Plants have acquired adaptive strategies in due course of time. Upon perception of pathogen, the plant immune system is primed, establishing an immune memory that allows primed plants to respond efficiently to the invading pathogen. Upon stimulus, perception change may occur in plants physiological, transcriptional, metabolic and epigenetic levels (Mauch-Mani et al., 2017). An alternative to plant diseases is the use of resistance inducers.
Some natural priming compounds are N-hydroxypipecolic acid (NHP) and Pipecolic acid (Pip), Azelaic acid (AA), Salicylic acid (SA), Methyl jasmonate (MeJA), Beta-aminobutyric acid (BABA), Gamma-aminobutyric acid (GABA), Cytokinin and Hexanoic acid (Aranega-Bou et al., 2014; Honig et al., 2023).
- N-hydroxypipecolic acid is crucial for the induction and maintenance of SAR. NHP application indicates chemical or metabolic engineering approach can prime or enhance disease resistance in plants under pathogen attack (Chen et al., 2018). NHP is biosynthesized with its precursor Pip and SA in monocotyledonous and dicotyledonous plants in response to the pathogenic attack thereby implicating NHP as a phloem-mobile immune signal acting as inducer of acquired resistance (Schnake et al., 2020).
- Exogenous application of pipecolic acid increase wild-type plant resistance against pathogen (Navarova et al., 2012). Pip orchestrates defense amplification, regulation of SA biosynthesis, induces local resistance and establishment of SAR (Navarova et al., 2012). Exogenous application of Pip enhance resistance to bacterial infection. Pip thereby primes tobacco for rapid accumulation of SA and nicotine upon infection (Vogel-Adghough et al., 2013).
- Azelaic acid a nine-carbon dicarboxylic acid primes plant to accumulate SA upon infection. An increased accumulation of AA in the vascular sap of Arabidopsis upon infection confers local and systemic resistance against the bacterial pathogen Pseudomonas syringae (Jung et al., 2009). Yu et al.(2013) demonstrated that systemic acquired resistance (SAR) induced by AA requires phosphorylated sugar derivative glycerol-3-phosphate. Pathogen inoculation induced the release of unsaturated fatty acids (FAs) and thereby triggered AA accumulation, as these FAs serve as precursors for AA (Yu et al., 2013).
- Salicylic acid in plants regulates both local disease resistance mechanisms, including host cell death and defense gene expression and SAR (Vlot et al., 2009).Chemical defense inducer benzothiadiazole (BTH) as well as exogenously applied SA induce defense response through SA signaling pathway thereby protecting plant from invading pathogen (Akagi et al., 2014). BTH a synthetic activator of acquired resistance in plants primes parsley cells for augmented elicitation of coumarine phytoalexin secretion (Katz et al., 1998).
- Methyl jasmonate is identified as vital cellular regulator, mediates defense responses against biotic and abiotic stress (Cheong and Choi 2003). Exogenous application of MeJA induces release of volatile organic compounds like those induced by herbivores in plants (Amo et al., 2022). Both jasmonate-based and salicylate-based elicitors show suppressive effects on fungal diseases and insect pests of plants (Holopainen et al., 2009).
- BABA is a chemical priming agent and can induce disease resistance in wide range of plant species against different pathogens (Cohen et al., 2016). Seed priming on exogenous application of phytohormone SA and JA and plant natural product BABA, induces crop disease resistance (Yang et al., 2022). BABA induces disease resistance but may repress plant growth which limits its exploitation in crop protection (Buswell et al., 2018). BABA-mediated papilla formation after oomycetepathogen Peronospora parasitica infection is independent of the SAR signaling Pathway (Zimmerli et al., 2000).
- GABA accumulates in plants under various stress and participate in defense responses as a defensive substance and as signaling molecule. GABA improves plants tolerance to oxidative stress. Exogenous GABA application is an effective and sustainable strategy to improve tolerance of plant to environmental biotic and abiotic stress (Guo et al., 2023).
