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. 2023 May 8;14:1146577. doi: 10.3389/fpls.2023.1146577

Table 1.

Chemical priming of plant defense responses to pathogens.

Plant species App1 Pathogens Lag2 Priming effect References
SA P. crispum L. sc. Medium3 Pmg 1 d4 Increased coumarin production upon low-dose elicitation. Kauss et al., 1992b
P. crispum L. sc. Medium3 Pmg 1 d4 Enhanced elicitation of the oxidative burst. Kauss and Jeblick, 1995
P. crispum L. sc Medium3 Pmg 22 h4 Potentiated expression of PAL, 4-coumarate:CoA ligase (4CL), PR10 and hydroxyproline-rich glycoprotein (HRGP) upon elicitor treatment. Thulke and Conrath, 1998; Conrath et al., 2006
Glycine max sc. Medium3 Psg NL11 Increased defense gene expression, H2O2 accumulation, and hypersensitive cell death upon Psg infection. Shirasu et al., 1997
P. crispum L. sc Medium3 Pep-13 1 d4 Enhanced induction of a rapid K+/pH response. Katz et al., 2002
Cucumis sativus L. hypocotyl – P. sojae
elicitor		 18 h Augmented H2O2 production upon treatment by elicitor from Phytophora sojae. Fauth et al., 1996
N. tabacum Hydroponic Pss 2774
TMV U1		 7 d5 Potentiation of defense genes AoPR1-GUS and PAL-GUS upon pathogen attack. Mur et al., 1996
A. thaliana Medium3 flg22 1 d4 Improvement of flg22-induced oxidative burst and callose deposition, requiring NPR1 downstream of SID2. Yi et al., 2014
A. thaliana – flg22 1 d4 Enhancement of dual phosphorylation of the TEY motif in MPK3 and MPK6 upon flg22 treatment, which requires NPR1. Yi et al., 2015
Pusa Ruby variety Spraying Rhizoctonia solani 1 d Induction of biosynthesis of SA, JA and polyphenols, stronger PR1a and PAD4 induction and limited pathogen-stimulated ROS production upon pathogen attack. Koley et al., 2022
BTH P. crispum L. sc. Medium3 Pmg 1 d4 Potentiated activation of PAL gene and enhanced coumarin secretion after elicitor application. Katz et al., 1998
Vigna unguiculata Seed soaking C. destru-ctivum 7 d Potentiation of PAL and CHI enzymes activity and kievitone and phaseollidin isoflavonoid phytoalexins accumulation after pathogen inoculation. Latunde-Dada and Lucas, 2001
A. thaliana Spraying Pst DC3000 3 d PAL gene activation and callose deposition after bacteria treatment requiring NPR1. Kohler et al., 2002
A. thaliana Spraying Pst DC3000 3 d Enhanced plant defense upon pathogen exposure. Full priming requires both MPK3 and MPK6. Beckers et al., 2009
A. thaliana Medium3 flg22 1 d4 Covalent modification of histone H3 and chromatin opening in the WRKY6 and PR1 regulatory regions and enhanced WRKY6 activation upon flg22 treatment. Schillheim et al., 2018
Oryza sativa cv. NB Soil6 Magnaporthe oryzae 1 d Increased diterpenoid biosynthesis upon infection by M. oryzae through SA/CK synergism in a WRKY45-dependent manner. Akagi et al., 2014
INA P. crispum L. sc Medium3 Pmg Potentiation of coumarin production upon low-dose elicitation. Kauss et al., 1992b
Cucumis sativus L. hypocotyl – P. sojae
elicitor		 18 h Augmented H2O2 production upon treatment by elicitor from Phytophora sojae. Fauth et al., 1996
Phaseolus vulagris L. Infiltration Pph 7 d Potentiation of induction of WRKY29 and WRKY53 gene expression upon pathogen exposure. Martínez-Aguilar et al., 2016
P. vulgaris L. cv. Riñón Spraying Pph or flg22 7 d Improvement of plant defense upon pathogen exposure by cell wall remodeling. De la Rubia et al., 2021
Pip A. thaliana Soil6 Psm ES4326 1 d Positive regulation of SA biosynthesis and strong potentiation of camalexin production, pathogen-triggered expression of ALD1, FMO1 and PR1. Návarová et al., 2012
N. tabacum Soil6 Pstb 6605
Psm ES4326		 1 d Rapid and strong accumulation of SA and nicotine following bacterial infection. Vogel-Adghough et al., 2013
A. thaliana Soil6 Psm ES4326
Psm lux
