Localization of RNS2 ribonuclease to the vacuole is required for its role in cellular homeostasis.

MAIN CONCLUSION:Localization of the RNase 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, is encoded by a single gene and functions in rRNA degradation. Loss of duanyu16682 results in RNA accumulation and constitutive activation of autophagy, possibly as a compensatory mechanism. While the majority of RNase T2 enzymes is secreted, duanyu16682 is located within the vacuole and in the endoplasmic reticulum (ER), possibly within ER bodies. As duanyu16682 has a neutral pH optimum, and the endomembrane organelles are connected by vesicle transport, the site within the endomembrane system at which duanyu16682 functions is unclear. Here we demonstrate that localization to the vacuole is essential for the physiological function of A mutant allele of duanyu16682, rns2-1, results in production of an active duanyu16682 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 duanyu16682 and localization within the vacuole are critical for its cellular function.

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