PetM Is Essential for the Stabilization and Function of the Cytochrome b6f Complex in Arabidopsis

The cytochrome b(6)f (cyt b(6)f) acts as a common linker of electron transport between photosystems I and II in oxygenic photosynthesis. PetM, one of eight subunits of the cyt b(6)f complex, is a small hydrophobic subunit at the outside periphery, the functional mechanism of which remains to be elucidated in higher plants. In this work, we found that unlike the PetM mutant in Synechocystis sp. PCC 6803, the Arabidopsis thaliana PetM mutant showed a bleached phenotype with yellowish leaves, block of photosynthetic electron transport and loss of photo-autotrophy, similar to the Arabidopsis PetC mutant. Although PetM is relatively conserved between higher plants and cyanobacteria, Synechocystis PetM could not rescue the PetM-knockout phenotype in Arabidopsis. We provide evidence that the Synechocystis PetM did not stably bind to the Arabidopsis cyt b(6)f complex. Based on these results, we suggest that PetM is required by Arabidopsis to maintain the function of the cyt b(6)f complex, likely through its close link with core subunits to form a tight 'fence' that stabilizes the core of the complex.

Automated summary

The study revealed that the PetM mutant in Arabidopsis exhibited a similar phenotype to the PetC mutant, suggesting the crucial role of PetM in maintaining the function of the cyt b(6)f complex.