BARD - understanding and improving quality traits in fruit: genetic manipulation of the tomato fruit cuticle

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The skin of fleshy fruits consists of a layer of epidermal cells that are covered with a thick waxy cuticle. The latter is crucial for resistance against pathogens and drought, and for the appearance of the fruit (color, glossiness, texture), the efficacy of post harvest treatments, storage, transport and shelf life. Therefore, it is a very important factor determining fruit quality and, consequently, customer preference. To improve fruit quality, cuticle structure and composition must be altered so that certain cuticle traits are enhanced without impeding its essential functions. This goal can only be reached based on a thorough understanding of the genetic regulation of the various biosynthetic pathways involved in cuticle formation. Previous studies either focused on fruit flesh, ignoring the importance of the skin, or specialized in narrowly selected compositional elements of the fruit cuticle. In this project we propose to investigate all four important biosynthetic pathways relevant for tomato fruit cuticle formation (wax, cutin, triterpenoid and flavonoid biosynthesis).      The objectives of this project are: a) to generate a molecular tool box for manipulating the tomato fruit skin by isolating epidermis-specific genes and promoters involved in key steps of the four pathways; b) to generate transgenic plants overexpressing or RNAi silenced in genes isolated in objective a; c) to phenotypically characterize the transgenics with respect to fruit cuticle ultrastructure and composition; d) to assess the resulting fruit quality of transgenic lines by measuring water potential, transpiration, cracking resistance, growth and shelf life; e) to generate crosses between transgenic lines altered in the different cuticle metabolic pathways in order to test the combined effect of various components on skin properties and fruit traits.      The project is a newly established collaboration of three labs, combining expertise in fruit molecular genetics, phytochemistry, physiology and fruit quality assessment. It will provide fundamental knowledge on fruit skin structure and properties. Moreover, it will assist in the future selection of tomato breeding lines and the generation of transgenic lines with fruit having optimal skin properties and therefore enhanced quality.