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.

适应氮波动环境的机制对于水生蓝藻在自然栖息地的生存是必要的，但我们的理解还远未完成。在这里，藻胆蛋白的合成被证实比氮失绿恢复过程中光系统成分的合成要早得多，并且发现一种未知的蛋白质Ssr1698参与了这一合成过程。该未知蛋白被进一步鉴定为四吡咯生物合成途径中的c型血红素加氧酶( c HO)，并催化血红素环打开形成胆绿素IXα，胆绿素IXα是藻胆素产生和随后的藻胆蛋白合成所必需的。此外，c H2O 依赖性藻胆蛋白分别通过其氮储存和光捕获功能，在失绿和复绿过程中对蓝藻细胞的生长至关重要。总的来说，在光合生物中从氮失绿恢复过程中优先表达的c H2O 被确定，并且这种酶依赖性藻胆蛋白的双重功能被认为是水生蓝藻适应氮波动环境的重要机制。