Reduced Expression of , Encoding a Novel rRNA Processing Factor, Induces Sugar-Dependent Nucleolar Stress and Altered Sugar Responses in .

Ribosome biogenesis is one of the most energy-consuming events in the cell and must therefore be coordinated with changes in cellular energy status. Here, we show that the sugar-inducible gene () encodes a Pumilio homology domain-containing protein involved in pre-rRNA processing in Null mutation of resulted in aborted embryos due to abnormal gametogenesis and embryogenesis, whereas reduced expression of caused several phenotypes characteristic of ribosome biogenesis or function-related mutants. APUM24 interacted with other pre-rRNA processing factors and a putative endonuclease for the removal of the internal transcribed spacer 2 (ITS2) of pre-rRNA in the nucleolus. The APUM24-containing complex also interacted with ITS2, and reduced expression caused the overaccumulation of processing intermediates containing ITS2. Thus, APUM24 likely functions as an ITS2 removal-associated factor. Most importantly, the knockdown mutant was hypersensitive to highly concentrated sugar, and the mutant showed sugar-dependent overaccumulation of processing intermediates and nucleolar stress (changes in nucleolar size). Furthermore, reduced expression diminished sugar-induced promotion of leaf and root growth. Hence, a breakdown in the coordinated expression of ribosome biogenesis-related genes with energy status may induce nucleolar stress and disturb proper sugar responses in Arabidopsis.