Target of rapamycin kinase is involved in regulating maize radicle development through starch metabolism

Target of rapamycin (TOR) signaling plays a pivotal role in regulating various cellular processes, including energy metabolism and growth. In this study, we investigated the impact of TOR inhibition on maize radicle development, focusing on energy homeostasis and starch metabolism. We found that TOR inhibition significantly decreased the ATP/AMP ratio, indicating a disruption in cellular energy balance. This was accompanied by alterations in the expression of genes related to energy metabolism, such as STP1 (SUGAR TRANSPORTER PROTEIN 1) and ASN1 (Aspartate Aminotransferase 1). Transcriptomic and metabolomic analyses revealed significant changes in carbohydrate metabolism, particularly in starch degradation pathways, with key metabolites like glucose-6-phosphate (G6P) showing marked reductions. To further elucidate the role of starch metabolism in TOR-mediated regulation of radicle growth, we performed rescue experiments using exogenous soluble starch and maltose. Both treatments alleviated the inhibitory effects of TOR suppression, with radicle length increasing by 19.7% and 37.0%, respectively. These results highlight that TOR signaling regulates radicle development by modulating starch metabolism and energy homeostasis. Our findings provide new insights into the molecular mechanisms underlying TOR-mediated growth regulation and suggest that manipulating starch metabolism could be a potential strategy to enhance seedling development under stress conditions.