LIL3, a light-harvesting-like protein, plays an essential role in chlorophyll and tocopherol biosynthesis
LIL3, a light-harvesting-like protein, plays an essential role in chlorophyll and tocopherol biosynthesis
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DOI：
10.1073/pnas.1004699107
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发表时间：
2010-09-21
影响因子：
11.1
通讯作者：
Tanaka, Ayumi
中科院分区：
文献类型：
--
作者：
Tanaka, Ryouichi;Rothbart, Maxi;Tanaka, Ayumi
光收集叶绿素结合蛋白（LHC）是真核生物光合机制的主要成分。在植物中，六组不同的蛋白质，LHC样蛋白质，与LHC共享一个保守基序。尽管LHC和LHC样蛋白的进化被认为是现代光合真核生物多样化的关键，但我们对LHC样蛋白的进化和功能的了解仍然有限。在这项研究中，我们旨在通过分析缺乏lhc样蛋白LIL3蛋白的拟南芥突变体，具体了解lhc样蛋白的功能。拟南芥基因组包含LIL3、LIL3:1和LIL3:2两个基因拷贝。在lil3:1/lil3:2双突变体中，大多数叶绿素分子与不饱和香叶醇侧链结合。这种突变体也缺乏a-生育酚。这些结果表明，在lil3突变体中，叶绿素的香叶醇侧链和生育酚生物合成的重要中间体——香叶醇焦磷酸的还原都受到了损害。我们发现，在lil3双突变体中，负责这些反应的香叶基香叶基还原酶的含量严重降低，而该酶的mRNA水平没有显著变化。我们通过分裂泛素测定、双分子荧光互补、蓝原生和SDS聚丙烯酰胺凝胶电泳，证明了香叶基香叶基还原酶与两种LIL3异构体的相互作用。我们认为LIL3通过稳定香叶基还原酶在功能上参与了叶绿素和生育酚的生物合成。
The light-harvesting chlorophyll-binding (LHC) proteins are major constituents of eukaryotic photosynthetic machinery. In plants, six different groups of proteins, LHC-like proteins, share a conserved motif with LHC. Although the evolution of LHC and LHC-like proteins is proposed to be a key for the diversification of modern photosynthetic eukaryotes, our knowledge of the evolution and functions of LHC-like proteins is still limited. In this study, we aimed to understand specifically the function of one type of LHC-like proteins, LIL3 proteins, by analyzing Arabidopsis mutants lacking them. The Arabidopsis genome contains two gene copies for LIL3, LIL3:1 and LIL3:2. In the lil3:1/lil3:2 double mutant, the majority of chlorophyll molecules are conjugated with an unsaturated geranylgeraniol side chain. This mutant is also deficient in a-tocopherol. These results indicate that reduction of both the geranylgeraniol side chain of chlorophyll and geranylgeranyl pyrophosphate, which is also an essential intermediate of tocopherol biosynthesis, is compromised in the lil3 mutants. We found that the content of geranylgeranyl reductase responsible for these reactions was severely reduced in the lil3 double mutant, whereas the mRNA level for this enzyme was not significantly changed. We demonstrated an interaction of geranylgeranyl reductase with both LIL3 isoforms by using a split ubiquitin assay, bimolecular fluorescence complementation, and combined blue-native and SDS polyacrylamide gel electrophoresis. We propose that LIL3 is functionally involved in chlorophyll and tocopherol biosynthesis by stabilizing geranylgeranyl reductase.