拟南芥核糖核酸酶RNJ参与锰在叶绿体中的利用机制研究

Manganese (Mn) is an indispensable micronutrient for plant growth and development, which is the component of photosystem Ⅱ and has an important role in chloroplast photosynthesis. However, the mechanism that how Mn is involved in the other biologic process in chloroplasts is largely unknown. By establishing a nramp1-EMS mutagenesis library, we screened an Arabidopsis mutant mdg3/+ nramp1 that was specifically hypersensitive to Mn deficiency. Under the Mn-deficient conditions, this mutant exhibited yellow newer leaf phenotype, and the chloroplasts were severely defected. Through the whole genome sequencing, we identified that the mutation site localized on the RNJ gene, which encodes a ribonuclease in chloroplast that has been reported to be involved in the RNA processing. Interestingly, our previous results showed that the decreased function of RNJ resulted in the abnormal expression of a series of chloroplast genes under the Mn-deficient conditions, which indicated that Mn might be an activation factor of ribonuclease RNJ and is involved in the process of RNA metabolism. Based on these, firstly we would further investigate the dependence of its function on the manganese. Then we would detect the activity of RNJ regulated by Mn and check the influence of RNJ abundance and activity on the processing of RNA under Mn deficiency. Our work would further clarify the mechanism that the function of RNJ depended on Mn in the chloroplast.

锰是植物必需的矿质营养元素，其作为光系统Ⅱ的组成成分之一，在叶绿体的光合作用中扮演着不可或缺的角色。然而除光合作用外，叶绿体中的锰是否还参与其它的生物学过程尚不清楚。通过筛选以nramp1为背景的突变体库，我们获得了一个对缺锰特异敏感的拟南芥突变体mdg3/+ nramp1。该突变体在缺锰条件下出现明显的新叶黄化，叶绿体片层结构发育不完整。经鉴定该突变基因为编码叶绿体核糖核酸酶的RNJ基因，参与叶绿体RNA前体的加工代谢。有趣的是，在缺锰胁迫时，RNJ的突变影响了一系列叶绿体基因的表达，这提示锰离子可能作为核糖核酸酶的活化因子，参与叶绿体RNA前体的加工。基于此，我们将进一步确证RNJ的功能对锰的依赖性，分析RNJ的活性与锰离子的关系，同时探讨缺锰胁迫下RNJ的丰度及其活性对叶绿体RNA前体加工的影响，以期最终阐明叶绿体核糖核酸酶RNJ利用微量元素锰的分子机制。

锰是植物正常生长不可缺少的微量元素之一。在叶绿体中，锰主要作为放氧复合体的活性中心参与植物的光合作用，然而其在叶绿体中的其他利用机制尚不清楚。通过筛选以nramp1为背景的突变体库，我们获得了对缺锰特异敏感的拟南芥突变体mdg3/+ nramp1及mdg14 nramp1。在缺锰条件下，双突变体表现出明显的新叶黄化，叶绿体片层结构发育不完整。经鉴定突变基因均为编码叶绿体核糖核酸酶的RNJ基因。RNJ的功能特异性地依赖于锰离子，其缺失导致植物在缺锰条件下光系统核心蛋白丰度降低，进而影响光系统复合体的组装。细胞中锰离子水平不影响RNJ基因的转录，而缺锰导致RNJ蛋白的稳定性降低。我们的结果揭示了核糖核酸酶RNJ在叶绿体锰的利用过程中具有重要作用。