Hpa Noco2		 1 d Orchestration of SA-dependent and partially independent SAR transcriptional response, which depends on FMO1. Bernsdorff et al., 2016; Hartmann et al., 2018
NHP A. thaliana Soil6 Psm ES4326
Psm lux
Hpa Noco2		 1 d Improvement of pathogen-triggered activation of defense metabolism, including biosynthesis of SA, Pip, branched-chain amino acids and camalexin. Advanced SA- and pathogen-induced expression of defense-related genes requiring NPR1. Hartmann et al., 2018; Yildiz et al., 2021
A. thaliana Leaf inf7 Psm ES4326 1 d NHP moves systemically in Arabidopsis and rescues the SAR-deficiency of fmo1 mutants. Changes in SAR gene expression and enhancement of the hypersensitive response causing resistance to bacterial pathogens. Chen et al., 2018
AZA A. thaliana Leaf inf7 Psm ES4326 12 h - 48 h SA accumulation and enhanced PR1 expression in both local and systemic leaves. Priming in systemic leaves is dependent on the AZI1 gene. Jung et al., 2009
A. thaliana Leaf inf7 Psm ES4326 2 d Lipid transfer protein (LTP)-like AZI1 and its paralog EARLI1 are necessary for priming by AZA as shown by PR1 and LOX2 protein induction. Cecchini et al., 2015
BABA A. thaliana – Pst DC3000 1 d PR1 gene expression is enhanced upon pathogen attack. Zimmerli et al., 2000
A. thaliana – P. parasitica 1 d Induction of resistance by callose deposition, hypersensitive response and necrosis formation. Resistance does not require SA, JA, ET or SAR signaling pathways. Zimmerli et al., 2000
A. thaliana – Pst DC3000 2 d Induction of SA-dependent defense responses leading to enhanced PR1 gene expression and necrosis formation. Ton et al., 2005
A. thaliana – Hpa 2 d Induction of SA-dependent defense responses leading to enhanced necrosis. Priming of phosphatidylinositol- and ABA-dependent defense responses resulting in increased callose deposition. Ton et al., 2005
A. thaliana Soil6 Pst DC3000 2 d Enhancement of resistance to pathogen exposure. Potentiation of induction of PR1 expression upon pathogen exposure. L-glutamine treatment inhibits BABA-induced resistance. Wu et al., 2010
A. thaliana Soil6 Pst DC3000 2 d Faster and stronger induction of SA signaling genes upon pathogen attack. Slaughter et al., 2012
A. thaliana Soil6 Pst DC3000 1 - 2 d Priming by the production of amino acids, IAA, SA and SA-glucosides, and xanthosine. BABA boosts plant primary metabolism by induction of tricarboxylic acids and potentiates phenylpropanoid biosynthesis and the octodecanoic pathway. Pastor et al., 2014
A. thaliana Soil6 (for 6 d), Rep8 Pst DC3000 luxCDABE or Hpa or SA 1, 8, 15 and 21 d Induction of short-term resistance, which is independent of NPR1 and long-term resistance, which depends on NPR1 and involves priming of SA-regulated defense genes. The histone methyltransferase SUVH4/KRYPTONITE (KYP) is required for maintaining the primed state. Luna et al., 2014a
A. thaliana Soil6 Hpa strain WACO9 or CALA-2 2 d The interaction of BABA with IMPAIRED IN BABA-INDUCED IMMUNITY1 (IBI1) primes pathogen defense responses. Luna et al., 2014b
A. thaliana Soil6 Hpa strain WACO9 2 d Binding of BABA to endoplasmic reticulum-located IBI1 primes the translocation of IBI1 to the cytosol. Cytosolic IBI1 interacts with VOZ1/2 transcription factors, thereby suppressing pathogen-induced ABA signaling. Schwarzenbacher et al., 2020
Vitis vinifera – P. viticola 1 d Induction of resistance involving callose deposition, phenylpropanoid-dependent defense mechanisms and JA signaling. BABA pre-treatment potentiates the expression of SA and JA signaling genes upon pathogen exposure. Hamiduzzaman et al., 2005
S. tuberosum
cv. Desiree		 Spray9 P. infestans 2 d Induction of resistance involving PR protein accumulation. Bengtsson et al., 2014
S. lycopersicum Soil6 B. cinerea 5 d Induction of plant resistance. Luna et al., 2016
