Instituto de Bioingeniería, Universidad Miguel Hernández, Campus de Elche, 03202 Elche, Alicante, Spain.
Centre National de la Recherche Scientifique, Laboratoire Génome et Développement des Plantes, Unité Mixte de Recherche 5096, 66860 Perpignan, France.
Plant Physiol. 2020 Dec;184(4):2022-2039. doi: 10.1104/pp.19.01540. Epub 2020 Sep 10.
Ribosome biogenesis is crucial for cellular metabolism and has important implications for disease and aging. Human () glioma tumor-suppressor candidate region gene2 (GLTSCR2) and yeast () Nucleolar protein53 (Nop53) are orthologous proteins with demonstrated roles as ribosome biogenesis factors; knockdown of GLTSCR2 impairs maturation of 18S and 5.8S ribosomal RNAs (rRNAs), and Nop53 is required for maturation of 5.8S and 25S rRNAs. Here, we characterized SMALL ORGAN4 (SMO4), the most likely ortholog of human GLTSCR2 and yeast Nop53 in Arabidopsis (). Loss of function of SMO4 results in a mild morphological phenotype; however, we found that mutants exhibit strong cytological and molecular phenotypes: nucleolar hypertrophy and disorganization, overaccumulation of 5.8S and 18S rRNA precursors, and an imbalanced 40S:60S ribosome subunit ratio. Like yeast Nop53 and human GLTSCR2, Arabidopsis SMO4 participates in 5.8S rRNA maturation. In yeast, Nop53 cooperates with mRNA transport4 (Mtr4) for 5.8S rRNA maturation. In Arabidopsis, we found that SMO4 plays similar roles in the 5.8S rRNA maturation pathway than those described for MTR4. However, SMO4 seems not to participate in the degradation of by-products derived from the 5'-external transcribed spacer (ETS) of 45S pre-rRNA, as MTR4 does.
核糖体生物发生对于细胞代谢至关重要，并且对疾病和衰老具有重要意义。人类（）神经胶质瘤肿瘤抑制候选区基因 2（GLTSCR2）和酵母（）核仁蛋白 53（Nop53）是具有核糖体生物发生因子作用的同源蛋白；GLTSCR2 的敲低会损害 18S 和 5.8S 核糖体 RNA（rRNA）的成熟，而 Nop53 是 5.8S 和 25S rRNA 成熟所必需的。在这里，我们对 SMALL ORGAN4（SMO4）进行了描述，SMO4 是拟南芥（）中人类 GLTSCR2 和酵母 Nop53 的最可能同源物。SMO4 功能丧失导致轻微的形态表型；然而，我们发现（）突变体表现出强烈的细胞学和分子表型：核仁肥大和紊乱，5.8S 和 18S rRNA 前体过度积累，以及 40S：60S 核糖体亚基比例失衡。与酵母 Nop53 和人类 GLTSCR2 一样，拟南芥 SMO4 参与 5.8S rRNA 成熟。在酵母中，Nop53 与 mRNA 转运 4（Mtr4）合作进行 5.8S rRNA 成熟。在拟南芥中，我们发现 SMO4 在 5.8S rRNA 成熟途径中发挥的作用与 MTR4 类似。然而，SMO4 似乎不参与由 45S 前 rRNA 5'-外部转录间隔区（ETS）衍生的副产物的降解，而 MTR4 则参与。
