Abstract
Some alternative control strategies of currently emerging plant diseases are based on the use of resistance inducers. This review highlights the recent advances made in the characterization of natural compounds that induce resistance by a priming mechanism. These include vitamins, chitosans, oligogalacturonides, volatile organic compounds, azelaic and pipecolic acid, among others. Overall, other than providing novel disease control strategies that meet environmental regulations, natural priming agents are valuable tools to help unravel the complex mechanisms underlying the induced resistance (IR) phenomenon. The data presented in this review reflect the novel contributions made from studying these natural plant inducers, with special emphasis placed on hexanoic acid (Hx), proposed herein as a model tool for this research field. Hx is a potent natural priming agent of proven efficiency in a wide range of host plants and pathogens. It can early activate broad-spectrum defenses by inducing callose deposition and the salicylic acid (SA) and jasmonic acid (JA) pathways. Later it can prime pathogen-specific responses according to the pathogen’s lifestyle. Interestingly, Hx primes redox-related genes to produce an anti-oxidant protective effect, which might be critical for limiting the infection of necrotrophs. Our Hx-IR findings also strongly suggest that it is an attractive tool for the molecular characterization of the plant alarmed state, with the added advantage of it being a natural compound.
Highlights
Reviewed by: Vasileios Fotopoulos, Cyprus University of Technology, Cyprus Albor Dobon Alonso, John Innes Centre, UK
The data presented in this review reflect the novel contributions made from studying these natural plant inducers, with special emphasis placed on hexanoic acid (Hx), proposed as a model tool for this research field
Hx-induced resistance (IR) against Botrytis cinerea seems to be independent of abscisic acid (ABA) production in Arabidopsis since the mutant partially impaired in ABA synthesis npq2-1 (Niyogi et al, 1998) was fully protected by Hx (Kravchuk et al, 2011). All these results indicate that Hx priming against Botrytis cinerea is based on jasmonic acid (JA)- and other oxylipin-related defenses in both tomato and Arabidopsis by activating additional responses in each background
Summary
By the transgenerational priming phenomenon when the progeny of primed plants shows an enhanced defense response (Luna and Ton, 2012). The analysis of tomato genes induced in response to Botrytis showed that, consistently with metabolic changes, Hx pre-treatment significantly primes LoxD, a LOX involved in the oxylipins pathway leading to OPDA and JA synthesis (Cohn and Martin, 2005; Flors et al, 2007). The microarray gene expression profile of Hx-treated plants revealed the induction and priming of many Botrytis-induced genes (Finiti et al, 2014) This means that Hx preventively activates these genes, preparing plants for an alarmed state, which would facilitate a quicker, better response against pathogen attack. Other natural priming agents which promotes defense response like thiamine, riboflavin, MSB, VOCs, OGs, and chitosan affect the oxidative balance contributing to reduce the symptoms and damages associated to biotic stresses (Table 1). ET* SAR Defense Cell wall Oxidative Reference oxilipins effectors tightening balance
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