Importin ß1 interacts with nuclear transport factors and mediates the import of nuclear proteins. We isolated a pollen-expressed gene, rice Importin ß1 (OsImp ß1), from a T-DNA insertional population that was trapped by a promoterless ß-glucuronidase (GUS) gene. The GUS reporter was expressed in the anthers and ovaries from early through mature developmental stages. Its expression was also observed in all floral organs. However, these patterns changed as the spikelet developed. T-DNA was inserted into the OsImp ß1 gene at 339 bp downstream from the translation initiation site. We obtained another T-DNA insertional allele by searching the flanking sequence tag database. In both lines, the wild-type and T-DNA-carrying progeny segregated at a ratio close to 1:1. The latter genotype was heterozygous (OsImp ß1/osimp ß1). Reciprocal crosses between WT and heterozygous plants demon-strated that the mutant alleles could not be transmitted through the male gametophyte. Close examination of the heterozygous anthers revealed that the mutant pollen matured normally. However, in vitro assays showed that tube elongation was hampered in the mutant grains. These results indicate that OsImp ß1 is specifically required for pollen tube elongation.

Keywords: GUS, importin