Biology Department, Life and Environmental College, Shanghai Normal University, Shanghai 200234, China.
Plant Physiol. 2011 Jan;155(1):130-41. doi: 10.1104/pp.110.165589. Epub 2010 Nov 19.
In land-plant chloroplasts, the grana play multiple roles in photosynthesis, including the potential increase of photosynthetic capacity in light and enhancement of photochemical efficiency in shade. However, the molecular mechanisms of grana formation remain elusive. Here, we report a novel gene, Grana-Deficient Chloroplast1 (GDC1), required for chloroplast grana formation in Arabidopsis (Arabidopsis thaliana). In the chloroplast of knockout mutant gdc1-3, only stromal thylakoids were observed, and they could not stack together to form appressed grana. The mutant exhibited seedling lethality with pale green cotyledons and true leaves. Further blue native-polyacrylamide gel electrophoresis analysis indicated that the trimeric forms of Light-Harvesting Complex II (LHCII) were scarcely detected in gdc1-3, confirming previous reports that the LHCII trimer is essential for grana formation. The Lhcb1 protein, the major component of the LHCIIb trimer, was substantially reduced, and another LHCIIb trimer component, Lhcb2, was slightly reduced in the gdc1-3 mutant, although their transcription levels were not altered in the mutant. This suggests that defective LHCII trimer formation in gdc1-3 is due to low amounts of Lhcb1 and Lhcb2. GDC1 encodes a chloroplast protein with an ankyrin domain within the carboxyl terminus. It was highly expressed in Arabidopsis green tissues, and its expression was induced by photosignaling pathways. Immunoblot analysis of the GDC1-green fluorescent protein (GFP) fusion protein in 35S::GDC1-GFP transgenic plants with GFP antibody indicates that GDC1 is associated with an approximately 440-kD thylakoid protein complex instead of the LHCII trimer. This shows that GDC1 may play an indirect role in LHCII trimerization during grana formation.
在陆生植物叶绿体中，类囊体基粒在光合作用中发挥多种作用，包括在光照下增加光合作用能力和在遮荫下增强光化学效率。然而，基粒形成的分子机制仍然难以捉摸。在这里，我们报告了一个新的基因，Grana-Deficient Chloroplast1（GDC1），它是拟南芥（Arabidopsis thaliana）叶绿体基粒形成所必需的。在 knockout 突变体 gdc1-3 的叶绿体中，只观察到基质类囊体，它们不能堆叠在一起形成紧密排列的基粒。该突变体表现出幼苗致死性，子叶呈淡绿色，真叶也是如此。进一步的蓝色 native-聚丙烯酰胺凝胶电泳分析表明，gdc1-3 中 hardly 检测到三聚体形式的 Light-Harvesting Complex II（LHCII），证实了之前的报道，即 LHCII 三聚体对于基粒形成是必不可少的。Lhcb1 蛋白是 LHCIIb 三聚体的主要成分，在 gdc1-3 突变体中显著减少，另一个 LHCIIb 三聚体成分 Lhcb2 也略有减少，尽管它们的转录水平在突变体中没有改变。这表明 gdc1-3 中 LHCII 三聚体形成缺陷是由于 Lhcb1 和 Lhcb2 的含量低所致。GDC1 编码一种叶绿体蛋白，其羧基末端具有锚蛋白结构域。它在拟南芥绿色组织中高度表达，其表达受 photosignaling 途径诱导。用 GFP 抗体对 35S::GDC1-GFP 转基因植物中的 GDC1-绿色荧光蛋白（GFP）融合蛋白进行免疫印迹分析表明，GDC1 与大约 440-kD 的类囊体蛋白复合物相关，而不是与 LHCII 三聚体相关。这表明 GDC1 可能在基粒形成过程中 LHCII 三聚体化中发挥间接作用。
