Novel Functions of Arabidopsis Pumilio RNA-Binding Protein 6 in Salt Stress

To control gene expression, plants use the post-transcriptional/translational regulation system, which plays important roles in development and biotic and abiotic responses. Some RNAbinding proteins (RBPs) are known to regulate target genes via direct binding of specific RNA motifs. Pumilio and fem-3 binding factor (Puf) proteins exhibit a specific capacity for binding of the 3' untranslational region (3' UTR) of target mRNA and work as a post-transcriptional regulator in the mammalian system. Recently, it was reported that Arabidopsis Pumilio RNA-binding protein (APUM), a plant Puf homologue, is involved in biotic and abiotic stress and development. However, the function of plant Puf proteins has not yet been fully recovered. In the current study, APUM6 gene expression was reduced by salt stress. APUM6 localized in the cytoplasmic foci of the mRNA decay sites and ER membrane. Purified APUM6-pumilio homologue domain (HD) protein showed 'UGUANAUA' binding activity in vitro. APUM6-RNAi transgenic plants displayed reduced tolerance to salt stress during the germination and mature plant stages. In AP UM6-RNAi transgenic plants under salt stress, abiotic stress-responsive gene expression levels showed no significant difference compared with Col-0. Collectively, these results indicate that APUM6 might play important roles in responses to salt stress via translational modification.