Table 1.

Molecular signaling mechanisms involved in aquaporin regulation under abiotic and biotic stresses and by endogenous signals

Type of Signal	Stimulus	Signaling Intermediate	Molecular Mechanism on Aquaporins	Aquaporin Regulation	References
Abiotic	Drought (ABA- dependent)	SnRK2.6	AtPIP2;1 loop B phosphorylation	Up-regulated activity	Grondin et al. (2015); Rodrigues et al. (2017)
		LP2	Interaction with OsPIP1;1, OsPIP1;3 and OsPIP2;3	Downregulated activity	Wu et al. (2015)
	Drought (ABA- independent)	RhPTM	Interaction with RhPIP2;1	ND	Zhang et al. (2019a, 2019b)
		TPSO	ND	AtPIP2;7 protein degradation	Hachez et al. (2014b)
		MtCas31/MtATG8	MtCas31 as a cargo receptor for MtPIP2;7	Protein degradation by autophagy	Li et al. (2020b)
	Osmotic	ND	Increased C-ter phosphorylation of AtPIP2;4	ND	Stecker et al. (2014)
		RBOHs and ROP6	Membrane lateral mobility	Clustering in nano-domains	Hosy et al. (2015); Martiniere et al. (2019); Smokvarska et al. (2020)
		clathrin	ND	Protein internalization	Zwiewka et al. (2015)
		Rma1H1	AtPIP2;1 ubiquitination	Protein degradation	Lee et al. (2009)
		UBC32	AtPIP2;1 ubiquitination	Protein degradation	Chen et al. (2021)
	Salinity	clathrin, PI3K, PI4K, SnRK2.4, SnRK2.10	C-ter phosphorylation of PIPs; enhanced mRNA decay	Protein internalization and down-regulated activity	Prak et al. (2008) Boursiac et al. (2008); Ueda et al., (2016); Pou et al., (2016); Kawa et al. (2020)
	O2 Availability	cytosolic protons	His protonation of PIPs	Downregulated activity	Tournaire-Roux et al. (2003)
		HCR1	ND	Downregulated activity	Shahzad et al. (2016)
	N	NRT2;1	ND	Enhanced gene expression, protein accumulation and upregulated activity	Li et al. (2016); Ishikawa-Sakurai et al. (2014)
	Cold	ND	AtPIP1;4 and AtPIP2;5 gene expression	Upregulation of gene expression	Rahman et al. (2020)
		OsCPK17	OsPIP2;1 and OsPIP2;6 C-ter phosphorylation	Upregulated activity	Almadanim et al. (2017)
	Circadian Clock	14-3-3	AtPIP2;1 C-ter phosphorylation	Upregulated activity	Prado et al. (2019)
		ELF3	AtPIP1;2 and AtPIP2;1 gene expression	Oscillating activity	Caldeira et al. (2014); Takase et al. (2011)
Biotic	flg22	BAK1 and SnRK2.6	Increased AtPIP2;1 loop B phosphorylation	Upregulated activity	Rodrigues et al. (2017)
	Phytophtora sojae	CRN78	GmPIP2;13 and NbPIP2;2 phosphorylation	Protein degradation	Ai et al. (2021)
	Chitin	CERK1 and LYK5	ND	Upregulated activity	Attia et al. (2020)
	Xanthomonas oryzae	Harpin	Interaction with OsPIP1;3 and AtPIP1;4	ND	Li et al. (2015b); Li et al. (2019)
Endogenous	Auxin	ARF7	PIP gene expression	Downregulated activity	Péret et al. (2012)
	MeJa	ND	PIP2 C-ter phosphorylation	Upregulated activity	Lee and Zwiazek (2019)
	Ethylene	RhETRs	RhPIP1;1 and RhPIP2;1 gene expression	Downregulated gene expression	Ma et al. (2008); Chen et al. (2013)
		ETR1 and CTR1	AtPIP2;1 C-ter phosphorylation	Upregulated activity	Yang et al. (2013); Qing et al. (2016)
	Sucrose	SIRK1, QSK1	AtPIP2;6 C-ter phosphorylation	Upregulated activity	Niittylä et al. (2007); Wu et al. (2013, 2014, 2019)
		BSK8	AtPIP2;7 C-ter phosphorylation	ND	Wu et al. (2014)
	CIF1 and CIF2	SGN3	ND	Downregulated activity	Wang et al. (2019)
	Other	CASPL1B1	Physical interaction with AtPIP2;1	Upregulated activity	Champeyroux et al. (2019)