469 Multi-faceted Approaches to Genetic Engineering of Petunia × hybrida for Delayed Leaf Senescence

In an effort to modify and study leaf senescence, we have produced several different transgenic petunia lines with altered leaf senescence phenotypes. Using two promoters from senescence-associated genes (sag12 & sag13) fused to the isopentenyl transferase (IPT) gene, which catalyzes the rate-limiting step of cytokinin production, we have produced transgenic petunia plants with delayed lower leaf senescence. We have observed that apparent “leaky” expression of IPT gives rise to plants with other morphological alterations such as increased branching habit and decreased root formation. Plants with delayed leaf senescence phenotypes were selected and bred to produce progeny that were evaluated in greenhouse experiments. Breeding characteristics, horticultural performance and reproduction of these plants will be discussed in terms of potential commercial benefits and limitations. Using the sag12 promoter to drive expression of the knotted (KN1) gene, we have also been able to engineer petunia plants with delayed lower leaf senescence. Initial progeny evaluations of sag12-KN1 petunias will also be discussed.