A beta-galactosidase-like gene is expressed during tobacco pollen development

cDNA clone (TP5) with significant homology to ss-galactosidases has been isolated from a mature tobacco pollen cDNA library by differential screening. The predicted protein of 715 aa shows high levels of homology to plant beta-galactosidases expressed during fruit ripening and senescence. Northern analysis shows that the TP5 transcript is expressed exclusively in developing anthers and mature pollen. The transcript is present at very low levels at meiosis and increases dramatically, late in microspore development after mitosis suggesting that the primary role for the protein is during pollen tube growth. beta-galactosidase activity, measured by scanning densitometry of histochemically stained tobacco microspores, is first detectable in the early to mid-vacuolate stage, and reaches a peak at microspore mitosis, thereafter decreasing as the microspores reach maturity. Southern analysis indicates that the TP5 gene is present in two copies, probably corresponding to the two ancestral genomes of N. tabacum.