Floyd Brice E, Mugume Yosia, Morriss Stephanie C, MacIntosh Gustavo C, Bassham Diane C
Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA, 50011, USA.
Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA, 50011, USA.
Planta. 2017 Apr;245(4):779-792. doi: 10.1007/s00425-016-2644-x. Epub 2016 Dec 26.
Localization of the RNase RNS2 to the vacuole via a C-terminal targeting signal is essential for its function in rRNA degradation and homeostasis. RNase T2 ribonucleases are highly conserved enzymes present in the genomes of nearly all eukaryotes and many microorganisms. Their constitutive expression in different tissues and cell types of many organisms suggests a housekeeping role in RNA homeostasis. The Arabidopsis thaliana class II RNase T2, RNS2, is encoded by a single gene and functions in rRNA degradation. Loss of RNS2 results in RNA accumulation and constitutive activation of autophagy, possibly as a compensatory mechanism. While the majority of RNase T2 enzymes is secreted, RNS2 is located within the vacuole and in the endoplasmic reticulum (ER), possibly within ER bodies. As RNS2 has a neutral pH optimum, and the endomembrane organelles are connected by vesicle transport, the site within the endomembrane system at which RNS2 functions is unclear. Here we demonstrate that localization to the vacuole is essential for the physiological function of RNS2. A mutant allele of RNS2, rns2-1, results in production of an active RNS2 RNase but with a mutation that removes a putative C-terminal vacuolar targeting signal. The mutant protein is, therefore, secreted from the cell. This results in a constitutive autophagy phenotype similar to that observed in rns2 null mutants. These findings illustrate that the intracellular retention of RNS2 and localization within the vacuole are critical for its cellular function.
核糖核酸酶RNS2通过C端靶向信号定位于液泡对于其在rRNA降解和内稳态中的功能至关重要。核糖核酸酶T2核糖核酸酶是几乎所有真核生物和许多微生物基因组中高度保守的酶。它们在许多生物体的不同组织和细胞类型中的组成型表达表明在RNA内稳态中起管家作用。拟南芥II类核糖核酸酶T2，RNS2，由单个基因编码并在rRNA降解中起作用。RNS2的缺失导致RNA积累和自噬的组成型激活，这可能是一种补偿机制。虽然大多数核糖核酸酶T2酶是分泌型的，但RNS2位于液泡和内质网（ER）内，可能在内质网体中。由于RNS2具有中性pH最佳值，并且内膜细胞器通过囊泡运输相连，因此RNS2在内膜系统中发挥作用的位点尚不清楚。在这里，我们证明定位于液泡对于RNS2的生理功能至关重要。RNS2的一个突变等位基因rns2-1导致产生一种活性RNS2核糖核酸酶，但带有一个突变，该突变去除了一个假定的C端液泡靶向信号。因此，突变蛋白从细胞中分泌出来。这导致了一种与rns2缺失突变体中观察到的相似的组成型自噬表型。这些发现表明，RNS2在细胞内的保留和在液泡内的定位对其细胞功能至关重要。
