The changes of PSII supercomplex stoichiometry in egy1 mutans are related to chlorophyll b deficiency

EGY1 is a chloroplast metalloprotease, the physiological role of which remains elusive. The changes observed in physiology and gene expression in egy1 mutants indicate that lack of the protease leads to yellow-green phenotype, changes in stoichiometry in PSII complexes, and early senescence. However, the knowledge concerning the role of the EGY1 to maintain the PSII function remains elusive. The aim of our study was to gain a deeper insight into the role of EGY1 protease in maintaining proper stoichiometry of PSII complexes. We applied the blue native electrophoresis technique as well as the immunoblotting method to investigate the abundance of PSII supercomplexes and selected individual PSII apoproteins in two Arabidopsis thaliana egy1 mutant lines. We also performed analyses of photosynthetic pigment content using DMSO assay. All analyses were performed in three biological replicates. Our results revealed reductions in contents of LHCII trimers and monomers in both egy1 mutant lines, as well as lower accumulation levels of Lhcb1 and Lhcb2 (but not Lhcb3) apoproteins. These changes were accompanied by an increased chlorophyll a/b ratio. We conclude that the observed pattern of changes in PSII stoichiometry is related to chlorophyll b deficiency. This reduction of chlorophyll b content is not, however, related to chlorophyllide a oxygenase abundance.

Automated summary

The study revealed that EGY1 protease plays a crucial role in maintaining the stoichiometry of PSII complexes, with its deficiency leading to changes in PSII complexes, premature senescence, and decreased chlorophyll content. This reduction is related to chlorophyll b deficiency and not to chlorophyllide a oxygenase abundance.