Sll0528是集胞藻PCC6803中四个二位蛋白酶(site-2-protease, S2P)之一。本研究主要比较了三株集胞藻 （编码基因sll0528过表达的藻株OE0528，编码基因sll0528敲除的缺失藻株∆sll0528，以及野生型藻株）在不同氯化铵浓度下的生长表型。结果显示，缺失藻株∆sll0528对120 mM的氯化铵比野生型更敏感，光合系统损伤严重。在180 mM氯化铵下野生型株的生长受到抑制，而过表达藻株OE0528的生长优于野生型，更耐受高浓度铵盐，其光合系统色素藻蓝蛋白和叶绿素等的损伤程度低于野生型。可见，Sll0528在集胞藻PCC6803适应铵盐胁迫中发挥重要的作用，可能参与了铵盐胁迫的快速响应，并直接或间接介导高铵盐浓度下集胞藻对光合系统的保护或修复机制。本研究首次揭示了 S2P蛋白酶微藻具有一定的铵盐胁迫响应作用，相关结果对于深入探究微藻对铵盐的响应机制及提高微藻对铵盐的耐受性和利用率具有重要的意义。

Sll0528 is one of the site-2-protease (S2P) in Synechocystis sp. PCC 6803. In the work, the growth of three mutants of Synechocystis (the mutant overexpressed with OE0528 of the sll0528 gene, the ∆sll0528- knockout mutant, and the wild type) was compared under different concentrations of ammonium chloride. The results indicated that the knockout mutant ∆sll0528 was more sensitive to 120 mM ammonium chloride than the wild type, with the photosynthetic system damaged more seriously; at 180 mM ammonium chloride, the growth of wild type was inhibited, while the sll0528-overexpressed mutant OE0528 grew well, which showed higher toleration to the high concentration of ammonium, and better protection for the photosystem pigment phycocyanin and chlorophyll than the wild type. All the results suggested that Sll0528 plays an important role in the acclimation to ammonium stress in Synechocystis sp. PCC6803, probably through protected or recovered the photosystems under ammonium stress directly or indirectly. This is the first report to unveil the importance of S2P protease in ammonium stress of cyanobacteria, thus provding the base for the research of acclimation to ammonium stress and improvement of ammonium tolerance and utilization in microalgae in the future.

国家自然科学基金面上项目（31270085）