Loss-Function of EGY1 Results in Photosynthesis Damage through Reducing Stability of Photosystem II in Arabidopsis thaliana

In egy1 (ethylene-dependent gravitropism-deficient and yellow-green 1) mutants of Arabidopsis thaliana (L.) Heynh., there is reduced granal thylakoids, smaller size and less number of plastids in endodermal cells, suggesting that EGY1 protein is required for chloroplast development. Chloroplast is the apparatus of photosynthesis, how do egy1 mutants affect photosynthesis? Here we have further characterized the function of EGY1 protein in photosynthesis. The chlorophyll content and Fv/Fm (maximum photochemical efficiency of PSII) decreased much more rapidly with increasing leaf age in egy1 mutants than in wild-type (WT) plants of A. thaliana. The results of blue native-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (BN-SDS-PAGE) suggested that EGY1 was associated with photosystem II (PSII) supercomplexes. The spectroscopic and immunoblot analyses further showed that accelerated reductions in the abundance of D1, D2 and light harvesting complex II (LHCII) occurred with increasing leaf age in egy1 mutants. Moreover, PSII proteins (D1 and LHCII) were less stable in egy1 mutants than in WT plants under high light condition. Pull-down assays showed that EGY1 was colocalized with D2 protein. These results showed that loss-function of EGY1 results in accelerated reduction of PSII and in decreased stability of PSII, suggesting that defection of EGY1 results in impaired photosynthesis through breaking down the interaction of EGY1 with PSII in A. thaliana.