Rong Liwei, An Junhang, Chen Xinyue, Wang Chao, Wu Jianghao, Wang Peng, Zheng Yongxing, Wang Xin, Chai Xin, Li Wei, Hu Zhubing, Lu Dandan, Chen Guangyu E, Ouyang Min, Grimm Bernhard, Zhang Lixin, Xu Xiumei
The Zhongzhou Laboratory for Integrative Biology, State Key Laboratory of Crop Stress Adaptation and Improvement, Henan Key Laboratory of Synthetic Biology and Biomanufacturing, School of Life Sciences, Henan University, Kaifeng 475004, China.
Sanya Institute, Henan University, Sanya 572025, China.
Plant Cell. 2025 Apr 2;37(4). doi: 10.1093/plcell/koaf068.
Chlorophyll biosynthesis must be tightly coupled to light-harvesting chlorophyll a/b-binding protein (LHCP) biogenesis, as free chlorophyll and its precursors are phototoxic. However, precisely how these 2 processes are coordinated in Arabidopsis (Arabidopsis thaliana) remains elusive. Our previous studies demonstrated the role of LHCP TRANSLOCATION DEFECT (LTD) in delivering LHCPs to the chloroplast via the signal recognition particle-dependent pathway. Here, we show that LTD interacts with and stabilizes the chlorophyll biosynthesis enzymes Mg-protoporphyrin methyltransferase and Mg-protoporphyrin monomethylester (MgPME) cyclase, maintaining their activity. We also demonstrate the direct binding of LTD to MgPME, and through crystal structure analysis, we show that the groove of the LTD dimer is critical for MgPME binding. Thus, we propose that LTD transfers MgPME from Mg-protoporphyrin methyltransferase to the MgPME cyclase. These results elucidate a role for LTD in synchronizing chlorophyll biosynthesis with LHCP transport to ensure the correct insertion of chlorophylls into LHCPs.
叶绿素生物合成必须与光捕获叶绿素a/b结合蛋白（LHCP）的生物合成紧密耦合，因为游离叶绿素及其前体具有光毒性。然而，在拟南芥中这两个过程究竟是如何协调的仍不清楚。我们之前的研究证明了LHCP易位缺陷（LTD）在通过信号识别颗粒依赖途径将LHCP转运到叶绿体中的作用。在此，我们表明LTD与叶绿素生物合成酶镁原卟啉甲基转移酶和镁原卟啉单甲酯（MgPME）环化酶相互作用并使其稳定，维持它们的活性。我们还证明了LTD与MgPME的直接结合，并且通过晶体结构分析表明，LTD二聚体的凹槽对于MgPME结合至关重要。因此，我们提出LTD将MgPME从镁原卟啉甲基转移酶转移到MgPME环化酶。这些结果阐明了LTD在使叶绿素生物合成与LHCP转运同步以确保叶绿素正确插入LHCP中的作用。
