A multidisciplinary approach to elucidate glandular trichome differentiation in tomato

• Applicant: Professor Dr. Alain Tissier
• Subject Area: Plant Cell and Developmental Biology ; Plant Biochemistry and Biophysics ; Plant Genetics and Genomics
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 238047333

Glandular trichomes are structures located on the surface of the aerial parts of plants which are able to produce, secrete and, in some cases, store metabolites. The metabolites they produce are often species-, sometimes even accession-, specific, and they have been shown to play diverse roles in the protection against pests, particularly insects. In the tomato clade, wild relatives of the cultivated tomato produce a diverse array of metabolites in their glandular trichomes, including sesquiterpene carboxylic acids, methyl ketones or acyl sugars. Because these wild relatives can be crossed to S. lycopersicum, the introgression of these trichome traits into the cultivated tomato can be envisaged to confer durable resistance to insects. Several types of glandular trichomes occur in tomato, but the type VI trichomes appear to be the most abundant and the most important contributors of leaf secretions. In preliminary experiments, we showed that type VI trichomes in S. habrochaites differ from those of S. lycopersicum in that they contain an intercellular cavity which constitutes a reservoir for the accumulation of secretory products. Because the quantity of trichome products is an important factor to resistance, it is essential to understand the molecular basis of the formation of this intercellular cavity to introduce trichome-borne traits into cultivated tomato. By immuno-staining we could show that pectin demethylation and lysis may play a critical role in the formation of this cavity. Furthermore, we could develop a quantitative phenotyping for type VI trichome shape, allowing us to clearly distinguish type VI trichomes of the cultivated and wild species. This quantitative phenotyping was used to characterize a back-cross population (75 individuals) between S. habrochaites LA1777 and S. lycopersicum WVA106. This showed a continuous distribution between the parental phenotypes providing the basis for quantitative genetics. In this project, we aim to identify genes and molecular markers underlying this type VI trichome phenotype. This will be carried out by two main approaches. The first relies on a combination of comparative biochemical and transcriptomic analyses. This will result in a set of candidate genes which will be functionally characterized in planta. The second approach will be based on our extended back-cross population for QTL mapping. The tomato genome sequence should considerably facilitate the identification of genome intervals containing the QTL and of putative candidate genes. Both approaches are complementary and could converge on genes of interest. In addition to molecular markers for breeding insect-resistant tomato, this project should also further our knowledge of basic processes pertaining to cell separation and metabolite storage in plants.

• DFG Programme: Research Grants
• Participating Persons: Dr. José M. Jiménez-Gómez; Professor Dr. Albrecht E. Melchinger