Understanding and modifying starch metabolism to limit yield losses in field-grown cassava

The carbohydrate-rich storage roots of cassava (Manihot esculenta) are among the world's most vital staple foods, providing food security and income for hundreds of millions of people-primarily smallholder farmers in tropical and subtropical regions. Cassava is also a major source of starch for both food and industrial applications. Root yield is largely determined by starch content, which acts as the main sink for photoassimilates during vegetative growth. In addition, stored starch serves as a carbohydrate reservoir that supports regrowth after stress events, such as drought or shoot pruning, or during stem propagation. To investigate source-sink dynamics and identify key factors in sink metabolism, transcriptomic and proteomic analyses of cassava storage roots were conducted following shoot pruning. This perturbation led to a significant reduction in root starch content and triggered widespread transcriptional reprogramming, restricting respiration and growth. Notably, key starch biosynthesis genes were repressed, while starch degradation genes-including the plastidial α-AMYLASE3 A (AMY3A)-were induced. To confirm the role of AMY3 in root starch breakdown, AMY3A-suppressed cassava lines were generated via RNA interference and evaluated under both greenhouse and field conditions. These lines exhibited up to a 7.5-fold reduction in starch mobilization following pruning compared to controls, demonstrating AMY3's key function in storage root starch degradation-a role that contrasts with its redundancy in systems like transitory starch degradation in Arabidopsis leaves. Crucially, AMY3A suppression did not impair cassava stem cutting regrowth, highlighting it as a promising target for improving cassava root traits and advancing food security.