Table 1.

PLSR model summaries of ¹³C-enriched VOCs (acetate, acetone and diacetyl⁺) fluxes after labelling with ¹³C2-pyruvate

VOC model	Gene	KO	Produce (p) or consume (c)	Variable (enzyme/VOC efflux/physiochemical)	VIP	PLSR weight
						w1	w2
Acetate	na	na	na	acetone-C2 efflux	1.51	0.61	0.28
	ACH1	K01067	p	acetyl-CoA hydrolase	1.21	0.48	0.15
	aarC	K18118	c	succinyl-CoA:acetate CoA-transferase	1.05	0.21	−0.23
	na	na	na	soil moisture (%)	1.02	−0.42	–
	poxL	K00158	p	pyruvate oxidase	0.92	0.17	−0.53
	poxB	K00156	p	PDH-quinone	0.90	0.18	−0.50
	acyP	K01512	p	acylphosphatase	0.86	–	0.28
	acs	K01895	c	acetyl-CoA synthase	0.82	−0.21	0.12
	pct	K01026	p	propionate CoA-transferase	0.82	−0.28	–
	ackA	K00925	c	acetate kinase	0.75	–	0.46
				R2- total 0.91 (6 comp.)		0.51	0.20
Acetone	na	na	na	acetate-C2 efflux	1.36	0.61	–
	adc	K01574	p	acetoacetate decarboxylase	1.05	0.47	–
	na	na	na	soil moisture (%)	1.00	−0.44	–
	adh1	K18382	c	NAD+-dependent secondary alcohol dehydrogenase	0.80	0.36	–
	acmA	K18371	c	acetone monooxygenase	0.64	−0.29	–
				R2- total 0.76 (1 comp.)		0.76	–
Diacetyl+	na	na	na	soil moisture (%)	1.12	–	0.99
	butA	K03366	c	meso-butanediol dehydrogenase	0.86	–0.99	–
				R2- total 0.23 (2 comp.)		0.15	0.08

PLSR models were created with single response variables (fluxes for each of the ¹³C-enriched VOCs) and predictor variables that included expression of genes known to produce or consume each ¹³C-enriched VOC and soil moisture (%). The VIP values represent the degree of importance of each predictor variable on the response variable. The PLSR weights (w) depict the magnitude and direction of contribution of each predictor variable (+ or − relationship) on the response variable along the first and/or second component (w1 and w2), with a dash indicating a lack of contribution to that component. Genes or physicochemical properties that were determined to not contribute to each model are not shown (see Methods). ¹³C-enriched VOC fluxes and gene expression data are from three collars that received ¹³C2-pyruvate at 0, 6 and 48 h post pyruvate injection during pre-drought and drought conditions (n = 18). The total percentage of variance explained (R²) from predictor variables for all components (comp., shown in parentheses) in the optimized model is shown in the bottom row for each VOC model in bold. The R² broken down by the first and second components are shown below w1 and w2, respectively, in bold. Acetone-C2 efflux was included in the model for acetate-C2, and acetate-C2 efflux was included in the model for acetone-C2 due to the high correlation between acetate-C2 and acetone-C2.

na, not applicable; +, C₄H₆O₂ represents diacetyl and/or one other unidentifiable compound.