- The effect of exogenous cytokinin on resistance response of wheat to powdery mildew (Erysiphe graminis f. sp. tritici Marchal), in which a dose-response curve of pathogen growth was obtained in response to exogenous zeatin (Babosha 2009). High concentration of cytokinin leads to elevated defense response to virulent oomycetes pathogen through a process that is dependent on SA accumulation and activation of defense gene expression (Argueso et al., 2012).
- Hexanoic acid is a potent natural priming agent in a wide range of host plant and pathogens (Aranega-Bou et al., 2014). Early it can induce callose deposition, SA and JA pathway as well as later it can prime pathogen-specific responses according to the pathogen lifestyle (Aranega-Bou et al., 2014). Root treatment with hexanoic acid protects tomato plants against Botrytis cinerea. Callose, oxylipins and the JA-signaling pathway are involved in hexanoic acid-induced resistance against B. cinerea (Vicedo et al., 2009).
References:
Akagi, A., Fukushima, S., Okada, K., Jiang, C-J., Yoshida, R., Nakayama, A., Shimono, M., Sugano, S., Yamane, H. and Takatsuji, H. 2014 WRKY45-Dependent Priming of Diterpenoid Phytoalexin Biosynthesis in Rice and the Role of Cytokinin in Triggering the Reaction. Plant Mol. Biol. 86(1): 171 – 183
doi: 10.1007/s11103-014-0221-x
Amo, L., Mrazova, A., Saavedra, I. and Sam, K. 2022 Exogenous Application of Methyl Jasmonate Increases Emissions of Volatile Organic Compounds in Pyrenean Oak Trees, Quercus pyrenaica. Biology (Basel) 11(1): 84
doi: 10.3390/biology11010084
Aranega-Bou, P., de la O Leyva, M., Finiti, I., Garcia-Agustin, P. and Gonzalez-Bosch, C. 2014 Priming of Plant Resistance by Natural Compounds Hexanoic Acid as a Model. Front Plant Sci. 5: 488
doi: 10.3389/fpls.2014.00488
Argueso, C. T., Ferreira, F. J., Epple, P., To, J. P. C., Hutchison, C. E., Schaller, G. E., Dangl, J. L. and Kieber, J. J. 2012 Two-Component Elements Mediate Interactions between Cytokinin and Salicylic Acid in Plant Immunity. PLoS Genet. 8(1): e1002448
doi: 10.1371/journal.pgen.1002448
Babosha, A. V. 2009 Regulation of Resistance and Susceptibility in Wheat-Powdery Mildew Pathosystem with Exogenous Cytokinins. J. Plant Physiol. 166(17): 1892 – 1903
doi: 10.1016/j.jplph.2009.05.014
Buswell, W., Schwarzenbacher, R. E., Luna, E., Sellwood, M., Chen, B., Flors, V., Petriacq, P. and Ton, J. 2018 Chemical Priming of Immunity without Costs to Plant Growth. New Phytol. 218(3): 1205 – 1216
doi.org/10.1111/nph.15062
Chen, Y-C., Holmes, E. C., Rajniak, J. and Sattely, E. S. 2018 N-Hydroxy-Pipecolic Acid is a Mobile Metabolite that Induces Systemic Disease Resistance in Arabidopsis. PNAS USA 115(21): E4920-E4929
doi.org/10.1073/pnas.1805291115
Cheong, J-J. and Choi, Y. D. 2003 Methyl Jasmonate as a Vital Substance in Plants. Trends Genet. 19(7): 409 – 413
doi: 10.1016/S0168-9525(03)00138-0
Cohen, Y., Vaknin, M. and Mauch-Mani, B. 2016 BABA-Induced Resistance: Milestones Along a 55-Year Journey. Phytoparasitica 44(4): 513 – 538
doi: 10.1007/s12600-016-0546-x
Guo, Z., Gong, J., Luo, S., Zuo, Y. and Shen, Y. 2023 Role of Gamma-Aminobutyric Acid in Plant Defense Response. Metabolites 13(6): 741
