Table II. Comparison of different biochemical model structures using root length as a readout.

Biochemical model 1 assumes a preassembly between BRI1, SERK1, and SERK3 in the absence of ligand, while biochemical model 2 assumes only an interaction in the presence of ligand (Supplemental File S1A). The prediction errors of biochemical model 1, biochemical model 2, and the effect of changing the stoichiometry between BRI1, SERK1, and SERK3 are shown. A deviation of 10% in prediction error from the optimal value is considered to be significantly different.

Model	Stoichiometry, BRI1:SERK1:SERK3	Prediction Errora
Biochemical model 1	1:1	63
	1:2	67
	1:4	69
	2:2	105
Biochemical model 2	1:1	67
	1:2	65
	1:4	74
	2:2	106

^aAverage prediction error over four leave-one-out cross-validations.