Plant sexual reproduction is a process which depends on the co-ordinate development and activity of the male and female gametophyte. In flowering plants, the male gametophyte or pollen is produced within the anther and its development is dependent on the provision of nutrients and other components from the tissues of the sporophyte as well as on an extensive genetic programme within the pollen grain itself. The analysis of the molecular basis of pollen development and its role in fertilization will improve our understanding of plant reproduction. By differential screening we have isolated a pollen-specific gene ntp303. This gene has been shown to be conserved in dicotyledonous and monocotyledonous species and is transcribed during the late phase of pollen development in the anther and during pollen tube growth in the style. Although the characteristics of the ntp303 gene suggest a function of the protein within the fertilization process, the sequence analysis did not reveal any clues about a possible function. Therefore, we developed a research programme for functional analysis. This research is based on two strategies, the establishment of a functionlocalization relationship and loss of function analysis.