CurT dosage quantitatively affects thylakoid structure and PSII performance in Synechocystis sp. PCC 6803

Abstract

The photosynthetic thylakoid membrane systems of many oxygenic photosynthesizers form elaborate three-dimensional structures. Curvature Thylakoid (CurT/CURT1) proteins are central regulators of thylakoid architecture in cyanobacteria and plants, driving both grana stacking and the formation of thylakoid convergence zones (TCZs) by promoting membrane curvature while also contributing to cyanobacterial cell and green-algal chloroplast division. While the functional role of grana stacks in terrestrial photosynthesis is well established, the physiological significance of cyanobacterial TCZs remains unclear. Here, we investigated the role of TCZs in Synechocystis sp. PCC 6803 by quantitatively assessing how CurT protein abundance shapes thylakoid membrane organization, TCZ frequency, and thylakoid layering, and how these architectural features relate to photosynthetic efficiency in a set of curT expression mutants. By correlating defined structural parameters of the thylakoid system with cellular CurT levels, we defined for the first time the quantitative relationship between CurT abundance, thylakoid architecture, and photosystem II (PSII) performance. Our results reveal a non-linear, logarithmic relationship: minimal CurT suffices to restore TCZ formation and sustain WT-like growth, while overexpression further enhances PSII activity and culture yield. Together, these findings identify CurT as a dose-dependent key determinant of thylakoid structure and underscore the functional importance of thylakoid membrane architecture for efficient photosynthesis. Significance StatementThis study assesses how the membrane-shaping protein CurT quantitatively regulates thylakoid architecture and photosynthetic performance in the model cyanobacterium Synechocystis sp. PCC 6803. By relating CurT abundance to the formation of thylakoid convergence zones, photosystem II efficiency, and growth rate, we provide evidence of CurT acting as a key regulator of cyanobacterial membrane organization in a dosage-dependent manner. Our findings provide insight into the structural basis and physiological relevance of thylakoid convergence zones and suggest CurT as a potential target for improving cyanobacterial light-energy conversion.