A rice DEAD-box RNA helicase protein, OsRH17, suppresses 16S ribosomal RNA maturation in Escherichia coli

DEAD-box proteins comprise a large protein family. These proteins function in all types of processes in RNA metabolism and are highly conserved among eukaryotes. However, the precise functions of DEAD-box proteins in rice physiology and development remain unclear. In this study, we identified a rice DEAD-box protein, OsRH17, that contains a DEAD domain and all of the common conserved motifs of DEAD-box RNA helicases. OsRH17 was specifically expressed in pollen and differentiated callus and upregulated by application of the plant hormones naphthyl acetic acid (NAA) and abscisic acid (ABA). The OsRH17:GFP fusion protein was localized to the nucleus. Tiny amounts of OsRH17 and partial fragments (N-427 and C-167) were detected when they were expressed in Escherichia coli, a prokaryote. Growth of the host cells was suppressed in E. coli by OsRH17, N-427 or C-167, and this suppression was independent of the concentration of the NaCl in the medium. Expression analysis of rRNAs in E. coli revealed that the 16S rRNA precursor accumulated in transgenic E. coli cells, and the relative growth rate was inversely proportional to the levels of pre-16S rRNA accumulation. Results suggested that OsRH17 may play a role in ribosomal biogenesis and suppress 16S rRNA maturation in E. coli. No visible phenotype was observed in transgenic yeast and rice (overexpressing OsRH17, N-427, and C-167, as well as OsRH17 knockdown), and even in some abiotic and biotic stresses, which could be due to the redundancy in rice under normal conditions.