Chlorophyll plays an indispensable role in the light reaction of the photosynthesis. The adequate supply of chlorophyll is ensured by tetrapyrrole biosynthesis (TBS). Within the last decades, multiple proteins were identified, which are involved in adjusting the TBS-pathway to changing (a)biotic plant growth conditions. Nevertheless, it is not fully understood how the TBS-pathway is coordinated parallel to the assembly of the photosystems and the integration of chlorophylls into the pigment-binding subunits of the photosystems. Several years ago, an interaction partner of the protochlorophyllide-oxidoreductase (POR) was identified in Synechocystis which was proposed to be involved in the coordination of these mechanisms. The POR-INTERACTING TPR-Protein (Pitt) binds and stabilizes POR at the thylakoid membranes and interacts with the precursor protein of D1. Therefore, Pitt could facilitate the incorporation of chlorophylls into the plastid-encoded nascent photosynthetic subunits. Pitt belongs to the tetratricopeptide repeat (TPR) protein family, whose members mediate protein-protein-interactions. Besides the identification of the potential Pitt-homolog in the model organism Arabidopsis thaliana, analysis of additional members of the TPR-protein superfamily was a promising approach for the identification of further posttranslational regulators of TBS and photosynthesis. Five Arabidopsis thaliana TPR-proteins with a high sequence similarity to Pitt were selected. Four of those proteins are able to interact physically with POR. Among them, the TPR-protein encoded by the gene At1g78915 (TPR1) was the best candidate to represent a putative Pitt homolog in Arabidopsis. Similar to Pitt, TPR1 is a plastid-localized integral membrane protein, which interacts with POR at the thylakoid membranes. The stabilizing effect of TPR1 on POR is especially needed during etioliation and greening. Additionally, TPR1 is required for a inactivation of the 5'-aminolevulinic acid synthesis.
|Advisor:||Grimm , Bernhard , Buckhout , Thomas , Finkemeier , Iris|
|School:||Humboldt Universitaet zu Berlin (Germany)|
|Source:||DAI-C 81/7(E), Dissertation Abstracts International|
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