Table 1.

Functional characterization of drought- and salt-inducible protein kinase and transcription factors originating from or expressed in trees species.

Genes	Sources	Abiotic and chemical elicitors	Functional characterization
			Promoter	Transgenic species	Phenotypes of stress tolerance	Functional traits of transgenics under stress conditions	References
SIGNAL PERCEPTION AND TRANSDUCTION
PYR/PYL/RCAR PYRL1 PYRL5	Populus trichocarpa	drought ABA	2x CaMV 35S	Populus davidiana x P. bolleana	Drought osmotic stress cold	↑ stomatal closure	Yu J. et al., 2017
						↑ drought tolerance
						↑ cold tolerance
						↑ osmotic stress resistance
						↓ water loss
PYR/PYL/RCAR PYRL1 PYRL5	Populus trichocarpa	drought ABA	2x CaMV 35S	A. thaliana	drought	↑ interaction with PP2C	Yu J. et al., 2016
						↑ ABA sensitivity
						↑ recovery after re-watering
						↓ seed germination
PP2C HAB1	Populus euphratica	drought ABA	CaMV 35S	A. thaliana	drought	↑ ABA response	Chen et al., 2015
						↑ drought sensitivity
						↑ interaction with PYL4 in yeast two-hybrid assays
MAPK MAPK1	Morus L	Drought Cold Heat NaCl	CaMV 35S	A. thaliana	NaCl H2O2	↑ NaCl tolerance	Liu et al., 2017
						↑ H2O2 tolerance
						↓ heat and drought tolerance
MYB MYB1	Fraxinus velutina	NaCl drought	CaMV 35S	Nicotiana tabacum	NaCl	↑ biomass production	Li et al., 2016
						↑ SOD and POD activity
						↑ proline content
NAC NAC034 NAC035 NAC045	Populus euphratica	Drought NaCl	CaMV 35S	A. thaliana P. tomentosa	drought NaCl	↑ root development	Lu et al., 2017
						↑ stem elongation
						↑ drought sensitivity
						↑ NaCl sensitivity
NAC NAC3	Cicer arietinum	drought ABA NaCl	CaMV 35S	Populus deltoides x P. euramericana	drought NaCl	↑ improved growth under drought, comparable to WT	Movahedi et al., 2015
						↑ proline content
						↑ photosynthetic pigments
						↑ antioxidant enzymes
NAC NAC13	Tamarix hispida	NaCl drought	CaMV 35S	Tamarix hispida A. thaliana	NaCl osmotic stress	↑ POD and SOD activity	Wang L. et al., 2017
						↑ proline content
						↑ chlorophyll content
						↓ ROS
						↓ MDA
NAC SNAC1	Phyllostachys edulis	auxin	CaMV 35S	A. thaliana	drought PEG	↑ survival rate under drought	Wang L. et al., 2016
						↑ overall growth
ErbB-3 binding protein1 EBP1	Hevea brasiliensis	cold drought ABA	CaMV 35S	A. thaliana	drought	↑ enhanced expression of RD29A, RD22 and CYCD3;1	Cheng et al., 2016
						↑ organ size
ZFP (zink finger protein) ZxZF	Zygophyllum xanthoxylum	drought	RD29A	thaliana Populus x euramericana	Mannitol ABA	↑ PSII activity	Chu et al., 2016
						↑ root growth
						↑ antioxidant enzymes
						↓ H2O2
EPF (epidermal patterning factor) PdEPF2	Populus nigra x (P. deltoids x P. nigra)	drought	CaMV 35S	A. thaliana	drought	↑ germination rate	Liu et al., 2016
						↑ primary root length
						↑ proline content
						↑ chlorophyll content
						↑ photosynthetic activity
CBF (C-repeat binding factor) CBF4	Populus euphratica	cold oxidative stress drought ABA NaCl	CaMV 35S	Populus tomentosa	drought ABA NaCl	↑ iWUE	Tian et al., 2017
						↑ photosynthesis rate
						↑ antioxidative enzymes
						↑ proline
						↓ overall growth (dwarf)
ERF ERF76	P. simonii x P. nigra	NaCl	CaMV 35S	P. simonii x P. nigra	NaCl	↑ ABA	Yao et al., 2016
						↑ GA
						↑ upregulation of 16 TFs and 45 stress related genes
START transcription factor EDT1/HDG11	A. thaliana	drought NaCl	CaMV 35S TUB2	Populus tomentosa, Gossypium hirsutum	drought NaCl	↑ proline content	Yu L. H. et al., 2016
						↑ soluble sugar content
						↑ antioxidant enzymes
						↑ NaCl tolerance
						↑ drought tolerance
CDPK (Calcium -dependent protein kinase) PeCPK10	Populus euphratica	Drought Salt Cold	CaMV 35S	A. thaliana	Drought Freezing	↑ expression of stress/ABA- responsive genes	Chen et al., 2013
bZIP (Basic leucine zipper protein) ThbZIP1	Tamarix hispida	NaCl PEG 6000 NaHCO3 CdCl2	CaMV 35S	Nicotiana tabacum	Salt	↑ activity of POD and SOD	Wang et al., 2010
						↑ soluble sugars
						↑ soluble proteins
