Improving tolerance to fluctuating light through adaptive laboratory evolution in the cyanobacterium Synechocystis
Fluctuating light (FL) poses a severe challenge to photosynthetic organisms like cyanobacteria, disrupting carbon assimilation and damaging photosystems. While key components of cyanobacterial FL tolerance have been identified, their genetic enhancement remains unexplored. We applied adaptive laboratory evolution to Synechocystis PCC 6803 under two complex FL regimes, including one lethal to the starter strain (LT), to generate FL-adaptive alleles. Our analysis revealed 44 fully segregated novel mutations in 24 monoclonal evolved strains, with 28 affecting proteins or structural RNAs. We focused on three mutations for further study. Mutations in Sll0518 and Pam68 (involved in PSII assembly) were present in all evolved strains, indicating early emergence. These mutations enhanced tolerance to non-lethal FL conditions when introduced into LT. A gain-of-function mutation in RpaB (regulator of phycobilisome association B), found in three strains tolerant to lethal FL, significantly increased tolerance to both lethal FL and high light conditions when introduced into LT. As RpaB has plant homologs, this finding could potentially be applied to enhance FL tolerance and photosynthetic efficiency in crops, offering new possibilities for improving agricultural productivity under variable light conditions.