Single aminoacidic substitutions in the Chlamydomonas reinhardtii D1 protein affects photosynthesis efficiency, carotenoids and plastoquinone biosynthesis in physiological and stressful conditions
Amina Antonacci1, Maya Lambreva1, Sandro Pastorelli1, Andrea Margonelli1, Ivo Bertalan2, Udo Johanningmeier2, Maria Teresa Giardi1 and Giuseppina Rea1.
1) Institute of Crystallography (CNR), Via Salaria km 29.300, 00015 Monterotondo (Rm), Italy;
2) Plant Physiology Institute, Martin-Luther-University, Weinbergweg 10 D-06120 Halle, Germany
Analyses of C. reinhardtii strains mutated in the QB binding pocket of the D1 protein revealed the consequences of single amino acidic substitution on the overall photosynthetic process. During all developmental phases, D1 mutants accumulated lower amount of chlorophyll, and showed a reduction of the light absorption cross section compared to the reference strain, IL. Analyses of the light-dependence curves of the O2 evolution rate indicated the mutant highest light compensation point, supporting the hypothesis of a reduced antenna cross section. In addition, also the maximal quantum yield of photosystem II (Fv/Fm), electron transfer efficiency (1-Vj) and oxygen evolution capacity were remarkably decreased. Intriguingly, xanthophylls content of the peripheral antennae proteins was different among the D1 strains and in any case lower compared to IL. Comparative analyses of time-course carotenogenic gene expression profiles by Real-Time RT PCR, and photosynthetic pigment profile by HPLC in response to high photon fluency conditions evidenced a strong induction in lutein and zeaxanthin accumulation and corresponding biosynthetic genes, only in IL strain, in which also the xanthophylls cycle was activated. Also the plastoquinone biosynthesis genes were activated, in parallel with genes acting in the first steps of the carotenogenesis, hence, supporting the involvement of PQ in carotenoids biosynthesis. In the reaction centre core, accumulation levels of the gene encoding the D1 protein were strongly modulated. These results describe the dramatic changes generated by single amino acidic substitution in the D1 protein, and highlight the need to dissect the molecular mechanisms controlling plastid-nucleus communication.
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