Foliar treatments with Gaultheria procumbens essential oil induce defense responses and resistance against a fungal pathogen in Arabidopsis.

Sophie Vergnes,Faouzi Attia,Bernard Dumas,Sylvie Fournier,Nathalie Ladouce,Hicham Ferhout

doi:10.3389/fpls.2014.00477

Abstract

Essential oil from Gaultheria procumbens is mainly composed of methylsalicylate (MeSA) (>96%), a compound which can be metabolized in plant tissues to salicylic acid, a phytohormone inducing plant immunity against microbial pathogens. The potential use of G. procumbens essential oil as a biocontrol agent was evaluated on the model plant Arabidopsis thaliana. Expression of a selection of defense genes was detected 1, 6, and 24 h after essential oil treatment (0.1 ml/L) using a high-throughput qPCR-based microfluidic technology. Control treatments included methyl jasmonate and a commercialized salicylic acid (SA) analog, benzo(1,2,3)-thiadiazole-7carbothiolic acid (BTH). Strong induction of defense markers known to be regulated by the SA pathway was observed after the treatment with G. procumbens essential oil. Treatment induced the accumulation of total SA in the wild-type Arabidopsis line Col-0 and analysis of the Arabidopsis line sid2, mutated in a SA biosynthetic gene, revealed that approximately 30% of MeSA sprayed on the leaves penetrated inside plant tissues and was demethylated by endogenous esterases. Induction of plant resistance by G. procumbens essential oil was tested following inoculation with a GFP-expressing strain of the Arabidopsis fungal pathogen Colletotrichum higginsianum. Fluorescence measurement of infected tissues revealed that treatments led to a strong reduction (60%) of pathogen development and that the efficacy of the G. procumbens essential oil was similar to the commercial product BION®. Together, these results show that the G. procubens essential oil is a natural source of MeSA which can be formulated to develop new biocontrol products.

Highlights

Plant are constantly challenged by harmful microorganisms and diseases caused by fungal, bacterial, or viral phytopathogens pose severe threats to crop productivity worldwide (Fisher et al, 2012)
INDUCTION OF GENE EXPRESSION UPON Gaultheria essential oil (GEO) TREATMENTS To construct a diagnostic chip to monitor plant defense responses, marker genes corresponding to various classes of immune responses were selected by mining transcriptomic databases (Winter et al, 2007; Hruz et al, 2008) and bibliographic data (Table S2)
To validate the selection of marker genes, Arabidopsis plants (Col-0) grown in microtiter plates were treated with solutions containing mehyljasmonate (MeJA), FLG22 peptide, BTH (BION® formulation), and chitosaccharidic fragments obtain from crab shell chitin (DP 6-9) (Nars et al, 2013)

Summary

Introduction

Plant are constantly challenged by harmful microorganisms and diseases caused by fungal, bacterial, or viral phytopathogens pose severe threats to crop productivity worldwide (Fisher et al, 2012). Controlling plant diseases requires the use of massive amounts of synthetic pesticides, the breeding of resistant plant varieties, and agronomical strategies such as crop rotation. The development of an environmental-friendly and sustainable agriculture drives the search for alternative strategies and among these the use of natural compounds able to stimulate the plant immune system. The first line of microbial perception occurs through the detection of molecular patterns exposed or released by microbial molecules and named PAMPs (or MAMPs; Pathogen (or Microbial) Associated Molecular Patterns). These molecular patterns interact with specialized receptors and the perception of PAMPs induced a signaling cascade which culminates with the expression of defense genes (Boller and Felix, 2009)

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