cells (>24 h), the radiolabeling patterns of PSII components changed, but the PSII dimer still formed. Therefore, diatoms may regulate the biosynthesis of photosynthetic proteins for long-term survival in the dark.