Increased activity of MdFRK2, a high-affinity fructokinase, leads to upregulation of sorbitol metabolism and downregulation of sucrose metabolism in apple leaves

Abstract

Sugar metabolism: a master regulator An international study led by Mingjun Li at Northwest A&F University in Shaanxi, China, reveals that an enzyme regulating the utilization of fructose in apple plants, fructokinase 2 (FRK2), has a key role in sugar metabolism. Overexpressing the gene encoding FRK2 in apple plants did not affect their growth or levels of sorbitol, the major product of photosynthesis in these plants, but it significantly lowered the levels of fructose, glucose and sucrose in mature leaves and increased the levels of starch. Accordingly, the activity of enzymes involved in sucrose and glucose metabolism was downregulated, whereas the activity of those involved in sorbitol metabolism was upregulated. Future analysis of the fruit and flowers will shed further light on the role of FRK in controlling sugar levels and the distribution of carbon in apple plants.