Table 1. Key peptide and nitrate substrate interacting amino acid residues from selected studies (Doki et al., 2013; Solcan et al., 2012; Parker and Newstead, 2014; Sun et al., 2014; Aduri et al., 2015; Newstead et al., 2011; Lyons et al., 2014; Jørgensen et al., 2015).

Corresponding residues in AtGTR1, AtGTR2, AtGTR3, CpGTRL1, CpGTRL2, Me14g74000 and MeCGTR1 were identified based on the alignment shown in Figure 8—figure supplement 1.

Position	Function	AtGTR1	AtGTR2	AtGTR3	CpGTRL1	CpGTRL2	Me14g74000	MeCGTR1		NPF6.3		PepT1	PepTSt	PepTGK	PepTS0
P1	EXXE[R/K] (Doki et al., 2013; Aduri et al., 2015; Jørgensen et al., 2015)	E75	E57	E33	E30	E49	E54	E38		E41		E23	E22	E32	E21
P2	EXXE[R/K] (Doki et al., 2013)	E78	E60	E36	E33	E42	E57	E41		E44		E26	E25	E35	E24
P3	EXXE[R/K] (Doki et al., 2013)	K79	K61	K37	K34	K43	K58	K42		R45		R27	R26	R36	R25
P4	Peptide specificity (Solcan et al., 2012)	I82	I64	I40	I37	I46	A61	T45		T48		Y30	Y29	Y39	F28
P5	Peptide specificity (Doki et al., 2013)	I83	I65	V41	I38	I47	I62	V46		L49		Y31	Y30	Y40	Y29
P6	Peptide specificity (Doki et al., 2013)	L86	L68	S44	L41	L50	L65	S49		G52		R34	R33	R43	R32
P7	Peptide binding (Doki et al., 2013)	N116	N98	N74	N71	N80	N95	N79		F82		Y64	Y68	Y78	Y68
P8	Exxer-interactor (Doki et al., 2013)	R196	R180	R156	R152	R162	R176	R161		K164		K140	K126	K136	K127
P9	Peptide binding (Doki et al., 2013)	T230	T214	T190	T186	T196	T210	T195		N198		N171	N156	N166	N158
P10	Peptidebinding /protonation (Parker and Newstead, 2014; Sun et al., 2014)	I385	I369	Y343	I341	V351	I365	L350		H356		F297	E299	Q309	F315
P11	Peptide specificity (Doki et al., 2013)	T386	T370	I344	I342	I352	V366	I351		A357		D298	E300	E310(Q)	D316
P12	Peptide binding (Doki et al., 2013)	L419	L403	L377	L375	L385	V399	T384		Y388		N329	N328	N342	N344
P13	Proton translocation (Doki et al., 2013)	E513	E497	D471	E469	E479	E493	E478		E476		E595	E400	E413	E419