Editorial: Physiology and Cellular Mechanisms of Isothiocyanates and Other Glucosinolate Degradation Products in Plants

The isothiocyanate sulforaphane induces respiratory burst oxidase homologue D-dependent reactive oxygen species production and regulates expression of stress response genes

Sulforaphane (SFN) is an isothiocyanate-type phytomolecule present in crucifers, which is mainly synthesized in response to biotic stress. In animals, SFN incorporated in the diet has anticancer properties among others. The mechanism of action and signaling are well described in animals; however, little is known in plants. The goal in the present study is to elucidate components of the SFN signaling pathway, particularly the production of reactive oxygen species (ROS), and its effect on the transcriptome. Our results showed that in Arabidopsis, SFN causes ROS production exclusively through the action of the NADPH oxidase RBOH isoform D that requires calcium as a signaling component for the ROS production. To add to this, we also analyzed the effect of SFN on the transcriptome by RNAseq. We observed the highest expression increase for heat shock proteins (HSP) genes and also for genes associated with the response to oxidative stress. The upregulation of several genes linked to the biotic stress response confirms the interplay between SFN and this stress. In addition, SFN increases the levels of transcripts related to the response to abiotic stress, as well as phytohormones. Taken together, these results indicate that SFN induces an oxidative burst leading to signaling events. This oxidative burst may cause the increase of the expression of genes such as heat shock proteins to restore cellular homeostasis and genes that codify possible components of the signaling pathway and putative effectors.

Plant Bioactive Compounds in Pre- and Postharvest Management for Aflatoxins Reduction

Aflatoxins (AFs) are secondary metabolites produced by Aspergillus spp., known for their hepatotoxic, carcinogenic, and mutagenic activity in humans and animals. AF contamination of staple food commodities is a global concern due to their toxicity and the economic losses they cause. Different strategies have been applied to reduce fungal contamination and AF production. Among them, the use of natural, plant-derived compounds is emerging as a promising strategy to be applied to control both Aspergillus spoilage and AF contamination in food and feed commodities in an integrated pre- and postharvest management. In particular, phenols, aldehydes, and terpenes extracted from medicinal plants, spices, or fruits have been studied in depth. They can be easily extracted, they are generally recognized as safe (GRAS), and they are food-grade and act through a wide variety of mechanisms. This review investigated the main compounds with antifungal and anti-aflatoxigenic activity, also elucidating their physiological role and the different modes of action and synergies. Plant bioactive compounds are shown to be effective in modulating Aspergillus spp. contamination and AF production both in vitro and in vivo. Therefore, their application in pre- and postharvest management could represent an important tool to control aflatoxigenic fungi and to reduce AF contamination.

Mutations in the Arabidopsis ROL17/isopropylmalate synthase 1 locus alter amino acid content, modify the TOR network, and suppress the root hair cell development mutant lrx1

The growth and development of organisms must be tightly controlled and adjusted to nutrient availability and metabolic activities. The Target of Rapamycin (TOR) network is a major control mechanism in eukaryotes and influences processes such as translation, mitochondrial activity, production of reactive oxygen species, and the cytoskeleton. In Arabidopsis thaliana, inhibition of the TOR kinase causes changes in cell wall architecture and suppression of phenotypic defects of the cell wall formation mutant lrx1 (leucine-rich repeat extensin 1). The rol17 (repressor of lrx1 17) mutant was identified as a new suppressor of lrx1 that induces also a short root phenotype. The ROL17 locus encodes isopropylmalate synthase 1, a protein involved in leucine biosynthesis. Dependent on growth conditions, mutations in ROL17 do not necessarily alter the level of leucine, but always cause development of the rol17 mutant phenotypes, suggesting that the mutation does not only influence leucine biosynthesis. Changes in the metabolome of rol17 mutants are also found in plants with inhibited TOR kinase activity. Furthermore, rol17 mutants show reduced sensitivity to the TOR kinase inhibitor AZD-8055, indicating a modified TOR network. Together, these data suggest that suppression of lrx1 by rol17 is the result of an alteration of the TOR network.

Bis (Isothiocyanatomethyl) Benzene, A Plant Derived Anti-Neoplastic Compound: Purified from Moringa Oleifera Leaf Extract

BACKGROUND

Moringa oleifera lam, commonly known as "Sajina", is an indigenous species to India. In our folk medicine, it is used for the treatment of Canker (cancer). The Moringa oleifera leaf extract contains many phyto-compounds, with some being anti-neoplastic in nature.

