Ethylene-auxin interaction and its influence on the production of aroma volatile compounds during tomato (Solanum lycopersicum) fruit ripening

Abstract

Fruit ripening is a complex and genetically programmed process through the fruit acquires characteristics (sweetness and acidity, color, softening, flavor and aroma, etc.) that make it attractive to consumers. The tomato fruit (Solanum lycopersicum) has been widely used as a model for studies on fruit ripening due to its nutritional and economic importance and advances in the understanding of its genetics and biochemistry. A set of 20 to 30 volatile substances, including alcohols, aldehydes, ketones and esters, which were derived from amino acids, fatty acids and carotenoids, contribute to the flavor. The hormone ethylene is closely related to the metabolic changes that occur in the maturation, including the generation of these volatile compounds, through the activation of transcription factors that regulate genes encoding proteins involved in this process.Although the knowledge about the biochemistry pathways that produces flavor compounds and the involvement of ethylene have advanced, little is known about the regulation of this process. In addition, ethylene is not the unique hormone that plays this role on fruit ripening. There is a growing body of evidence indicating the involvement of auxin in the maturation, either directly, through the stimulation or inhibition of expression of a set of genes auxin-dependent or indirectly, by changing the number of ethylene receptors expressed in the tissue. The role of other hormonal classes is still little explored when compared to progress made on the role of ethylene in fruit ripening, especially regarding the regulation of the biosynthetic pathways of volatile compounds.This study aim to assess how the interaction between the indole-3-acetic acid (IAA), the most abundant auxin in plants, and ethylene influence the production of tomato fruit aroma. To do this, fruit from tomato cultivar Micro-Tom will be treated with IAA and 1-aminocyclopropane carboxylic acid (the ethylene precursor, ACC), separately and in combination, as well as inhibitors of signaling for both hormones (p-chlorophenoxy-isobutyric and 1-methylcyclopropene, respectively). The application of hormones and inhibitors will be performed by injecting solutions of the substances in a model of studies developed in the laboratory of Chemistry, Biochemistry and Molecular Biology Food (FCF/USP). In addition to the levels of volatile compounds produced during ripening, it will also be evaluated transcript levels of genes encoding key enzymes of these pathways, namely lipoxygenase C (LOXC), hydroperoxide lyase (HPL) and alcohol dehydrogenase 2 (ADH2). Other genes may be incorporated into the proposal depending on the results obtained. Ethylene levels and IAA will also be evaluated in order to correlate any changes in production profiles of these hormones with changes in gene expression and also with changes in the pattern of volatile production.This project is part of a larger proposal that aims to evaluate which plant hormones are linked to the production of aroma, both in climacteric fruits (tomato and papaya) and non-climacteric fruits (strawberry and raspberry).In terms of basic research, with this proposal to be developed on tomato fruit, we hope to obtain a set of data that will contribute to the characterization of the involvement of auxin as a regulator of fruit ripening, in interaction with ethylene. Previous work of the group together with the other teams, has demonstrated that auxins are involved in regulating other processes of maturation, like, starch metabolism, pigments synthesis and modifications of the cell wall.