Studies On Molecular Mechanisms Of LPA1 In Regulating PSⅡ Assembly In Arabidopsis Thaliana

Photosystem II (PSII) is a multisubunit pigment-protein complex that catalyzes the light-driven water oxidation and reduction of plastoquinone. Because of the structural complexity of PSII, biogenesis and assembly of PSII requires the coordinated synthesis and assembly of both chloroplast- and nuclear-encoded proteins. These are likely to be a multi-step processes, which are assisted by many nuclear-encoded auxiliary and regulatory proteins. Until recently, the factors involved in regulating the biogenesis of PSII have remained largely unknown. Identification and characterization of these nuclear -encoded chloroplast proteins will increase our knowledge on molecular mechanisms of the PSII complexes biogenesis. To this purpose, we have screened PSII mutants with high chlorophyll fluorescence phenotypes from a collection of pSKI015 T-DNA-mutagenized Arabidopsis thaliana lines, and we further characterized the lpa1 mutant. The main results are summarized as follows:1. We have screened 62,000 T-DNA-mutagenized Arabidopsis thaliana lines and obtained 136 mutants with high chlorophyll fluorescence phenotype. Mutants with impaired energy transfer within PSII were identified based on the chlorophyll fluorescence induction kinetics. SDS-PAGE and immunoblot analyses indicated that the PSII subunits were reduced significantly and other complexes content were only affected slightly. These mutants with low photosystem II accumulation were nameded lpa mutants2. To gain insight into the processes involved in PSII biogenesis and maintenance, we characterized the lpa1 mutant of Arabidopsis thaliana, which generally accumulates lower than wild-type levels of the PSII complex. The pigment contents, relative growth were significantly reduced in the mutant. Analyses of the chlorophyll fluorescence induction and P700 redox kinetics showed that the mutants have defects in energy transfer within PSII. Immunoblot and BN-PAGE studies showed that the PSII can be assembled in the mutant, but the amounts of the PSII proteins were reduced to about 20% of wild-type levels. No alterations in the...