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 meristems. After 14 days of incubation on solid Murashige and Skoog (MS) medium 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 solid MS medium and acclimated to the greenhouse. This method was highly efficient in tomato and, particularly, in bell pepper, where plant regeneration is especially difficult. We used these explants to transform tomato with Agrobacterium tumefaciens containing a 35S-GUS-intron binary vector. As shown by GUS expression, 47% of the tomato explants produced transformed meristems, which differentiated into plants that exhibited a low (3%) tetraploidy ratio. Southern blots and analysis of inheritance of the foreign genes indicated that T-DNA was stably integrated into the plant genome. The use of this technique opens new prospects for plant transformation in other dicotyledoneous plants in which genetic engineering has been limited, to date, due to the difficulties in developing an efficient in vitro regeneration system.