OBJECTIVE

Our preliminary study showed that the leaf extract significantly kills cancer cells compared to normal cells. On searching for the new phyto-compound, Bis-isothiocyanatomethyl) benzene was purified and isolated.

METHODS

The sequential process of fractional distillation, column chromatography, followed by TLC and HPLC is performed for purification. Every fraction from each step was tested on HeLa cell line for evaluating the presence of the phyto-compound.

RESULTS AND CONCLUSION

FTIR peak analysis of a single phyto-compound shows the presence of thiocyanate group, aromatic carbon group. 1H & 13C NMR peak analysis along with High-resolution mass spectroscopy (HRMS) calculation confirm the chemical structure with IUPAC name [Bis (Isothiocyanatomethyl) benzene]. Previously, Isothiocyanatomethyl- benzene solely or in conjugation with sugar molecule has been reported, but its dimeric form in nature hasnot yet been published anywhere. It shows anticancer activity by retarding cancer cell growth & inhibits carcinogenesis on HeLa, MCF-7, and MDA-MB-231 cell lines by caspase 3 apoptotic pathway and showed comparatively less cytotoxicity to PBMC cell. It shows anticancer activity almost the same as the market available drug Cis-Platin. Therefore, further extrapolating its activity with different concentrations may result in its use as a drug formulation for the treatment of cancer.

Effect of heat root stress and high salinity on glucosinolates metabolism in wild rocket

Wild rocket (Diplotaxis tenuifolia L.) is a leafy vegetable appreciated for its characteristic sensory properties which are mainly due to the presence of glucosinolates (GSLs). Short-term exposure to abiotic stresses can induce physiological responses and transcriptional changes which involve GSLs. For this reason, the aim of this work was to study the mechanisms of regulation of GSLs metabolism in rocket subjected to heat stress (40 °C) and high salinity (200 mM NaCl) imposed for up to 48 h. GSLs levels and the expression of methylthioalkylmalate synthase1 (DtMAM1), cytochromeP79F1 (DtCYP79F1), cytochromeP45083A1 (DtCYP83A1), cytosolic-sulfotransferase5b (DtST5b), cytosolic-sulfotransferase5c (DtST5c), flavinmono-oxygenase (DtFMO), myrosinase (DtMyro) and thio-methyl transferase (DtTMT) were analyzed under stress conditions. In addition, the effect on chlorophyll and glucose levels, as well as on chlorophyll a fluorescence were evaluated. Chlorophyll and chlorophyll fluorescence were not affected by the short-term application of stresses. Glucose levels in roots were doubled in response to high salinity, while, in the same organ, GSLs were three fold lower in response to both stresses. The relative content of several aliphatic GSLs was significantly reduced in leaves as a response to both stresses. A key role in GSLs metabolism and in the response to salinity is hypothesized for the gene DtTMT, as it showed an increment in transcripts accumulation (three-fold) consistent with the decrement in the GSLs levels found in salt-exposed leaves and roots. The results obtained in this study can be used in breeding programmes aiming to enhance rocket sensory quality and to improve the resistance to abiotic stresses.

Allyl-isothiocyanate treatment induces a complex transcriptional reprogramming including heat stress, oxidative stress and plant defence responses in Arabidopsis thaliana

Background

Isothiocyanates (ITCs) are degradation products of the plant secondary metabolites glucosinolates (GSLs) and are known to affect human health as well as plant herbivores and pathogens. To investigate the processes engaged in plants upon exposure to isothiocyanate we performed a genome scale transcriptional profiling of Arabidopsis thaliana at different time points in response to an exogenous treatment with allyl-isothiocyanate.

Results

The treatment triggered a substantial response with the expression of 431 genes affected (P < 0.05 and log₂ ≥ 1 or ≤ -1) already after 30 min and that of 3915 genes affected after 9 h of exposure, most of the affected genes being upregulated. These are involved in a considerable number of different biological processes, some of which are described in detail: glucosinolate metabolism, sulphate uptake and assimilation, heat stress response, oxidative stress response, elicitor perception, plant defence and cell death mechanisms.

Conclusion

Exposure of Arabidopsis thaliana to vapours of allyl-isothiocyanate triggered a rapid and substantial transcriptional response affecting numerous biological processes. These include multiple stress stimuli such as heat stress response and oxidative stress response, cell death and sulphur secondary defence metabolism. Hence, effects of isothiocyanates on plants previously reported in the literature were found to be regulated at the gene expression level. This opens some avenues for further investigations to decipher the molecular mechanisms underlying the effects of isothiocyanates on plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3039-x) contains supplementary material, which is available to authorized users.