Table 1.

Signaling components involved in metal stress.

Heavy metal	Plant	Signaling components
		MAPK	Calcium	Hormone
Cd	Arabidopsis	MEKK1, MPK3, MPK6 (Jonak et al., 2004; Liu et al., 2010)	Unknown	Auxin: 2PAT1, 2CYP79B2, 2CYP79B3, 2YUCCA, 2GH3, 2TIR1, 1, 2, 3PINs, 2ABCB, 2ARFs, 3AXR3/IAA17 (1Hu et al., 2013; 2Wang et al., 2015; 3Yuan and Huang, 2016) Cytokinin: IPT, CKX (Vitti et al., 2013) Ethylene: 4, 5ACS, 5ACC, 4ETR2, 4ERF1,5, 5GSH1, 5GSH2 (4Weber et al., 2006; 5Schellingen et al., 2015)
	Rice	MAPK2, MPK3, MPK6, MSRMK3, WJUMK (Agrawal et al., 2003; Yeh et al., 2007; Rao et al., 2011)	Unknown	Auxin: MAPK3/6/7, YUCCA, PINs, ARF, and IAA (Zhao et al., 2014)
	M. sativa	SAMK, SIMK, MMK2, MMK3 (Jonak et al., 2004)	Unknown	Unknown
	Zea mays	MPK3 (Wang et al., 2010)	Unknown	Unknown
	Radish	Unknown	Ca2+/CaM (Rivetta et al., 1997)	Unknown
	B. natalensis, R. crispus	Unknown	Unknown	Cytokinin: PI-55, INCYDE (Gemrotová et al., 2013)
	Glycin max	Unknown	Unknown	Ethylene: ACS, MAPK2, MAPKK2 Chmielowska-Bak et al., 2014
Cu	Arabidopsis	MPK3, MPK6 (Liu et al., 2010; Schellingen et al., 2015)	Unknown	Auxin: 2PAT1, 2CYP79B2, 2CYP79B3, 2YUCCA, 2GH3, 2TIR1, 2PINs, 2ABCB, 2ARFs, 1, 2DR5 (1 Peto et al., 2011; 2Wang et al., 2015) Ethylene: 4COPT5, 3ACS, 3ERF (3Weber et al., 2006; 4Carrió-Seguí et al., 2015)
	Rice	MAPK2, MPK3, MPK6, MSRMK3, WJUMK (Agrawal et al., 2003; Yeh et al., 2007; Rao et al., 2011)	Unknown	Unknown
	M. sativa	SIMKK, SAMK, SIMK, MMK2, MMK3 (Jonak et al., 2004)	Unknown	Unknown
As	Arabidopsis	Unknown	Unknown	Auxin: AUX1, PIN1, PIN2 (Krishnamurthy and Rathinasabapathi, 2013) Ethylene: ERFs (Fu et al., 2014)
	Rice	MKK4, MPK3, MPK4 (Rao et al., 2011)	CaM, CaM kinase, CaM like protein (Chakrabarty et al., 2009; Huang et al., 2012)	Unknown
	B. juncea	46Kda MAPK (Gupta et al., 2009)	Unknown	Unknown
Al	Arabidopsis	Unknown	Unknown	Auxin: 1, 2PIN2, 2AUX1 (1Shen et al., 2008; 2Sun et al., 2010)
	Wheat	Unknown	Myosin, Calpain, Phospholipase C, Phospholipase A2 (Jones and Kochian, 1997)	Unknown
	T. aestivum	48Kda MAPK, 42Kda Protein kinase (Osawa and Matsumoto, 2001)	Unknown	Ethylene: 3ALMT1, 4ACS, 4ACO (3Tian et al., 2014; 4Yu et al., 2016)
	M. sativa	Unknown	Unknown	Auxin: AUX1, PIN2 (Wang S. et al., 2016)
Hg	Arabidopsis	Unknown	Unknown	Auxin: PAT1, CYP79B2, CYP79B3, YUCCA, GH3, TIR1, PINs, ABCB, ARFs (Wang et al., 2015)
	Rice	MSRMK2, MSRMK3, WJUMK (Agrawal et al., 2003)	Unknown	Ethylene: OsACS2, OsACO1, OsACO2, OsACO5 and OsACO6, 5 MAPKKK, 1 MAPKK and 2 MAPK (Chen et al., 2014)
	M. sativa	Unknown	Unknown	Ethylene: ACCS, ACCO, AP2, ERF1 (Montero-Palmero et al., 2014)
Pb	Arabidopsis	Unknown	CNGC1 (Sunkar et al., 2000)	Auxin: PAT1, CYP79B2, CYP79B3, YUCCA, GH3, TIR1, PINs, ABCB, ARFs (Wang et al., 2015) Ethylene: EIN2 (Cao et al., 2009)
	Rice	34Kda, 40Kda & 42Kda MAPK (Huang and Huang, 2008)	CDPK-like Kinase (Huang and Huang, 2008)	Unknown
	tobacco	Unknown	CBP4 (Arazi et al., 1999; Sunkar et al., 2000)	Unknown
	R. sativus	MAPKKK7, MAPK6, MAPK18, MAPK20 (Wang et al., 2013)	Unknown	Unknown
Zn	Arabidopsis	Unknown	Unknown	Auxin: PAT1, CYP79B2, CYP79B3, YUCCA, GH3, TIR1, PINs, ABCB, ARFs (Wang et al., 2015)
	Rice	34Kda, 40Kda & 42Kda MAPK (Lin et al., 2005)	Unknown	Auxin: MAPK3/6/7, YUCCA, PINs, ARF, and IAA (Zhao et al., 2014)
	Wheat	Unknown	Myosin, Calpain, Phospholipase A2 (Jones and Kochian, 1997)	Unknown
Cr	Zea mays	MPK5 (Ding et al., 2009)	Unknown	Unknown
	Foxtail millet	Unknown	TPC1, MRC5, CaM (Fang H. et al., 2014)	Unknown
Mn	Arabidopsis	Unknown	ECA1 (Wu et al., 2002)	Unknown
Ni	Arabidopsis	Unknown	Unknown	Auxin: PAT1, CYP79B2, CYP79B3, YUCCA, GH3, TIR1, PINs, ABCB, ARFs (Wang et al., 2015)
	Tobacco	Unknown	CBP4 (Arazi et al., 1999)	Unknown
Ba	Faba bean	Unknown	Ca2+ channels (Hamilton et al., 2001)	Unknown
B	Barley	Unknown	Calmodulin, Ca2+- binding proteins (Tombuloglu et al., 2015)	Unknown