Expression and subcellular localization of pre-rRNA processing factor homologues in higher plants

Rpf2 (Ribosome Production Factor 2) is involved in ribosome biogenesis, and functions as one of the pre-rRNA processing factors. Although properties of the Rpf2 protein in yeast have been described in detail, there have been no reports on Rpf2 homologues in higher eukaryotes. To investigate the function of Rpf2 homologues in higher plants, we identified genes encoding Rpf2-like proteins from Arabidopsis and rice and designated them AtRpf2 and OsRpf2, respectively. The predicted amino acid sequence revealed that both genes contain the Brix domain, a characteristic domain associated with ribosome biogenesis, and a sigma 70-like RNA binding motif, a eukaryotic RNA binding domain unique to a superfamily of proteins required for ribosome biogenesis. Both gene transcripts were detected in all organs and tissues tested and the expression patterns were consistent with the typical expression pattern of previously described ribosomal protein genes. Transient expression of GFP::AtRpf2 and GFP::OsRpf2 revealed predominant nucleolar localization within the nucleus of both fusion proteins in onion epidermal cells and tobacco BY-2 cells. These results suggest that Rpf2-like proteins in higher plants are also involved in ribosome biogenesis and function as pre-rRNA processing factors.