Phaseolus vulgaris L. Soil6 Pph 7 d Priming of plant defense upon pathogen exposure. Potentiation of induction of PR1, PR4, NPR1, WRKY6, WRKY29 and WRKY53 gene expression upon pathogen exposure, while BABA treatment itself is ineffective modification of chromatin marks. Martínez-Aguilar et al., 2016
L. sativa romaine cv. Parris island Soil6 S. enterica serovar typhimurium 1 d Induction of resistance by enhanced expression of PR1 upon pathogen attack. Chalupowicz et al., 2021
N. tabacum L. Spray9 (for 3 d) P. parasitica 3 d Hydrogen peroxide accumulation results in the activation of plant defense. Enhancement of callose deposition, production of SA and JA-Ile and expression of SA-, JA- and ET signaling genes upon pathogen exposure. Ren et al., 2022
S. lycopersicum L. cv. Money Maker Root10 (for 7 d) Rep8 B. cinerea 10 d Priming of both SA- and JA-dependent resistance. BABA treatment results in genome-wide DNA methylation. Catoni et al., 2022
tZ A. thaliana Spray9 Pst DC3000 1 d Potentiation of the activation of SA defense-related gene PR1 upon bacteria inoculation. Choi et al., 2010
N. tabacum
leaves		 Petiole feeding Pstb 1 d12 Enhanced resistance against bacteria; mode of action not studied Großkinsky et al., 2011
KIN N. tabacum
leaves		 Petiole feeding Pstb 1 d12 A high phytoalexin-pathogen ratio in the early phase of infection efficiently restricted pathogen growth. Großkinsky et al., 2011
BAP N. tabacum
leaves		 Petiole feeding Pstb 1 d12 Enhanced resistance against bacteria; mode of action not studied. Großkinsky et al., 2011
A. thaliana Spray9 Hpa Noco2 2 d Enhanced resistance against Hpa in a dose‐dependent manner. SA-responsive defense genes were up-regulated in response to BAP pretreatment and inoculation with Hpa Noco2. Argueso et al., 2012
MeJA Petroselinum crispum L. suspension culture Medium3 Pmg 1 d4 Pretreatment augmented secretion of coumarin derivatives and incorporation of esterified hydroxycinnamic acids and “lignin-like” polymers into the cell wall after elicitor treatment. Kauss et al., 1992a
A. thaliana Dipping Pst DC3000 3 d Priming was impaired in JA response mutant jar1, the ET response mutant etr1 and dependent on NPR1. Pieterse et al., 1998
Phaseolus vulgaris L. Spray9 Sclerotinia sclerotiorum (Lib.) de Bary 12 h Pretreatment-induced systemic upregulation of PvChit1/PR3 (chitinase), PvCallose (callose synthase), PvNBS-LRR (NBS-LRR resistance-like protein), and PvF-box (F-box family protein-like) genes after pathogen infection. Oliveira et al., 2015
Tomato Pusa Ruby variety Spray9 Rhizoctonia solani 1 d Higher resistance to pathogen attack. Induction of biosynthesis of SA, JA and polyphenols. Stronger PR1a and PAD4 expression induction and reduction of pathogen-stimulated ROS production. Weaker and slower effect than SA in the same experiment. Koley et al., 2022
Hx S. lycopersicum cv. Ailsa Craig Hydroponic conditions B. cinerea 2 d Negative effect on fungal membrane permeability. Improvement of plants’ resistance either if the compound stays on the plant or if it is washed away before pathogen exposure indicating priming. Leyva et al., 2008
S. lycopersicum Mill (wild-type Ailsa Craig, Rheinlands Ruhm, Moneymaker, and Castlemart) Root B. cinerea or P. syringae 2 d Induction of resistance to different pathogens. The Hx-induced resistance is not SA-dependent. Induction of ABA-dependent callose deposition. In addition, activation of JA-dependent defense responses involving priming of 12-oxo-phytodienoic acid (OPDA) and JA-isoleucine accumulation. Vicedo et al., 2009
