Li Rui-Qing, Jiang Meng, Liu Yan-Hua, Zheng Yun-Chao, Huang Jian-Zhong, Wu Jian-Min, Shu Qing-Yao
National Key Laboratory of Rice Biology, Institute of Crop Sciences, Zhejiang UniversityHangzhou, China.
Hubei Collaborative Innovation Center for Grain IndustryJingzhou, China.
Front Plant Sci. 2017 May 31;8:901. doi: 10.3389/fpls.2017.00901. eCollection 2017.
The marker trait, which is controlled by a down-regulating epi-mutation of , has been applied to the production of hybrid rice. However, the molecular basis for the ability of mutants to attain high photosynthetic capacity even with decreased chlorophyll contents has not been characterized. In the present study, we observed that the total chlorophyll content of the mutant was only 27.2% of that of the wild-type (WT) plants. However, the mutant still accumulated 59.9% of the WT δ-aminolevulinic acid content, 72.8% of the WT Mg-protoporphyrin IX content, and 63.0% of the WT protochlorophyllide content. Additionally, the protoporphyrin IX and heme contents in the mutant increased to 155.0 and 160.0%, respectively, of the WT levels. A search for homologs resulted in the identification of 124 rice genes involved in tetrapyrrole biosynthesis and photosynthesis. With the exception of , , and , the expression levels of the genes involved in tetrapyrrole biosynthesis were significantly higher in the mutant than in the WT plants, as were all 72 photosynthesis-associated nuclear genes. In contrast, there were no differences between the mutant and WT plants regarding the expression of all 22 photosynthesis-associated chloroplast genes. Furthermore, the abundance of O and the expression levels of O-related genes were lower in the mutant than in the WT plants, indicating O-mediated retrograde signaling was repressed in the mutant plants. These results suggested that the abundance of protoporphyrin IX used for chlorophyll synthesis decreased in the mutant, which ultimately decreased the amount of chlorophyll in the mutant. Additionally, the up-regulated expression of photosynthesis-associated nuclear genes enabled the mutant to attain a high photosynthetic capacity. Our findings confirm that OsGUN4 plays an important role in tetrapyrrole biosynthesis and photosynthesis in rice. GUN4, chlorophyll synthesis pathways, and photosynthetic activities are highly conserved in plants and hence, novel traits (e.g., marker trait) may be generated in other cereal crops by modifying the gene.
由一个下调的表观突变所控制的标记性状已应用于杂交水稻的生产。然而，即使叶绿素含量降低，该突变体仍能获得高光能合成能力的分子基础尚未明确。在本研究中，我们观察到该突变体的总叶绿素含量仅为野生型（WT）植株的27.2%。然而，该突变体仍积累了野生型δ-氨基乙酰丙酸含量的59.9%、野生型镁原卟啉IX含量的72.8%以及野生型原叶绿素酸酯含量的63.0%。此外，突变体中原卟啉IX和血红素的含量分别增加到野生型水平的155.0%和160.0%。通过搜索同源物，鉴定出124个参与四吡咯生物合成和光合作用的水稻基因。除了[具体基因名称1]、[具体基因名称2]和[具体基因名称3]外，参与四吡咯生物合成的基因在该突变体中的表达水平显著高于野生型植株，72个与光合作用相关的核基因也是如此。相比之下，22个与光合作用相关的叶绿体基因在突变体和野生型植株中的表达没有差异。此外，该突变体中O[具体物质名称]的丰度和与O[具体物质名称]相关基因的表达水平低于野生型植株，表明该突变体植株中O[具体物质名称]介导的逆行信号受到抑制。这些结果表明，该突变体中用于叶绿素合成的原卟啉IX丰度降低，最终导致该突变体中叶绿素含量减少。此外，与光合作用相关的核基因的上调表达使突变体能够获得高光能合成能力。我们的研究结果证实，OsGUN4在水稻四吡咯生物合成和光合作用中起重要作用。GUN4、叶绿素合成途径和光合活性在植物中高度保守，因此，通过修饰[具体基因名称]，可能在其他谷类作物中产生新的性状（如[具体标记性状名称]）。
