Enhanced regeneration of tomato and pepper seedling explants for Agrobacterium-mediated transformation

Seedling explants of three tomato ( Lycopersicon esculentum) and four bell pepper (Capsicum annuum) cultivars consisting of the radicle, the hypocotyl and one cotyledon were obtained after removing the primary and axillary me ristems. After 14 days of incubation on solid Murashige and Skoog (MS) medi um without growth regulators, explants of both species regenerated multiple shoots on the cut surface (2.9-5.3 shoots per explant for tomato and 1.2-2 .2 for bell pepper cultivars). After excision, the shoots were rooted on so lid MS medium and acclimated to the greenhouse. This method was highly effi cient in tomato and, particularly, in bell pepper, where plant regeneration is especially difficult. We used these explants to transform tomato with A grobacterium tumefaciens containing a 35S-GUS-intron binary vector. As show n by GUS expression, 47% of the tomato explants produced transformed merist ems, which differentiated into plants that exhibited a low (3%) tetraploidy ratio. Southern blots and analysis of inheritance of the foreign genes ind icated that T-DNA was stably integrated into the plant genome. The use of t his technique opens new prospects for plant transformation in other dicotyl edoneous plants in which genetic engineering has been limited, to date, due to the difficulties in developing an efficient in vitro regeneration syste m.