Increased stable inheritance of herbicide resistance in transgenic lettucecarrying a petE promoter-bar gene compared with a CaMV 35S-bar gene

Inheritance of resistance to herbicide (300 mg/l glufosinate ammonium) up t o the third (T3) seed generation was compared in two populations of transge nic lettuce (Lactuca sativa L. cv 'Evola') harbouring a T-DNA containing th e bar gene, linked to either the Cauliflower Mosaic Virus (CaMV) 35S promot er, or a -784-bp plastocyanin promoter from pea (petE). Only 2.5% (4/163) o f CaMV 35S-bar plants, selected by their kanamycin resistance (TO generatio n), transmitted herbicide resistance at high frequency to their T3 seed gen eration compared with 97% (29/30) for kanamycin resistant petE-bar plants. In the case of 35S-bar transformants, only 16% (341/2,150) of the first see d generation (T1) plants, 22% (426/1,935) T2 plants and 11% (1,235/10,949) T3 plants were herbicide-resistant, In contrast, 63% (190/300) T1 plants, 8 3% (2,370/2,845) T2 plants and 99% (122/123) T3 petE-bar transformed plants were resistant to glufosinate ammonium. The T-DNAs carrying the petE-bar a nd CaMV 35S-bar genes also contained a CaMV 35S-neomycin phosphotransferase (nptII) gene. ELISA showed that NPTII protein was absent in 29% (45/156) o f the herbicide-resistant T2 plants from 8/19 herbicide-resistant petE-bar lines. This indicated specific inactivation of the CaMV 35S promoter on the same T-DNA locus as an active petE promoter. The choice of promoter and T- DNA construct are crucial for long-term expression of transgenes in lettuce .