Cyanobacterial PSI assembly

Dai, Song, Xu et al. identify Ycf51 as a photosystem I assembly factor in cyanobacteria

https://doi.org/10.1093/plcell/koad330

By Guo-Zheng Dai, Central China Normal University

Question: Background: While the mechanisms of photosystem II biogenesis and the auxiliary proteins involved are well known, we know much less about photosystem I (PSI) assembly. Several PSI assembly factors exist only in plants but not in cyanobacteria (the presumptive ancestors of present-day chloroplasts), suggesting that there are differences in PSI assembly between cyanobacteria and plants. The initial aim of this study was to screen 12 hypothetical chloroplast reading frames (ycfs) that are conserved in Synechocystis sp. PCC 6803 for additional players in photosynthesis. This screen led to the identification of Ycf51 (Sll1702), a thylakoid membrane protein involved in Synechocystis PSI assembly.

Questions: How does ycf51 disruption affect PSI formation? What is the role of Ycf51 in PSI formation in cyanobacteria?

Findings: Ycf51 specifically localizes to thylakoid membranes, and its hydrophilic C terminus is exposed to the stroma. ycf51 disruption in Synechocystis leads to a strong decrease in PSI content, which impairs photoautotrophic growth. Ycf51 mediates PSI complex biogenesis at the post-translational level, while its disruption has little effect on PSI stability. Ycf51 cooperates with the PSI assembly factor Ycf3, but its absence does not negatively impact Ycf3 stability. Ycf51 also interacts with the PSI subunit PsaC, indicating its direct participation in PSI assembly.

Next steps: Future studies will aim to identify the PSI assembly intermediate, whose formation requires Ycf51 function, and to elucidate the interplay of the different accessory factors involved in cyanobacterial PSI assembly.

Reference:

Guo-Zheng Dai, Wei-Yu Song, Hai-Feng Xu, Miao Tu, Chen Yu, Zheng-Ke Li, Jin-Long Shang, Chun-Lei Jin, Chao-Shun Ding, Ling-Zi Zuo, Yan-Ru Liu, Wei-Wei Yan, Sha-Sha Zang, Ke Liu, Zheng Zhang, Ralph Bock, Bao-Sheng Qiu. (2024). Hypothetical chloroplast reading frame 51 encodes a photosystem I assembly factor in cyanobacteria. https://doi.org/10.1093/plcell/koad330