doi.org/10.3390/metabo13060741
Holopainen, J. K., Heijari, J., Nerg, A. M., Vuorinen, M. and Kainulainen, P. 2009 Potential for use of Exogenous Chemical Elicitors in Disease and Insect Pest Management of Conifer Seedling Production. The Open Forest Science J. 2(1): 17 – 24
doi: 10.2174/1874398600902010017
Honig, M., Roeber, V. M., Schmulling, T. and Cortleven, A. 2023 Chemical Priming of Plant Defense Responses to Pathogen Attacks. Front. Plant Sci. 14: 1146577
doi: 10.3389/fpls.2023.1146577
Jung, H. W., Tschaplinski, T. J., Wang, L., Glazebrook, J. and Greenberg, J. T. 2009 Priming in Systemic Plant Immunity. Science 324(5923): 89 – 91
doi: 10.1126/science.1170025
Katz, V. A., Thulke, O. U. and Conarth, U. 1998 A Benzothiadiazole Primes Parsley Cells for Augmented Elicitation of Defense Response. Plant Physiol. 117(4): 1333 – 1339
doi: 10.1104/pp.117.4.1333
Mauch-Mani, B., Baccelli, I., Luna, E. and Flors, V. 2017 Defense Priming: An Adaptive Part of Induced Resistance. Annu. Rev. Plant Biol. 68: 485 – 512
doi: 10.1146/annurev-arplant-042916-041132
Navarova, H., Bernsdorff, F., Doring, A-C. and Zeier, J. 2012 Pipecolic Acid an Endogenous Mediator of Defense Amplification and Priming is a Critical Regulator of Inducible Plant Immunity. The Plant Cell 24(12): 5123 – 5141
doi.org/10.1105/tpc.112.103564
Schnake, A., Hartmann, M., Schreiber, S., Malik, J., Brahmann, L., Yildiz, I., Von Dahlen, J., Rose, L. E., Schaffrath, U. and Zeier, J. 2020 Inducible Biosynthesis and Immune Function of the Systemic Acquired Resistance Inducer N-Hydroxypipecolic Acid in Monocotyledonous and Dicotyledonous Plants. J. Exp. Bot. 71(20): 6444 – 6459
doi.org/10.1093/jxb/eraa317
Vicedo, B., Flors, V., de la O Leyva, M., Finiti, I., Kravchuk, Z., Real, M. D., Garcia-Agustin, P. and Gonzalez-Bosch, C. 2009 Hexanoic Acid-Induced Resistance against Botrytis cinerea inTomato Plants. MPMI 22(11): 1455 – 1465
doi.org/10.1094/MPMI-22-11-1455
Vlot, A. C., Dempsey, D’M. A. and Klessig, D. F. 2009 Salicylic Acid a Multifaceted Hormone to Combat Disease. Annu. Rev. Phytopathol. 47: 177 – 206
doi.org/10.1146/annurev.phyto.050908.135202
Vogel-Adghough, D., Stahl, E., Navarova, H. and Zeier, J. 2013 Pipecolic Acid Enhances Resistance to Bacterial Infection and Primes Salicylic Acid and Nicotine Accumulation in Tobacco. Plant Signaling Behav. 8(11): e26366
doi.org/10.4161/psb.26366
Yang, Z., Zhi, P. and Chang, C. 2022 Priming Seeds for the Future: Plant Immune Memory and Application in Crop Protection. Front. Plant Sci. 13: 961840
doi: 10.3389/fpls.2022.961840
Yu, K., Soares, J. M., Mandal, M. K., Wang, C., Chanda, B., Gifford, A. N., Fowler, J. S., Navarre, D., Kachroo, A. and Kachroo, P. 2013 A Feedback, Regulatory Loop between G3P and Lipid Transfer Proteins DIR1 and AZI1 Mediates Azelaic-Acid-Induced Systemic Immunity. Cell Reports 3(4): 1266 – 1278
doi.org/10.1016/j.celrep.2013.03.030
Zimmerli, L., Jakab, G., Metraux, J. P. and Mauch-Mani, B. 2000 Potentiation of Pathogen-Specific Defense Mechanisms in Arabidopsis by b-aminobutyric Acid. PNAS USA 97(23): 12920 – 12925
doi: 10.1073/pnas.230416897
BIOLOGICAL PROCESSES- A NATURE'S GIFT 