Functional Dissection of the Chlorophyll Dephytylation-Rephytylation Module

叶绿素（Chl）是组成光合蛋白复合体的一种必需色素，吸收来自太阳辐射可见光谱的光子。在不利的光强或温度下，氧光合作用容易受到活性氧的光损伤，活性氧是由于过度激发chl而产生的。光系统II （PSII）的D1核心蛋白最容易受到光损伤，但在PSII/D1循环过程中，通过新合成的蛋白质取代受损的蛋白质和新的Chl分子的重组来修复。Chl可通过四吡咯生物合成途径的从头合成或Chl循环供给。最近发现了叶绿素去phytylase1 （CLD1）的编码基因，从而阐明了这种新酶在Chl循环或/和Chl降解中的作用。这一新的提议致力于揭示Chl合成酶对D1修复周期和其他叶绿素结合蛋白的Chl组装的重要性。任何一种酶的中断都会影响光合效率和抗逆性。但Chl再循环的分子细节尚未阐明。本研究的目的是(i)阐明三种不同的CLD亚型在植物叶片和种子成熟发育过程中的具体作用，（ii）评估CLD对Chl降解的贡献，除了已经描述好的酚a加氧酶(PAO)/叶茶绿素途径，并验证CLD和Chl合成酶的相互作用蛋白，这些蛋白可能有助于Chl的再循环。这些研究将验证CLD同工异构体是PSII修复/重组过程中叶绿素循环的一部分的工作假设。此外，还有望鉴定出这一过程中新的相互作用蛋白和辅助因子，并预测导致Chl拆卸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、产量提高和适应环境变化的研究。

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.