Genome-wide identification and characterization of genes involved in the acylsugar pathway in tomato

Acylsugars are allelochemicals secreted by type IV trichomes in leaves and have been associated with resistance to arthropod pests in Solanaceae species. Eighty-seven putative genes were identified in Solanum lycopersicum and 77 in Solanum pennellii involved in the acylsugar pathway, including genes coding key proteins branched-chain keto acid dehydrogenase E2 (BCKD E2), 2-isopropylmalate synthase A (IPMSA), and threonine deaminase/ dehydratase (TD). These putative tomato proteins displayed conservation in the conserved domains distribution and amino acids presence of catalytically active site comparing to homologous BCKD E2, IPMSA, and TD proteins from the acylsugar pathway. Phylogenetic analysis of the putative proteins BCKD E2, IPMSA, and TD showed that all putative tomato proteins grouped with their orthologs from the Solanaceae species, corroborating with the distribution of the tree of life. The BCKD E2 and the IPMSA transcripts from S. pennellii showed higher gene expression compared to S. lycopersicum transcripts, suggesting that the acylsugar pathway is more active in wild than in cultivated tomato. In addition, we checked the expression of these genes at three different times (30, 60 and 90 days after planting). The 60-day plants showed higher expression of these genes than the 30- and 90-day plants, which indicates a greater production of metabolites in the flowering stage and suggests that at this development stage the plant demands more defense against pests that may be attracted by flowers. Given the important role of the allelochemicals produced in Solanaceae, the results contribute to a better understanding of acylsugars and their processing pathways and open up opportunities to study their relationship with biotic resistance in these important species and other Solanaceae species.