A Mass Spectrometry Approach Reveals Fatty Acid Isomerism in Tomato Cold Tolerance

Plants can adapt to environmental fluctuations through modulating their fatty acids (FAs) dynamically. In this study, an enhanced mass spectrometry approach is utilized to uncover an unexplored landscape of FAs and FA isomers that are critical for cold tolerance in tomato. This technology integrates N-(4-aminomethylphenyl) pyridium derivatization of FAs, charge-tagging Paternò-Büchi (PB) photochemical reaction to identify carbon-carbon double bond (C═C) positions and reversed-phase liquid chromatography coupled with tandem mass spectrometry to achieve efficient detection of FAs and their C═C location isomers. Several saturated FAs, unsaturated FAs and their C═C location isomers are revealed to contribute to the cold tolerance of elongated hypocotyl 5 (slhy5) and fatty acid desaturase (slfad) mutant plants. RNA-sequencing analysis and dual-luciferase reporter assays further demonstrate that SlHY5 can modulate the expression of SlFAD2 genes under cold stress, regulating FA desaturation. The application of FA isomers to the leaves of slfad mutants partially rescues their cold sensitivity, presenting the practical implications of the study. The study thereby highlights the importance of considering isomeric variations in FAs when investigating plant physiology and stress responses. Furthermore, this methodology sets a valuable precedent for future investigations aimed at unraveling the intricate metabolic networks that govern plant stress adaptation.