Genetic transformation of fruit trees: current status and remaining challenges

Genetic transformation has emerged as a
powerful tool for genetic improvement of fruit trees
hindered by their reproductive biology and their high
levels of heterozygosity. For years, genetic engineering
of fruit trees has focussed principally on enhancing
disease resistance (against viruses, fungi, and bacteria),
although there are few examples of field cultivation and
commercial application of these transgenic plants. In
addition, over the years much work has been performed
to enhance abiotic stress tolerance, to induce modifications
of plant growth and habit, to produce marker-free
transgenic plants and to improve fruit quality by
modification of genes that are crucially important in
the production of specific plant components. Recently,
with the release of several genome sequences, studies of
functional genomics are becoming increasingly important:
by modification (overexpression or silencing) of
genes involved in the production of specific plant
components is possible to uncover regulatory mechanisms
associated with the biosynthesis and catabolism
of metabolites in plants. This review focuses on the
main advances, in recent years, in genetic transformation
of the most important species of fruit trees,
devoting particular attention to functional genomics
approaches and possible future challenges of genetic
engineering for these species in the post-genomic era.