Fig. 3. Expression of genes encoding enzymes that cycle ¹³C-enriched VOCs shifts with drought.

a, Pyruvate metabolism pathways that lead to ¹³C-enriched VOCs and CO₂, shown with blue and pink circles, to represent incorporation of ¹³C-pyruvate from the C1 and/or C2 position, respectively. Colour code for compound names: grey names without brackets indicate compounds that were not measured, grey names with brackets indicate VOCs that were not emitted, plain black names indicate VOC fluxes that were emitted but not ¹³C-enriched and bold black names indicate VOC emissions that were ¹³C-enriched (acetate, acetone, diacetyl⁺). Red arrows represent a potential PDH bypass route of acetyl-CoA production from pyruvate to acetate to acetyl-CoA. Green and orange gene names signify down- or upregulation during drought, respectively, compared to pre-drought conditions. b, Changes in gene expression across all sites (for pre-drought: 0 and 48 h (n = 6), 6 h (n = 5); for drought: n = 6 for each timepoint) as log₂ fold-change (log₂FC) of drought vs pre-drought for acetate, acetone and diacetyl⁺ (C₄H₆O₂) at 0, 6 and 48 h post pyruvate addition. Genes that encode enzymes involved in production are in black bars and consumption in grey bars. P values in b are based on DESeq2 and are FDR corrected. ^, anaplerotic CO₂ assimilation via pyc (pyruvate carboxylase) leading to some ¹³C from ¹³C1-pyruvate entering the TCA cycle and being released as ¹³C-CO₂. acxA–C, acetone carboxylase subunits A–C; ilvB, acetolactate synthase; cs, citrate synthase; ald1, NAD⁺-dependent secondary alcohol dehydrogenase; OAA, oxaloacetate; PEP, phosphoenolpyruvate. *P < 0.05, **P < 0.01, ***P < 0.001.

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