Functional Dissection of the Chlorophyll Dephytylation-Rephytylation Module

叶绿素(Chl)是组装在光合作用蛋白质复合体中的一种必需色素，吸收太阳辐射可见光光谱中的光子。在不利的光强或温度下，氧合光合作用容易受到过度激发的CHL所产生的活性氧物种的光损伤。光系统II(PSII)的D1核心蛋白最容易受到光损伤，但通过用新合成的蛋白质替代受损的蛋白质和重新组装新的Chl分子，在PSII/D1循环过程中被修复。Chl可以通过四吡咯生物合成途径中的从头合成或通过Chl循环来提供。最近发现了编码叶绿素DEPHYTYLASE 1(CLD1)的基因，从而阐明了这种新的酶在Chl循环或/和Chl降解中所起的作用。这一新的建议致力于揭示由CLD进行的Chl去植化和由Chl合成酶进行的重新植化在D1修复循环和其他叶绿素结合蛋白的Chl组装中的重要性。任何一种酶的中断都会影响光合作用的效率和抗逆性。但Chl循环的分子细节尚未阐明。本研究的目的是：(1)阐明三种不同的CLD亚型在植物叶片发育和种子成熟过程中的具体作用；(2)除脱镁叶绿酸a加氧酶(PAO)/叶绿球蛋白途径外，评估CLD对Chl降解的贡献，并验证CLD和Chl合成酶的相互作用蛋白，这可能有助于Chl的循环。这些研究将允许验证工作假说，即CLD亚型是PSII修复/重组过程中叶绿素循环的一部分。此外，它有望发现新的相互作用的蛋白质和这一过程的辅助因素，并预测导致Chl拆解和重组的生化过程的顺序。这些知识将有利于未来生物技术在作物上的应用，包括光合作用效率、产量提高和对不断变化的环境的适应研究。

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.