Secretion mechanisms of volatile organic compounds in specialized cells of aromatic plants

The present review focuses on cells secreting volatile odorant compounds. This cell type is found in a wide variety of plants, grouped under the term aromatic plants. Such secreting cells are very diverse in morphology, from highly specialized trichomes to nonspecialized cells, including the secretory epidermal cells of petals and osmophores. In these various types of cell, the biosynthetic pathways of three main groups of volatile organic compounds are recognized: isoprenoids, fatty acid derivatives and aromatic compounds. The precise cellular localization of these pathways has not yet been elucidated in all cases, though many of the enzymes involved have already been cloned. These have been found to be frequently located in plastids but also in endoplasmic reticulum or even cytosol. Two alternative mechanisms of secretion termed granulocrine and eccrine have been postulated to exist. Recent studies support the fact that both mechanisms could exist for different compounds and different plants. This review will discuss also the route by which secreted molecules make their way through the cell wall and cuticle

The fungal metabolite 4‐hydroxyphenylacetic acid from Neofusicoccum parvum modulates defence responses in grapevine

In a consequence of global warming, grapevine trunk diseases (GTDs) have become a pertinent problem to viticulture, because endophytic fungi can turn necrotrophic upon host stress killing the plant. In Neofusicoccum parvum Bt-67, plant-derived ferulic acid makes the fungus release Fusicoccin aglycone triggering plant cell death. Now, we show that the absence of ferulic acid lets the fungus secrete 4-hydroxyphenylacetic acid (4-HPA), mimicking the effect of auxins on grapevine defence and facilitating fungal spread. Using Vitis suspension cells, we dissected the mode of action of 4-HPA during defence triggered by the bacterial cell-death elicitor, harpin. Early responses (cytoskeletal remodelling and calcium influx) are inhibited, as well as the expression of Stilbene Synthase 27 and phytoalexin accumulation. In contrast to other auxins, 4-HPA quells transcripts for the auxin conjugating GRETCHEN HAGEN 3. We suggest that 4-HPA is a key component of the endophytic phase of N. parvum Bt-67 preventing host cell death. Therefore, our study paves the way to understand how GTDs regulate their latent phase for successful colonisation, before turning necrotrophic and killing the vines

Metabolic and molecular rearrangements of Sauvignon Blanc (Vitis vinifera L.) berries in response to foliar applications of specific dry yeast

Dry yeast extracts (DYE) are applied to vineyards to improve aromatic and secondary metabolic compound content and wine quality; however, systematic information on the underpinning molecular mechanisms is lacking. This work aimed to unravel, through a systematic approach, the metabolic and molecular responses of Sauvignon Blanc berries to DYE treatments. To accomplish this, DYE spraying was performed in a commercial vineyard for two consecutive years. Berries were sampled at several time points after the treatment, and grapes were analyzed for sugars, acidity, free and bound aroma precursors, amino acids, and targeted and untargeted RNA-Seq transcriptional profiles. The results obtained indicated that the DYE treatment did not interfere with the technological ripening parameters of sugars and acidity. Some aroma precursors, including cys-3MH and GSH3MH, responsible for the typical aromatic nuances of Sauvignon Blanc, were stimulated by the treatment during both vintages. The levels of amino acids and the global RNA-seq transcriptional profiles indicated that DYE spraying upregulated ROS homeostatic and thermotolerance genes, as well as ethylene and jasmonic acid biosynthetic genes, and activated abiotic and biotic stress responses. Overall, the data suggested that the DYE reduced berry oxidative stress through the regulation of specific subsets of metabolic and hormonal pathway

Recent Advances in Plant Metabolomics: From Metabolic Pathways to Health Impact

In the past decade, technological development allowed a rapid advance on several OMIC approaches, metabolomics was no exception [...

Metabolism and roles of stilbenes in plants

International audienceStilbenes are a small family of plant secondarymetabolites derived from the phenylpropanoid pathway, and produced in a number of unrelated plant species. These compounds have numerous implications in plant disease resistance and human health. This review first presents the stilbene biosynthesis pathway and recent advances in the characterization of stilbene biosynthetic genes in different plant species. A large body of evidence indicates that stilbenes participate in both constitutive and inducible defense mechanisms in plants, however, the detailed functions of these compounds have not been fully elucidated. The second part of this review discusses known functions of stilbenes in plants, especially in plant–pathogen and plant–herbivore relationships, or in plants subjected to abiotic stresses

Model Plants and Functional Genomic Approaches Applied to the Characterization ofGenes Involved in Floral Scent Biosynthesis

International audienceFlower scents have been subjected to extensive chemical characterization for many years, providing detailed analyses of the complex mixture of volatiles emitted by flowers. However, the past ten years have seen a rapid acceleration of progress in flower scent research, with the characterization of numerous genes involved in scent biosynthesis. This review focuses on the evolution of flower scent research, from the early biochemical to the present genomic approaches, illustrating how the use of different plant models, combined with functional genomic approaches, contributed to the present knowledge in this field

Genetic mechanisms underlying the methylation level of anthocyanins in grape (Vitis vinifera L.)

International audienceBackground: Plant color variation is due not only to the global pigment concentration but also to the proportion of different types of pigment. Variation in the color spectrum may arise from secondary modifications, such as hydroxylation and methylation, affecting the chromatic properties of pigments. In grapes (Vitis vinifera L.), the level of methylation modifies the stability and reactivity of anthocyanin, which directly influence the color of the berry. Anthocyanin methylation, as a complex trait, is controlled by multiple molecular factors likely to involve multiple regulatory steps. Results: In a Syrah x Grenache progeny, two QTLs were detected for variation in level of anthocyanin methylation. The first one, explaining up to 27% of variance, colocalized with a cluster of Myb-type transcription factor genes. The second one, explaining up to 20% of variance, colocalized with a cluster of O-methyltransferase coding genes (AOMT). In a collection of 32 unrelated cultivars, MybA and AOMT expression profiles correlated with the level of methylated anthocyanin. In addition, the newly characterized AOMT2 gene presented two SNPs associated with methylation level. These mutations, probably leading to a structural change of the AOMT2 protein significantly affected the enzyme specific catalytic efficiency for the 3'-O-methylation of delphinidin 3-glucoside. Conclusion: We demonstrated that variation in methylated anthocyanin accumulation is susceptible to involve both transcriptional regulation and structural variation. We report here the identification of novel AOMT variants likely to cause methylated anthocyanin variation. The integration of QTL mapping and molecular approaches enabled a better understanding of how variation in gene expression and catalytic efficiency of the resulting enzyme may influence the grape anthocyanin profile

My way: noncanonical biosynthesis pathways for plant volatiles

International audiencePlant volatiles are crucial for various interactions with other organisms and their surrounding environment. A large number of these volatiles belong to the terpenoid and benzenoid/phenylpropanoid classes, which have long been considered to be exclusively synthesized from a few canonical pathways. However, several alternative pathways producing these plant volatiles have been discovered recently. This review summarizes the current knowledge about new pathways for these two major groups of plant volatiles, which open new perspectives for applications in metabolic engineering