Pumilio Puf domain RNA-binding proteins in Arabidopsis

Abstract

Pumilio proteins are a class of RNA-binding proteins harboring Puf domains (or PUM-HD; Pumilio-Homology Domain), named after the founding members, Pumilio (from Drosophila melanogaster) and FBF (Fem-3 mRNA-Binding Factor from Caenorhabditis elegans). The domains contain multiple tandem repeats each of which recognizes one RNA base and is comprised of 35-39 amino acids. Puf domain proteins have been reported in organisms ranging from single-celled yeast to higher multicellular eukaryotes, such as humans and plants. In yeast and animals, they are involved in a variety of posttranscriptional RNA metabolism including RNA decay, RNA transport, rRNA processing and translational repression. However, their roles in plants are largely unknown. Recently, we have characterized the first member of the Puf family of RNA-binding proteins, APUM23, in Arabidopsis. Here, we discuss and summarize the diverse roles and targets of Puf proteins previously reported in other organisms and then highlight the potential regulatory roles of Puf proteins in Arabidopsis, using our recent study as an example.

Figure 1

Histochemical GUS staining in the transgenic plants expressing β-glucuronidase gene under the control of APUM gene promoters.

Figure 2

Possible nucleolar functions of APUM23. APUM23 is required for rRNA processing (1) and affects ribosome biogenesis (2). Because APUM23 is a nucleolar protein, it is possible that it has also other nucleolar functions such as rRNA byproduct degradation by exosome (3), a direct role in translation (4) or an indirect role via its role in ribosome biogenesis (5). Further, auxin and ribosome biogenesis are linked with each other such that defective ribosomes inhibit auxin biosynthesis– (6) and a local auxin accumulation can translationally repress ribosomal genes (7).