Mutations in AtpB and LexA confer temperature tolerance in an evolved Synechocystis sp. PCC 6803 strain resistant to high temperature and light

Outdoor-scale cultivation of cyanobacteria can encounter multiple stresses, including high temperature (HT) and excessive light (HL) exposure. In this study, we obtained HL and HT tolerant strains through adaptive laboratory evolution. The evolved strains (HLHT-1, HLHT-2, and HLHT-3) exhibited lower levels of ROS, improved photosynthetic performance and pigment levels, and greater dry weight and glycogen compared to the wild-type strain under HT and HL conditions. Comparative transcriptome analysis suggested that HLHT-2 possibly achieved high temperature resistance by up-regulating the expression of oxidative phosphorylation pathway or down-regulating the expression of peptidases and inhibitors pathway. Whole-genome re-sequencing identified a total of six mutations in the 3 evolved strains relative to the parent strain. Via gene knockout, inhibition, and overexpression of the mutated genes in parent strain, we found two genes contributing the HT tolerance including sll1626 encoding the SOS response inhibitory protein LexA, and slr1329 encoding the ATP synthase subunit AtpB. These findings provide valuable insights into the genetic basis of cross-stress tolerance in photosynthetic microorganisms and, given the shared evolutionary heritage between cyanobacteria and plant chloroplasts, may also inform strategies for engineering stress-resilient plants to enhance productivity under challenging environmental conditions.