Study of MicroTom-PIC introgression effect on trichome development and terpenoid production

Glandular trichomes can accumulate and release defensive compounds against herbivorous pests. In the wild tomato Solanum habrochaites, the gland of type-VI trichomes have a profoundly round-shape, differing from the more mushroom-shaped trichome present on cultivated tomatoes. The gland size of the wild species has been associated with high levels of natural insecticides that are accumulated in its intercellular cavity. By contrast, type-VI trichome glands of the cultivated tomato produce low levels of non-toxic compounds, making cultivated tomatoes less resistant to insect pests. For this reason, the transfer of the genetic determinants of the wild species type-VI trichome morphology and functionality to cultivated tomato is of great interest. A near-isogenic line carrying a wild-ancestor introgression in the background of S. lycopersicum c.v. Micro-Tom was named MT-Pincushion (MT-Pic) after the shape of its trichomes. MT-Pic appears to carry alleles contributing to the morphology of type-VI trichomes as seen in the S. habrochaites parental. Using genotyping by sequencing (GBS) we narrowed down the region of the Pic introgression. By additional transfer of the plastidial-sesquiterpene locus from S. habrochaites PI127826 to the type-VI trichomes of the MT-Pic line we showed that the introgression of the Pic-locus allows for higher accumulation of anti-insect sesquiterpenes. Using trichome RNAseq data, we narrow down the list of putative genes involved in type-VI trichomes morphology. This work paves the way for the understanding of the genetic factors underlying the morphology and functionality of type-VI trichomes, towards breeding for insect-resistant tomatoes.