Expression of Bra r 1 gene in transgenic tobacco and Bra r 1 promoter activity in pollen of various plant species

Bra r 1 encodes a Ca2+-binding protein specifically expressed in anthers of Brassica rapa. In this study, we isolated a genomic clone of Bra r I and f ound sequences similar to Pollen Box core motifs and LAT56/59 box, pollen-s pecific cis-acting element, in the 5' upstream region of Bra r 1. Reporter gene fusion revealed that the Bra r 1 promoter directs male gametophytic ex pression in Nicotiana tabacum, Arabidopsis thaliana and B. napus, showing s trong expression in mature pollen grains similar to that of endogenous Bra r 1. Genomic DNA of Bra r 1 was introduced into tobacco plants and the high est accumulation of Bra r 1 protein was observed in mature pollen in the sa me manner as reporter gene expression. Using in vitro-germinated pollen tub es of transgenic tobacco, we firstly demonstrated the subcellular localizat ion of Bra r 1 in pollen tubes. Bra r 1 protein was distributed throughout the pollen tube of transgenic tobacco and slightly intense signals of Bra r 1 were observed in the tip region. In long-germinated pollen tubes, Bra r 1 was detected only in the cytoplasmic compartments while no signals were o bserved in the empty part of the pollen tube, indicating that cytoplasmic m ovement toward the tube tip is accompanied by Bra r 1, Hence, we suggest th at Bra r 1 is involved in pollen germination and pollen tube growth.