Chlorosis as developmental program in cyanobacteria: The proteomic fundament for surviving and awakening

Cyanobacteria that do not fix nitrogen adapt to prolonged periods of nitrogen deprivation in a chlorotic state where cell growth and metabolism is arrested. Upon nutrient availability, the cells return back to vegetative growth within 2-3 days. This resuscitation process is highly orchestrated and relies on the stepwise re-installation and activation of essential cellular structures and functions. We investigate transition into chlorosis and return to vegetative life as a simple model of a cellular developmental process that represents a fundamental survival strategy in biology. In the present study, we describe the process through quantitative proteomics and phosphoproteomics analysis of long-term nitrogen-starved Synechocystis sp. PCC 6803 cells during different time points of resuscitation. Intriguingly, substantial O phosphorylation of proteins involved in photosynthesis was detected in the chlorotic state, including hyperphosphorylation of the remaining phycobiliproteins. We provide evidence that hyperphosphorylation of the terminal rod linker CpcD increases the lifespan of phycobiliproteins during chlorosis.