Cooperative contribution of multiple energy substrate pathways to floral thermogenesis in sacred lotus.

Floral thermogenesis in lotus (Nelumbo nucifera) is a highly energy-intensive process, requiring substantial metabolic reconfiguration and substrate input. However, the mechanisms coordinating energy substrate supply during this process remain unclear. Here, we integrated microscale proteomics, time-series transcriptomics, and mitochondrial feeding assays to elucidate the substrate provisioning strategies supporting thermogenesis in lotus receptacles. Proteomic analysis revealed a concerted upregulation of major energy metabolism pathways at the thermogenic initiation stage, accompanied by enhanced expression of energy dissipation-related proteins (alternative oxidase and uncoupling proteins), indicative of a metabolic shift favoring heat production over ATP synthesis. Our results highlight the cooperative contribution of multiple pyruvate sources to mitochondrial respiration. Both the mitochondrial pyruvate carrier (MPC)-mediated cytosolic pyruvate import and the NAD-dependent malic enzyme (NAD-ME)-derived intramitochondrial pyruvate flux were significantly elevated at the thermogenic stage. Notably, isotopic feeding experiments revealed that NAD-ME-derived pyruvate may contribute more substantially than MPC-derived pyruvate under thermogenic conditions, reflecting a highly flexible substrate utilization strategy. In addition, increased expression of alanine aminotransferase (AlaAT) and β-oxidation-related genes suggested that alanine transamination and fatty acid degradation may further expand the respiratory substrate pool. Collectively, this study uncovers a diverse and dynamic landscape of energy substrate supply that underpins heat production in thermogenic lotus tissues. These findings offer insights into how plants coordinate metabolic flexibility to meet the high energetic demands of floral thermogenesis.