School of Ecological and Environmental Sciences, East China Normal University, 200241, Shanghai, China.
College of Life Sciences, Shanghai Normal University, 200234, Shanghai, China.
Commun Biol. 2023 Sep 15;6(1):944. doi: 10.1038/s42003-023-05315-x.
The mechanisms of acclimating to a nitrogen-fluctuating environment are necessary for the survival of aquatic cyanobacteria in their natural habitats, but our understanding is still far from complete. Here, the synthesis of phycobiliprotein is confirmed to be much earlier than that of photosystem components during recovery from nitrogen chlorosis and an unknown protein Ssr1698 is discovered to be involved in this synthetic process. The unknown protein is further identified as a c-type heme oxygenase (cHO) in tetrapyrrole biosynthetic pathway and catalyzes the opening of heme ring to form biliverdin IXα, which is required for phycobilin production and ensuing phycobiliprotein synthesis. In addition, the cHO-dependent phycobiliprotein is found to be vital for the growth of cyanobacterial cells during chlorosis and regreening through its nitrogen-storage and light-harvesting functions, respectively. Collectively, the cHO expressed preferentially during recovery from nitrogen chlorosis is identified in photosynthetic organisms and the dual function of this enzyme-dependent phycobiliprotein is proposed to be an important mechanism for acclimation of aquatic cyanobacteria to a nitrogen-fluctuating environment.
适应氮素波动环境的机制对于水生蓝藻在其自然栖息地中的生存是必要的，但我们的理解还远远不够。在这里，藻胆蛋白的合成被确认为在从氮饥饿中恢复时比光合系统组件更早，并且发现一个未知蛋白 Ssr1698 参与了这个合成过程。该未知蛋白进一步被鉴定为四吡咯生物合成途径中的 c 型血红素加氧酶 (cHO)，并催化血红素环的打开以形成胆绿素 IXα，这是藻胆蛋白生产和随后的藻胆蛋白合成所必需的。此外，通过其氮储存和光捕获功能，发现 cHO 依赖性藻胆蛋白对于蓝藻细胞在黄化和返绿过程中的生长是至关重要的。总的来说，在从氮饥饿中恢复时优先表达的 cHO 在光合生物中被鉴定出来，并且提出了这种酶依赖性藻胆蛋白的双重功能是水生蓝藻适应氮素波动环境的重要机制。