Nucleoside diphosphate kinases NDPK2	Populus trichocarpa	ROS	CaMV 35S	Populus deltoides x P. euramericana	NaCl drought	↑ auxin related genes	Zhang et al., 2017
						↑ drought tolerance
						↑ NaCl tolerance
Nuclear factor Y NF-YB3	Picea wilsonii	NaCl heat PEG not ABA not cold	CaMV 35S	A. thaliana	drought NaCl ABA	↑ NaCl tolerance	Zhang et al., 2015
						↑ SOS3 transcript levels
						↑ drought tolerance
						↑ CDPK1 transcript levels
						↑ CBF marker genes
DREB (Dehydration -responsive element binding protein) PeDREB2a	Populus euphratica	Drought NaCl Low temperature NAA 6-BA GA3 Not by ABA	RD29A	A. thaliana Lotus corniculatus	Salt Drought	↑ root length and plant height ↑ soluble sugars levels ↓ MDA levels	Zhou et al., 2012
DREB PeDREB2	Populus euphratica	Drought High salinity Cold Not by ABA	CaMV 35S	Tobacco	High-salt	↑ seed germination ↑ chlorophyll levels ↑ chlorophyll fluorescence ↓ growth retardation	Chen et al., 2009
DREB PeDREB2L	Populus euphratica	dehydration salt ABA	CaMV 35S	A. thaliana	Drought Freezing	↑ DRE/CRT-containing stress- responsive genes, RD29A and RD29B	Chen et al., 2011
DREB ThDREB	Tamarix hispida	NaCl PEG NaHCO3 CdCl2	CAMV 35S	Tobacco Tamarix hispida (transient transgenic)	NaCl Mannitol	↑ antioxidase activity (SOD,POD) ↓ ROS (H2O2) ↓ MDA content ↓ electrolyte leakage (EL)	Yang et al., 2017
DREB DREB4A	Morus alba	cold drought	CaMV 35S	A. thaliana N. tabacum	Drought NaCl heat	↑ regulation of ABI1 and ABI2	Liu et al., 2015
						↑ proline content
						↓ MDA
						↑ NaCl, heat and droughttolerance in tobacco
DREB DREB2A	Fraxinus pennsylvanica	drought	2x CaMV 35S	Robinia pseudoacacia	drought	↑ stress-inducible genes	Xiu et al., 2016
						↑ ABA levels
						↑ auxin levels
						↓ GA levels
						↓ zeatin riboside
CBL PeCBL6 PeCBL10	Populus euphratica	Drought High salinity Cold Not by ABA	CAMV35S	A. thaliana	Salinity Drought Low temperature	↑ fresh mass, survival rate ↑ chlorophyll content ↑ chlorophyll fluorescence (Fv/Fm)	Li et al., 2013
NAC [No apical meristem (NAM), (CUC)] superfamily PeNAC1	Populus euphratica	Drought Salt stress ABA (slightly induced)	CaMV 35S	A. thaliana	Salt	↑ survival rates, fresh weights	Wang et al., 2013
						↑ capacity for K+ uptake and transport
						↓ AtHKT1 gene expression
						↓ Na+ content
NAC PeNAC036	Populus euphratica	Drought Salt ABA	CaMV 35S	A. thaliana (WT) and mutant anac072	Salt Drought	↑ plant height, primary root length (1/2 MS agar medium)	Lu et al., 2017
						↑ survival rate (Soil culture)
						↑ expression levels of COR47, RD29B, ERD11,RD22 and DREB2A
ERF (Ethylene) response factor ERF76	Populus simonii x Populus nigra	Drought Salinity ABA .	CaMV 35S	P. simonii x P. nigra	Salt	↑ Plant height, root length, and fresh weight	Wang et al., 2014 Yao et al., 2016
						↑ gene expression of ABA and GA signal pathways
						↑ defense-related genes, such as LEA, GST and HRGP genes
						↑ signal transfer-related Genes (incl). P-tyrosine phosphatases, MAPKKK and PR5K
WRKY ThWRKY4	Tamarix hispida	Drought Salt ABA	CaMV 35S	A. thaliana	ABA Salt Oxidative stress	↑ SOD and POD activity	Zheng et al., 2013
						↓ ROS level
						↓ cell death
ZFP (Zinc finger protein) ThZFP1	Tamarix hispida	NaCl Mannitol ABA	CaMV 35S	A. thaliana Tamarix hispida (transient overexpression or knockdown)	ABA NaCl Mannitol	↑ SOD and POD activity and encoding genes	Zang et al., 2015
						↑ proline level, and ThP5CS1&2 genes
						↑ chlorophyll content
						↓ ${\text{O}}_2^{-}$ and H2O2
						↓ MDA content, membrane lipid peroxidation, electrolytic leakage

Polyethyleneglycol (PEG), 1-naphthaleneacetic acid (NAA), 6-benzyl aminopurine (6-BA), gibberellic acid (GA), abscisic acid (ABA), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), Cauliflower mosaic virus (CaMV), Electrolyte leakage (EL), instantaneous water use efficieny (iWUE), ↑, Increase; ↓, Decrease.

Data were searched between 2013 and 2018 with the key words: Tree and overexpression and drought in Web of Science.