Expression of tandem invertase genes associated with sexual and vegetativegrowth cycles in potato

The organisation of two invertase genes (invGE and invGF) linked in direct tandem repeat within the potato genome is detailed. The genes exhibit a sim ilar intron/exon structure which differs from previously described plant in vertase genes; while intron locations are conserved between the genes, mino r differences in exon length are seen. Both genes encode enzymes with putat ive extracellular location. Biochemical analysis of gene expression showed expression in floral tissues for both genes, with expression of the upstrea m gene (invGE) also detected in leaf tissue. Promoter sequences from both g enes have been fused to the beta-glucuronidase (GUS) reporter gene (uidA) a nd transformed into potato. One promoter-GUS reporter construct was also tr ansformed into tobacco. Histochemical analysis of transgenic lines defined specific expression from the downstream (invGF) promoter in potato and toba cco pollen, with expression first detected in the late uninucleate stage of tobacco microspore development. The invGE promoter determined expression i n pollen and other floral tissues, but also at lateral nodes in stem, root and tuber. An association of invertase expression with generative tissue, b oth in vegetative and sexual modes of growth, is indicated.