Department of Applied Biology, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 61186, South Korea.
Faculty of Forestry Agriculture, Tay Nguyen University, Buon Ma Thuot, Daklak 63000, Vietnam.
Plant Cell Physiol. 2021 Oct 11;62(6):948-958. doi: 10.1093/pcp/pcab060.
Ribosomal RNA (rRNA) methylation is a pivotal process in the assembly and activity of ribosomes, which in turn play vital roles in the growth, development and stress responses of plants. Although few methyltransferases responsible for rRNA methylation have been identified in plant chloroplasts, the nature and function of these enzymes in chloroplasts remain largely unknown. In this study, we characterized ArabidopsisRsmD (At3g28460), an ortholog of the methyltransferase responsible for N2-methylguanosine (m2G) modification of 16S rRNA in Escherichia coli. Confocal microscopic analysis of an RsmD- green fluorescent protein fusion protein revealed that RsmD is localized to chloroplasts. Primer extension analysis indicated that RsmD is responsible for m2G methylation at position 915 in the 16S rRNA of Arabidopsis chloroplasts. Under cold stress, rsmd mutant plants exhibited retarded growth, i.e. had shorter roots, lower fresh weight and pale-green leaves, compared with wild-type (WT) plants. However, these phenotypes were not detected in response to drought or salt stress. Notably, the rsmd mutant was hypersensitive to erythromycin or lincomycin and accumulated fewer chloroplast proteins compared with the WT, suggesting that RsmD influences translation in chloroplasts. Complementation lines expressing RsmD in the rsmd mutant background recovered WT phenotypes. Importantly, RsmD harbored RNA methyltransferase activity. Collectively, the findings of this study indicate that RsmD is a chloroplast 16S rRNA methyltransferase responsible for m2G915 modification that plays a role in the adaptation of Arabidopsisto cold stress.
核糖体 RNA（rRNA）甲基化是核糖体组装和活性的关键过程，而核糖体在植物的生长、发育和应激反应中起着至关重要的作用。尽管已经在植物叶绿体中鉴定出了少数负责 rRNA 甲基化的甲基转移酶，但这些酶在叶绿体中的性质和功能在很大程度上仍然未知。在这项研究中，我们对拟南芥 RsmD（At3g28460）进行了表征，它是大肠杆菌中负责 16S rRNA N2-甲基鸟苷（m2G）修饰的甲基转移酶的同源物。RsmD-绿色荧光蛋白融合蛋白的共焦显微镜分析表明，RsmD定位于叶绿体。引物延伸分析表明，RsmD负责拟南芥叶绿体 16S rRNA 中 m2G 修饰位置 915。在冷胁迫下，与野生型（WT）植物相比，rsmd 突变体植物的生长受到抑制，即根较短，鲜重较低，叶片呈淡绿色。然而，在干旱或盐胁迫下没有检测到这些表型。值得注意的是，与 WT 相比，rsmd 突变体对红霉素或林可霉素敏感，并且积累的叶绿体蛋白较少，这表明 RsmD 影响叶绿体中的翻译。在 rsmd 突变体背景下表达 RsmD 的互补系恢复了 WT 表型。重要的是，RsmD 具有 RNA 甲基转移酶活性。总之，这项研究的结果表明，RsmD 是一种负责 m2G915 修饰的叶绿体 16S rRNA 甲基转移酶，它在拟南芥适应冷胁迫中发挥作用。