S. lycopersicum Mill. cv. Ailsa Craig Hydroponic conditions or soil6 Pst DC3000 or P. syringae strain cmaA lacking coronatine 2 - 3 d Counteraction of the negative effects of JA-Ile and coronatine on SA signaling. The JA-precursor OPDA accumulates in Hx-treated plants upon infection. Accumulation of transcripts, such as LoxD and OPR3, which are involved in OPDA- and JA biosynthesis. Potentiation of the expression of SA signaling genes, such as PR1 and PR5, upon pathogen infection, while the expression of ABA- and ET-related genes is not affected. Inhibition of stomatal re-opening mediated by coronatine, thereby probably preventing the entry of the bacteria to the plant mesophyll. Scalschi et al., 2013
S. lycopersicum cv. Ailsa Craig Root B. cinerea 2 d Priming the plants’ resistance to pathogen attack. Decreased accumulation of ROS in tomato upon pathogen attack. Enhanced expression of similar tomato genes as following Botrytis infection. Finiti et al., 2014
A. thaliana Soil6 B. cinerea 2 d Induction of resistance to pathogen attack. Hx-induced resistance is dependent on JA but independent of ABA, SA, ET and glutathion signaling or callose deposition. Kravchuk et al., 2011
Citrus clementina grafted onto Carrizo citrange 13 Soil6 A. alternata 2 - 3 d Activation of mevalonic and linolenic acid pathways upon pathogen attack. Hx stays in the root and induces distal resistance. Enhanced emission of volatile metabolites. Llorens et al., 2016
GABA A. thaliana Spray9 B. cinerea Up to 4 d Decreased accumulation of ROS upon Botrytis infection involving increased activities of catalase and guaiacol peroxidase. Janse van Rensburg and van den Ende, 2020
LOS Lactuca sativa var. Gisela Spray9 B. cinerea 3 d Improvement of the plants’ resistance to pathogen attack involving the accumulation of hydrogen peroxide and GABA. ET signaling is essential. Tarkowski et al., 2019 and Tarkowski et al., 2020
A. thaliana Spray9 B. cinerea 3 d Inulin and levan oligosaccharide (LOS) enhance plant defense upon pathogen exposure. Fructan pre-treatment enhances hydrogen peroxide accumulation and increases the activity of antioxidant enzymes (catalase, ascorbate peroxidase) upon pathogen exposure. In addition, glucose, sucrose and total soluble sugars accumulate in plants pre-treated with fructans. Janse van Rensburg et al., 2020

1App, application of chemical priming agents; 2Lag, time lag between chemical treatment and pathogen infection; 3Medium, compounds were added into the media; 4Time period between compound addition into the media and the pathogen or the elicitor treatment. It is arguable whether this represents a lag phase; 5Duration entire plant pots were submerged into the SA solution. It is arguable whether this represents a lag phase; 6Soil, soil-drenching; 7Leaf inf, leaf infiltration; 8Rep, repotting of plants after chemical priming; 9Spray, spraying of chemical priming agent; 10Root, root-drenching. 11NL, no lag phase; 12Time leaves were fed with CK. It is arguable whether this represents a lag phase; 13 Citrus clementina grafted onto Carrizo citrange, Citrus clementina (hort. ex Tanaka x Dancy mandarin) grafted onto Carrizo citrange plants (Citrus sinensis L. Osbeck x Poncirus trifoliata Blanco).

Pep-13, elicitor-active 13-amino acid oligopeptide derived from the Pmg elicitor; TMV, tobacco mosaic virus; Pmg, cell wall elicitor from Phytophthora megasperma f. sp. glycinea; Psg, Pseudomonas syringae pv. glycinea; sc, suspension culture; Pph, P. syringae pv. phaseolicola; Pss, P. syringae pv. syringae; Pst, P. syringae pv. tomato; Pstb, P. syringae pv. tabaci; Psm, P. syringae pv. maculicola; Hpa, Hyaloperonospora parasitica; AZA, azelaic acid; BABA, beta-aminobutyric acid; BAP, 6-benzylaminopurine; BTH, benzothiadiazole; GABA, gamma- aminobutyric acid; Hx, hexanoic acid; INA, 2,6-dichloroisonicotinic acid; KIN, kinetin, 6-furfurylaminopurin; LOS, inulin and levan oligosaccharide; MeJA, methyl jasmonate; NHP, N-hydroxypipecolic acid; Pip, pipecolic acid; SA, salicylic acid; tZ, trans-zeatin.