Integrated lipidomic and transcriptomic analysis reveals triacylglycerol accumulation in castor bean seedlings under heat stress

Heat stress is one of the most challenging environmental factors for plants, which have evolved various mechanisms to cope with it. However, the role of lipid remodeling caused by heat stress is not yet fully understood. Here, we integrated UPLC-QTOF/MS-based lipidomic and transcriptomic analyzes to uncover the molecular basis of lipid remodeling under heat stress in castor bean (Ricinus communis), an important non-edible oil crop. We detected 297 lipid compounds in castor bean seedlings, of which 54 displayed altered abundances under heat stress. In particular, polyunsaturated triacylglycerols (TAGs) (e.g., TAG54:6, TAG54:7, TAG54:8, and TAG54:9) and diacylglycerols (DAGs) (DAG36:6) significantly increased, while polyunsaturated monogalactosyldiacylglycerols (MGDGs) (MGDG34:3) markedly decreased. When heat stress was subsequently relieved, these lipid molecules recovered to their normal levels. We found that heat-induced TAGs primarily accumulate in the cytosol. Transcriptomic analysis indicated that polyunsaturated fatty acids (FAs) used for TAGs are not derived from de novo synthesis, but likely from the lipids remodeling via lipase activity, and are subsequently esterified into TAGs via diacylglycerol acyltransferase (DGAT). Our results suggest that TAGs may act as intermediates in lipid turnover and provide one mechanism by which plants respond to heat stress, broadening our understanding of how lipid remodeling functions in plant adaptation to heat stress.