Photosystem II (PSII) is the core of photosynthesis, and its key component, the D1 protein, is highly susceptible to oxidative damage under high light. Efficient PSII repair relies on the recognition, degradation, and replacement of the damaged D1 protein. The FtsH protease complex plays a central role in D1 degradation, but how its activity is precisely regulated and whether other auxiliary proteins are involved remain unclear.

TEF6, a member of the GreenCut protein family, is conserved among photosynthetic organisms and is localized to the thylakoid membrane. Studies have shown that plants lacking TEF6 exhibit growth inhibition and reduced PSII activity under high light, suggesting its potential involvement in light stress response or PSII repair. However, the specific molecular function and regulatory mechanism of TEF6 remain unclear. Therefore, elucidating the role of TEF6 in PSII repair is crucial for understanding the regulation of FtsH stability and the mechanisms underlying PSII quality control on the thylakoid membrane.

In a study published inPlant Communications, researchers from the Institute of Botany, Chinese Academy of Sciences, systematically revealed the key function of TEF6 protein in PSII repair, providing new mechanistic insights into how photosynthetic machinery responds to light stress.

Using Chlamydomonas reinhardtii as the experimental model, the researchers investigated the function of TEF6, a member of the GreenCut protein family, in PSII repair. They found that TEF6 is localized to the chloroplast thylakoid membrane and directly interacts with both the damaged D1 protein and the FtsH protease complex responsible for D1 degradation. TEF6 functions as a "scaffold protein," stabilizing the accumulation and localization of FtsH, thereby precisely regulating the degradation and replacement of D1.

Experimental results showed that the tef6 mutant exhibited severe growth inhibition, reduced stability of PSII supercomplexes, disordered thylakoid structure, and uncontrolled degradation of the D1 protein under high light. In the absence of TEF6, excessive accumulation of FtsH protease led to the over-degradation of D1, disrupting the PSII repair cycle and ultimately causing photoinhibition and cell death.

This study reveals a novel pathway mediated by the GreenCut protein to regulate PSII repair by stabilizing the protease complex, providing new molecular targets for improving photosynthetic efficiency and stress tolerance in crops.

"Our study not only identifies TEF6 as a novel regulator of PSII repair but also elucidates a new mechanism through which a scaffold protein stabilizes protease activity to maintain the homeostasis of the photosynthetic machinery," said YANG Wenqiang, corresponding author of the study and a researcher at the Institute of Botany, Chinese Academy of Sciences.