Apple dwarfing rootstocks exhibit an imbalance in carbohydrate allocation and reduced cell growth and metabolism

Dwarfing rootstocks used to grow smaller apple trees have a gene expression profile consistent with reduced cellular activity. Toshi Foster and colleagues from the New Zealand Institute for Plant & Food Research compared gene expression levels between two dwarfing rootstocks (the part of the plant onto which buds or shoots are grafted) and one full-size rootstock. They found that, compared to the full-size rootstock, both the dwarfing rootstocks showed reduced expression of genes involved in metabolism, hormone signaling and cell wall synthesis, and an increased expression of genes involved in breaking down amino acids, lipids and other compounds involved in cellular metabolism. Genes involved in starch synthesis were more active though, suggesting that dwarfing rootstocks keep apple trees small because they are in a continuous state of low energy usage despite having large starch reserves.