Engineering the Apple Fruit As the Ultimate Functional Food and Nutraceutical Factory

Throughout many parts of the world, the cultivated apple is synonymous with nutrition and health. Unlike many fruits, the apple can be tough enough to withstand the physical demands of shipping, and resilient to long periods of storage. The fruit can be easily processed, and a vast amount of infrastructure exists to support juice and concentrate production. A multitude of species, cultivars and hybrids exist with diverse fruit biochemistry. These qualities make apple an attractive and versatile vehicle for the production and delivery of phytoceutical and nutraceutical compounds, both by harnessing the biochemical diversity that already exists, and by engineering novel exogenous compounds through biotechnology. As an example, we characterized > 100 apple variant genotypes that produce anthocyanins in the fruit cortex (flesh) as well as the skin. In nearly all these genotypes, this trait is driven by a previously identified, gain-of-function mutation in a transcription factor driving the anthocyanin biochemical pathway. However, the activity of this mutation is strongly subject to modification by gene(s)/allele(s) that remain to be identified. We propose that novel cultivars could easily be engineered that produce very high levels of anthocyanins in the fruit for nutraceutical use. Toward the goal of using biotechnology to drive production of exogenous compounds in apple, we used transcriptional profiling to characterize gene expression throughout the full range of fruit development in a wild apple species. We identified genetic elements associated with specific expression patterns, which can now be exploited to drive biosynthesis in a developmentally authentic manner.