Abstract
Leafy gall is a plant hyperplasia induced upon Rhodococcus fascians infection. Previously, by genomic and transcriptomic analysis, it has been reported that, at the early stage of symptom development, both primary and secondary metabolisms are modified. The present study is based on the hypothesis that fully developed leafy gall, could represent a potential source of new bioactive compounds. Therefore, non-targeted metabolomic analysis of aqueous and chloroform extracts of leafy gall and non-infected tobacco was carried out by 1H-NMR coupled to principal component analysis (PCA) and orthogonal projections to latent structures-discriminant analysis (OPLS-DA). Polar metabolite profiling reflects modifications mainly in the primary metabolites and in some polyphenolics. In contrast, main modifications occurring in non-polar metabolites concern secondary metabolites, and gas chromatography and mass spectrometry (GC-MS) evidenced alterations in diterpenoids family. Analysis of crude extracts of leafy galls and non-infected tobacco leaves exhibited a distinct antiproliferative activity against all four tested human cancer cell lines. A bio-guided fractionation of chloroformic crude extract yield to semi-purified fractions, which inhibited proliferation of glioblastoma U373 cells with IC50 between 14.0 and 2.4 μg/mL. Discussion is focused on the consequence of these metabolic changes, with respect to plant defense mechanisms following infection. Considering the promising role of diterpenoid family as bioactive compounds, leafy gall may rather be a propitious source for drug discovery.
Highlights
Plant galls are tumors triggered by external aggressions, especially microorganisms or insects [1]. galls display many phenotypes, they provide niches to protect and ensure the survival of the pathogen [2,3]
The metabolic changes characterizing the fully developed leafy gall, which is the ecological niche of the R. fascians, remain largely unexplored, except for the identification of 7-methyl-esculin, a phenolic compound accumulated in tobacco symptomatic tissues, but not in non-infected tissues [13]
Tobacco plants 11 weeks post germination and a typical eight-week-old Leafy galls (LG), a morphological structure with multiple dormant buds and malformed leaves characterized by increased trichomes formations
Summary
Plant galls are tumors triggered by external aggressions, especially microorganisms or insects [1]. galls display many phenotypes, they provide niches to protect and ensure the survival of the pathogen [2,3]. Rhodococcus fascians, a phytopathogenic soil Gram-positive actinomycete has been shown to produce phytohormones [5,9,10], triggering plant cell divisions and signal transduction. This leads to cell reprogramming [11,12], resulting in the development of the so-called leafy galls on a wide range of host plants [8]. The metabolic changes characterizing the fully developed leafy gall, which is the ecological niche of the R. fascians, remain largely unexplored, except for the identification of 7-methyl-esculin, a phenolic compound accumulated in tobacco symptomatic tissues, but not in non-infected tissues [13]
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