Abstract
Immune-stimulated plants are able to respond more rapidly and adequately to various biotic stresses allowing them to efficiently combat an infection. During the priming phase, plant are stimulated in absence of a challenge, and can accumulate and store conjugates or precursors of molecules as well as other compounds that play a role in defense. These molecules can be released during the defensive phase following stress. These metabolites can also participate in the first stages of the stress perception. Here, we report the metabolic changes occuring in primed plants during the priming phase. β-aminobutyric acid (BABA) causes a boost of the primary metabolism through the tricarboxylic acids (TCA) such as citrate, fumarate, (S)-malate and 2-oxoglutarate, and the potentiation of phenylpropanoid biosynthesis and the octodecanoic pathway. On the contrary, Pseudomonas syringae pv tomato (PstAvrRpt2) represses the same pathways. Both systems used to prime plants share some common signals like the changes in the synthesis of amino acids and the production of SA and its glycosides, as well as IAA. Interestingly, a product of the purine catabolism, xanthosine, was found to accumulate following both BABA- and PstAvrRpt2-treatement. The compounds that are strongly affected in this stage are called priming compounds, since their effect on the metabolism of the plant is to induce the production of primed compounds that will help to combat the stress. At the same time, additional identified metabolites suggest the possible defense pathways that plants are using to get ready for the battle.
Highlights
Plants are generally confined to one location for their whole lifetime and had to develop adaptive and defensive mechanisms against biotic and abiotic stresses that take this limitation into account
In order to differentiate between chemical and biological induction, by β-aminobutyric acid (BABA) was used as a chemical inducer (Zimmerli et al, 2000; Jakab et al, 2001; Ton and Mauch-Mani, 2004) and the avirulent bacterium Pseudomonas syringae carrying the avirulence gene AvrRpt2 (PstAvrRpt2; Mudgett and Staskawicz, 1999) as a biological inducer of resistance
Since metabolites are the final products resulting from metabolic pathways, the present work aims to identify, the main compounds that could act as signals during the priming phase and the involved pathways
Summary
Plants are generally confined to one location for their whole lifetime and had to develop adaptive and defensive mechanisms against biotic and abiotic stresses that take this limitation into account. Plants have acquired the ability to widely improve their defensive capacity against a broad range of pathogens including viruses, fungi, oomycetes, and bacteria toward which they are genetically speaking susceptible (Durrant and Dong, 2004; Hammerschmidt, 2009) This defense has to be triggered by an inducing treatment. Various such treatments have been shown to successfully induce resistance They consist among others of an inoculation with pathogens, rhizobacteria or a treatment with defined chemicals and lead to horizontal resistance of the plant against a broad range of pathogenic organisms (van Loon et al, 1998; Oostendorp et al, 2001; Cohen, 2002; Hammerschmidt, 2009). This resistance operates in all plant parts distant from the original locus of inoculation and is called systemic resistance (Durrant and Dong, 2004)
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