Potassium-regulated sucrose and trehalose-6-phosphate metabolism underpins root adaptation to drought in sweet potato (Ipomoea batatas (L.) Lam): an integrated transcriptomic and metabolomic study

Sweet potato (Ipomoea batatas (L.) Lam.) is an important food crop worldwide, but its production is often constrained by drought and low soil potassium (K) availability. However, how K supply under drought regulates root differentiation and drought tolerance in sweet potato remains poorly understood. In this study, the cultivar ‘Yanshu 25’ was grown under drought conditions either without K supply (CK) or with K supply (T). Root architectural traits, transcriptomic profiles and broadly targeted metabolomes were analyzed to elucidate K-mediated responses at the branching stage. K application markedly promoted root system restructuring, increasing total root length and root tip number by 2.3 and 3.2-fold, respectively, compared with CK, indicating enhanced root extension and branching capacity under water deficit. RNA-seq identified 9,397 differentially expressed genes (DEGs) between CK and T, which were significantly enriched in pathways related to primary and secondary metabolism, plant hormone signal transduction, and starch and sucrose metabolism. Metabolite profiling revealed 2,595 differentially accumulated metabolites (DAMs), with amino acids and their derivatives, organic acids and phenolic compounds as the predominant classes. Integrated transcriptomic–metabolomic analysis highlighted sucrose and trehalose-related metabolism as a central node in the K response. In K-treated roots, invertase (INV) and β-glucosidase (BGL) genes were up-regulated, whereas trehalose-6-phosphate synthase (TPS) was down-regulated, accompanied by increased sucrose and UDP-glucose and decreased trehalose-6-phosphate (T6P) levels. These coordinated changes are consistent with enhanced sucrose turnover and hexose provision, attenuation of T6P signaling and a shift in carbon allocation towards root development and stress-related processes. Collectively, our results reveal how K supply under drought couples root system architectural plasticity with transcriptional and metabolic reprogramming of carbon and nitrogen (N) metabolism and signaling pathways, providing a physiological and molecular basis for improving sweet potato drought tolerance through optimized K nutrition management.