High light (HL) exposure leads to photoinhibition and excess accumulation of toxic reactive oxygen species (ROS) in photosynthetic organisms, negatively impacting the global primary production. In this study, by screening a mutant library, a gene related with bicarbonate transport, slr1512, was found involved in HL acclimation in model cyanobacterium Synechocystis sp. PCC 6803. Comparative growth analysis showed that the slr1512 knockout mutant dramatically enhanced the tolerance of Synechocystis towards long-term HL stress (200 μmol photons m⁻² s⁻¹) than the wild type, achieving an enhanced growth by ~1.95-folds after 10 d. The phenotype differences between Δslr1512 and the wild type were analyzed via absorption spectrum and chlorophyll a content measurement. In addition, the accessible bicarbonate controlled by slr1512 and decreased PSII activity were demonstrated, and they were found to be the key factors affecting the tolerance of Synechocystis against HL stress. Further analysis confirmed that intracellular bicarbonate can significantly affect the activity of photosystem II, leading to the altered accumulation of toxic ROS under HL. Finally, a comparative transcriptomics was applied to determine the differential responses to HL between Δslr1512 and the wild type. This work provides useful insights to long-term acclimation mechanisms towards HL and valuable information to guide the future tolerance engineering of cyanobacteria against HL.

高光（HL）暴露会导致光合作用中的光抑制和有毒活性氧（ROS）的过量积累，从而对全球初级生产产生负面影响。在这项研究中，通过筛选突变体文库，发现与碳酸氢盐转运相关的基因slr1512参与了模型蓝藻Synechocystis sp。的HL适应。PCC6803。比较生长分析表明，与野生型相比，slr1512敲除突变体显着增强了集囊藻对长期HL胁迫（200μmol光子m ^-2  s ^-1）的耐受性，实现了约1.95倍的增长10天 Δslr1512之间的表型差异通过吸收光谱和叶绿素a含量测量分析野生型。此外，还证实了由slr1512控制的可及的碳酸氢盐和PSII活性的降低，它们是影响集囊藻对HL胁迫耐受性的关键因素。进一步的分析证实，细胞内碳酸氢盐可以显着影响光系统II的活性，导致HL下有毒ROS的积累发生改变。最后，采用比较转录组学方法确定Δslr1512对HL的差异反应和野生型 这项工作为HL的长期适应机制提供了有用的见识，并为指导蓝细菌对HL的未来耐受工程提供了有价值的信息。