Mechanism by Which Karrikin Priming Promotes Seed Germination of Isodon serra Under Heat Stress: Insights from Integrated Transcriptomic and Metabolomic Analyses

Isodon serra is a medicinal plant distributed in the Lingnan region of China. However, I. serra seeds are sensitive to heat, limiting germination in Lingnan’s climate. Seed priming technology provides an effective means to address this problem. Meanwhile, karrikin (KAR) enhances plant growth and stress tolerance, but its mechanism in I. serra remains unclear. Therefore, in this study, different KAR concentrations were selected for priming to examine the phenotypic and physiological responses, and multi-omics analysis was used to explore the molecular mechanism of promoted germination under heat stress. The optimal concentration of 0.05 µmol/L KAR raised the seed germination rate under heat stress. This priming treatment reduced membrane damage, indicated by lower malondialdehyde (MDA) levels and relative electrical conductivity (REC) and oxidative stress, by regulating antioxidant enzymes and increasing glutathione (GSH) content. Multispectral phenotyping revealed distinct spectral features at 880 nm and 970 nm in primed seeds, correlating with enhanced vigor. Integrated multi-omics analysis demonstrated that the alleviation of heat stress was primarily mediated through the glutathione metabolism pathway, with key roles played by genes such as cluster-23509.3, cluster-15076.0, and cluster-22471.0. In summary, KAR priming enhances osmotic adjustment, improves reactive oxygen species (ROS)-scavenging enzyme activities, and regulates glutathione metabolism to mitigate heat stress in I. serra. These findings provide valuable insights for optimizing the cultivation and management of I. serra under heat stress conditions.