PAUSED, a putative exportin-t, acts pleiotropically in Arabidopsis development but is dispensable for viability.

Exportin-t was first identified in humans as a protein that mediates the export of tRNAs from the nucleus to the cytoplasm. Mutations in Los1p, the Saccharomyces cerevisiae exportin-t homolog, result in nuclear accumulation of tRNAs. Because no exportin-t mutants have been reported in multicellular organisms, the developmental functions of exportin-t have not been determined. Here, we report the isolation and characterization of two Arabidopsis exportin-t mutants, paused-5 and paused-6. The mutant phenotypes indicate that exportin-t acts pleiotropically in plant development. In particular, paused-5 and paused-6 result in delayed leaf formation during vegetative development. The two paused mutations also cause the transformation of reproductive organs into perianth organs in the hua1-1 hua2-1 background, which is partially defective in reproductive organ identity specification. The floral phenotypes of hua1-1 hua2-1 paused mutants resemble those of mutations in the floral homeotic gene AGAMOUS. Moreover, paused-5 enhances the mutant phenotypes of two floral meristem identity genes, LEAFY and APETALA1. The developmental defects caused by paused mutations confirm the important roles of exportin-t in gene expression in multicellular organisms. In addition, a paused null allele, paused-6, is still viable, suggesting the presence of redundant tRNA export pathway(s) in Arabidopsis.

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