Wu Ziming, Zhang Xin, He Bing, Diao Liping, Sheng Shenglan, Wang Jiulin, Guo Xiuping, Su Ning, Wang Lifeng, Jiang Ling, Wang Chunming, Zhai Huqu, Wan Jianmin
National Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing 210095, China.
Plant Physiol. 2007 Sep;145(1):29-40. doi: 10.1104/pp.107.100321. Epub 2007 May 25.
Chlorophyll (Chl) synthase catalyzes esterification of chlorophyllide to complete the last step of Chl biosynthesis. Although the Chl synthases and the corresponding genes from various organisms have been well characterized, Chl synthase mutants have not yet been reported in higher plants. In this study, a rice (Oryza Sativa) Chl-deficient mutant, yellow-green leaf1 (ygl1), was isolated, which showed yellow-green leaves in young plants with decreased Chl synthesis, increased level of tetrapyrrole intermediates, and delayed chloroplast development. Genetic analysis demonstrated that the phenotype of ygl1 was caused by a recessive mutation in a nuclear gene. The ygl1 locus was mapped to chromosome 5 and isolated by map-based cloning. Sequence analysis revealed that it encodes the Chl synthase and its identity was verified by transgenic complementation. A missense mutation was found in a highly conserved residue of YGL1 in the ygl1 mutant, resulting in reduction of the enzymatic activity. YGL1 is constitutively expressed in all tissues, and its expression is not significantly affected in the ygl1 mutant. Interestingly, the mRNA expression of the cab1R gene encoding the Chl a/b-binding protein was severely suppressed in the ygl1 mutant. Moreover, the expression of some nuclear genes associated with Chl biosynthesis or chloroplast development was also affected in ygl1 seedlings. These results indicate that the expression of nuclear genes encoding various chloroplast proteins might be feedback regulated by the level of Chl or Chl precursors.
叶绿素（Chl）合酶催化叶绿素酸酯的酯化反应，从而完成叶绿素生物合成的最后一步。尽管已经对来自各种生物体的叶绿素合酶及其相应基因进行了充分表征，但高等植物中尚未报道过叶绿素合酶突变体。在本研究中，分离出了一种水稻（Oryza Sativa）叶绿素缺乏突变体——黄绿叶片1（ygl1），该突变体在幼苗期表现出叶片黄绿，叶绿素合成减少，四吡咯中间体水平增加，叶绿体发育延迟。遗传分析表明，ygl1的表型是由一个核基因的隐性突变引起的。ygl1基因座被定位到第5号染色体，并通过图位克隆法分离出来。序列分析表明它编码叶绿素合酶，并且通过转基因互补验证了其身份。在ygl1突变体中，YGL1的一个高度保守残基中发现了一个错义突变，导致酶活性降低。YGL1在所有组织中组成型表达，其表达在ygl1突变体中没有受到显著影响。有趣的是，编码叶绿素a/b结合蛋白的cab1R基因的mRNA表达在ygl1突变体中受到严重抑制。此外，一些与叶绿素生物合成或叶绿体发育相关的核基因的表达在ygl1幼苗中也受到影响。这些结果表明，编码各种叶绿体蛋白的核基因的表达可能受到叶绿素或叶绿素前体水平的反馈调节。
