镁离子螯合酶是叶绿素合成过程中的关键酶之一,与植物叶色的白化现象密切相关。以陕茶1号、白叶1号、极白1号、黄金芽和黄金叶等5个茶树品种叶片为试验材料,分别克隆其镁离子螯合酶I亚基（Mg-chelatase I subunit,CHLI）编码基因CsCHLI全长CDS序列。多序列比对显示,白叶1号中两个碱基差异位点（G502C,C1169T）导致在AAA+和AAA lid结构域中有2个氨基酸残基发生改变（G168R,A390V）,黄金叶中1个碱基差异位点（G1202A）导致在AAA lid结构域中有1个氨基酸残基发生改变（R401H）。亚细胞定位结果显示,CsCHLI定位于叶绿体中,碱基或氨基酸残基的差异并不影响其亚细胞定位。RNA二级结构分析表明,碱基位点突变会影响CsCHLI的茎环结构和二级结构的稳定性。与陕茶1号相比,不同叶色白化茶树品种中总叶绿素含量分别为陕茶1号的25%~77%,CsCHLI基因表达量分别为陕茶1号的24%~46%。结果表明,茶树中CsCHLI的基因表达与叶绿素含量呈正相关。这些结果将为深入研究CsCHLI在茶树叶绿素代谢中的功能以及茶树叶色突变的作用机理提供试验证据。
Magnesium chelatase is one of the key enzymes in the process of chlorophyll synthesis, which is closely related to the albino phenomenon of leaves. In this study, the leaves of tea cultivars Shaancha 1, Baiye 1, Jibai 1, Huangjinya and Haungjinye were used as materials to clone the full-length CDS sequences of CsCHLI (Mg-chelatase I subunit). Multi-sequence alignment shows that the two base differences (G502C, C1169T) were found in Baiye 1, which lead to the change of two amino acid residues (G168R, A390V) in the AAA+ and AAA lid domain. Meanwhile, there was an amino acid residue changed (R401H) in the AAA lid domain of Huangjinye, due to the difference of G1202A. Subcellular localization analyses illustrates that CsCHLI is localized in chloroplast and the differences of the bases or amino acid residues did not affect its subcellular localization. The RNA secondary structure analysis shows that base site mutations of CsCHLI would affect its stem-loop structure and the stability. Moreover, the chlorophyll contents in albino tea plants were 25%-77% of that in Shaancha 1, and the expressions of CsCHLI in albino tea plants were 24%-46% of that in Shaancha 1. The results show that the CsCHLI expression was positively correlated with chlorophyll content in tea plants. Furthermore, these results provided experimental evidences for the in-depth study of the chlorophyll metabolism in albino tea plants.
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