Transgenic peach plants (Prunus persica L.) produced by genetic transformation of embryo sections using the green fluorescent protein (GFP) as an in vivo marker

The main obstacle to genetic engineering of fruit tree species is the regeneration of transformed plantlets. Transformation events in peach (Prunus persica L.) have been reported using particle bombardment or Agrobacteriummediated transformation of immature embryos. However, the regeneration of plants from transgenic tissues is still difficult and the recovery of non-chimeric plants has not been reported to date. In this paper we describe an efficient, reliable transformation and regeneration system to produce transgenic peach plants using embryo sections of mature seeds as starting material. This represents an important advantage due to the availability of such material throughout the year. A. tumefaciens strain C58 (pMP90) containing the binary plasmid pBin19 was used as vector system for transformation. We used the Nospro-nptII-Noster cassette as a selectable marker and the CaMV35Spro-sgfp-CaMV35Ster cassette as a vital reporter gene coding for an improved version of the green fluorescent protein (sGFP). In vitro cultured embryo sections were Agrobacterium-cocultivated and, after selection, transgenic shoots were regenerated. Shoots that survived exhibited high-level of sGFP expression mainly visible in the young leaves of the apex. In vivo monitoring of GFP expression permitted an early, rapid and easy discrimination of both transgenic and escape buds. After elimination of escapes, transgenic shoots were rooted in vitro and the recovered plantlets were screened using PCR amplification. Southern analysis confirmed stable genomic integration of the sgfp transgene. The high levels of GFP expression were also maintained in the second generation of transgenic peach plants.