Recent results from transformation of apple

Production of intragenic disease resistant lines of preferred apple cultivars by makerless transformation has been hampered by chimerism.  Use of the myb10 transcription factor has provided insight into origin of chimeric and uniformly transformed shoots.  Over-expression of the apple transcription facilitator gene, MpNPR1, provides a commercially useful level of resistant to the bacterial disease, fire blight (FB).  Use of additional genes for resistance to FB is desirable to increase durability of resistance. RNAi-silencing constructs of candidate resistance genes were created using ESTs associated with response of apple to E. amylovora that were selected based upon transcript profiling data and bioinformatics. Phenotyping of RNAi-silenced mutants following inoculation of young plants with E. amylovora indicated effect of some genes on disease progress. With the aim of developing an ornamental apple with polypetalous flowers, an RNAi phenotype of Galaxy (GX) apple was successfully expressed after six years growth in the greenhouse. The C- Class gene function was partially altered, with variable phenotype among lines.  All the stamens were converted into petals; the shape of locules was irregular; and there was a variable number of ovules per carpel. The number of petals in the RNAi GX flowers was 20-25 vs. 5 in GX.  These results add to our understanding of regulation of floral development in apple, and may lead to development of polypetalous sterile ornamental apple cultivars.