Functional Dissection of the Chlorophyll Dephytylation-Rephytylation Module

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Chlorophyll (Chl) is an essential pigment assembled in photosynthetic protein complexes and absorbs photons from the visible spectrum of solar radiation. Oxygenic photosynthesis at adverse light intensities or temperatures is prone to photodamage by reactive oxygen species which are generated as result of overexcited Chls. The D1 core protein of photosystem II (PSII) is most vulnerable to photodamage, but is repaired in a PSII/D1 recycle process through the substitution of damaged proteins with newly synthesized proteins and the reassembly of new Chl molecules. Chl could be supplied through the de novo synthesis in the tetrapyrrole biosynthetic pathway or by Chl recycling. The gene encoding a CHLOROPHYLL DEPHYTYLASE1 (CLD1) was recently identified allowing the elucidation of the role of this new enzyme for Chl recycling or/and Chl degradation. This new proposal is dedicated to unravel the importance of Chl dephytylation by CLD and rephytylation by Chl synthase for the D1 repair cycle and the Chl assembly of other chlorophyll-binding proteins. Interruption of either enzyme affects the photosynthesis efficiency and stress-tolerance. But the molecular details of Chl recycling are not elucidated. It is aimed (i) to clarify the specific roles of the three different CLD isoforms during plant development in leaves and seed maturation, (ii) to assess the contribution of CLD for Chl degradation apart from the well described pheophorbide a oxygenase (PAO)/phyllobilin pathway and to verify the interacting proteins of CLD and Chl synthase, which likely contribute to the Chl recycling. These studies will allow to verify the working hypothesis that the CLD isoforms are part of chlorophyll recycling during PSII repair/reassembly. Moreover, it is expected to identify novel interacting proteins and auxiliary factors of this process and to predict the order of biochemical processes leading to Chl disassembly and reassembly. This knowledge will be advantageous for future biotechnological application on crop plants, including studies on photosynthesis efficiency, yield improvement and acclimation to the changing environment.