Epigenetically Modified Crops: Harvesting the Potential of Exogenous dsRNA for Agriculture

Isoamylases are debranching enzymes found in many plants which hydrolyze (1-6)-alpha-D glucosidic linkages in starch, amylopectin, and dextrins and are thought to be responsible for both starch granule formation (ISA1 and ISA2) and degradation (ISA3). Lipid-modified PEI (lmPEI) was synthesized as a carrier for long double stranded RNA (dsRNA, 250-bp long) which targets the three isoamylase isoforms. The particles were applied to the plant via foliar spray and were differentially effective in suppressing expression of ISA1 and ISA2 in the potato leafs, and ISA3 in the potato tubers. Plant growth and other growth traits were not significantly impaired, and starch levels in the tubers were not affected as well. Interestingly enough, the treated plants had significantly smaller starch granule sizes as well as an increased sucrose content which led to an early sprouting phenotype. We confirm the proposal of previous research that an increased number of small starch granules could be responsible for an accelerated turnover of glucan chains and thus a more rapid synthesis of sucrose, and also propose an additional function of ISA3 related to starch granule sizing.