The Nuclear Pore Protein AtTPR Is Required for RNA Homeostasis, Flowering Time, and Auxin Signaling

Nuclear pore complexes (NPCs) mediate the transport of RNA and other cargo between the nucleus and the cytoplasm. In vertebrates, the NPC protein TRANSLOCATED PROMOTER REGION (TPR) is associated with the inner filaments of the nuclear basket and is thought to serve as a scaffold for the assembly of transport machinery. In a screen for mutants that suppress the expression of the floral inhibitor FLOWERING LOCUS C, we identified lesions in the Arabidopsis (Arabidopsis thaliana) homolog of TPR (AtTPR). attpr mutants exhibit early-flowering and other pleiotropic phenotypes. A possible explanation for these developmental defects is that attpr mutants exhibit an approximately 8-fold increase in nuclear polyA RNA. Thus AtTPR is required for the efficient export of RNA from the nucleus. Microarray analysis shows that, in wild type, transcript abundance in the nuclear and total RNA pools are highly correlated; whereas, in attpr mutants, a significantly larger fraction of transcripts is enriched in either the nuclear or total pool. Thus AtTPR is required for homeostasis between nuclear and cytoplasmic RNA. We also show that the effects of AtTPR on small RNA abundance and auxin signaling are similar to that of two other NPC-associated proteins, HASTY (HST) and SUPPRESSOR OF AUXIN RESISTANCE3 (SAR3). This suggests that AtTPR, HST, and SAR3 may play related roles in the function of the nuclear pore.