An active RNA transport mechanism into plant vacuoles

Abstract

RNA degradation inside the plant vacuole by the ribonuclease RNS2 is essential for maintaining nucleotide concentrations and cellular homeostasis via the nucleotide salvage pathway. However, the mechanisms by which RNA is transported into the vacuole are not well understood. While selective macroautophagy may contribute to this transport, macroautophagy-independent transport pathways also exist. Here we demonstrate a mechanism for direct RNA transport into vacuoles that is active in purified vacuoles and is ATP hydrolysis-dependent. We identify the RNA helicase SKI2 as a factor required for this transport pathway, as ski2 mutant vacuoles are defective in transport. ski2 mutants have an increased autophagy phenotype that can be rescued by exogenous addition of nucleosides, consistent with a function in nucleotide salvage. This newly-described transport mechanism is therefore critical for RNA degradation, recycling and cytoplasmic nucleotide homeostasis.

RNA biology takes root in plant systems

“…Both double null mutants atg5-1 rns2-2 and atg9-4 rns2-2 eliminate constitutive autophagy found in rns2-2, but only atg5-1 rns2-2 arrests vacuolar rRNA transport suggesting the importance of autophagy, especially ATG5, in selective ribosome turnover (Floyd et al, 2015). Dr. MacIntosh's group subsequently found, through use of a fluorescent RNA assay and a null mutant of RNA exosome-associated DExD/H box RNA helicase SUPERKILLER2 (AtSKI2), that ski2-5 null mutant plants have reduced ability to transport fluorescent RNA to vacuoles (Floyd et al, 2022). Global DNA methylation patterning has emerged as a critical layer of genetic regulation with the establishment, removal, and regulation of these marks indicative of a complex and highly regulated evolved mechanism in Arabidopsis and other eukaryotes (Bartels et al, 2018;Law & Jacobsen, 2010).…”