The role of sugar signaling in the rescue of a putative Arabidopsis starch-branching enzyme mutant. Methods for the identification of homozygous fructose insensitive mutants from a double mutant F2 population.

Starch is of great importance both for the human diet and for industrial purposes. In order to further direct synthesis of particular starch structures, it is important to understand the role of specific enzymes in starch synthesis. One category of such enzymes are starch branching enzymes, or SBEs, which convert a single chain of glucose into a branched polymer. A putative SBE gene, BE1, has been discovered and studied in Arabidopsis thaliana, for which plants with a weak—that is, non-lethal—mutation, be1-3, have stunted growth and other abnormal phenotypic traits. This phenotype can be partially rescued by addition of metabolizable sugar into the plants’ growth medium, potentially lending credence to BE1 having a role in starch production, as an increase of available metabolite could compensate for the plants’ decreased starch storage abilities. However, as sugar functions not only as a metabolite but also as a signal for certain growth pathways in plants, we seek to study whether this rescue is still observed when sugar signaling capabilities are knocked out through the creation of double mutants for be1-3 and either glucose or fructose insensitive mutations. To further our ability to select these double mutants from the F2 population, we here describe the development of a method to identify plants homozygous for one fructose insensitive gene, FSQ6, using Cleaved Amplified Polymorphic Sequences (CAPS)