DIFFERENTIAL EXPRESSION OF THE 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASE GENE FAMILY OF TOMATO

The tomato ACC oxidase gene family is comprised of three members desig nated ACO1, ACO2 and ACO3. These are highly homologous throughout the protein coding regions but do show a degree of sequence divergence wit hin the 3' untranslated regions. These regions have been cloned and us ed as gene-specific probes to analyse the differential expression of t he tomato ACC oxidase gene family in various tissues at different stag es of development. Results indicate that all three genes are transcrip tionally active and display a high degree of inducibility in a number of organs at various stages of the life cycle. Both ACO1 and ACO3 tran scripts accumulate during the senescence of leaves, fruit and flowers. In addition, it appears that ACO1 is wound-inducible in leaves. All t hree ACC oxidase genes are expressed during flower development, with e ach showing a temporally distinct pattern of accumulation. In addition , the ACC oxidase transcripts are also spatially regulated throughout flower development; ACO1 is predominantly expressed in the petals and the stigma and style, ACO2 expression is mainly restricted to tissues associated with the anther cone whereas ACO3 transcripts accumulate in all of the floral organs examined apart from the sepals. ACC oxidase enzyme assays and Western blot analysis indicate that both enzyme acti vity and ACC oxidase protein increase with transcript abundance in sev eral tissues. The physiological role of the differential expression of the ACC oxidase gene family, in relation to the regulation of ethylen e synthesis, during these various developmental processes is discussed .