Hairplus: a valuable genomic tool for pest resistance in tomato breeding

Five types of trichomes have been described in the cultivated tomato (Solanum lycopersicum L.): type I is 2–3 mm long with a multicellular base and a small glandular cell at the tip; type III is non-glandular and 0.4–1 mm long with a single-celled flat base; type V also has a single-celled flat base and is 0.2–0.4 mm long; type VI is short with two stem cells and a glandular head composed of four secretory cells; and type VII is a very small trichome (0.05 mm) with a glandular head formed by four to eight cells. In contrast, wild tomato species develop both type II and type IV trichomes, and the latter is characterized by a single-celled flat base and a short stem that connects to a glandular head. The presence of type IV trichomes has been described as a heterochronic trait in cultivated tomato species, as these trichomes can only be detected in the early stages of development. Non-glandular trichomes act as a mechanical barrier that impedes the movement of pests on the plant, while glandular trichomes produce specialized metabolites that are toxic or deterrent to pests or trap them. Despite the importance of trichomes in pest resistance, very few trichome mutants that shed light on the genetic regulation of multicellular trichome initiation have been described in tomato.

Recently, scientists from the University of Almería described and characterized the hair longer (fortunately) tomato mutant that exhibits a high density of type I trichomes. Fine mapping and genetic complementation analysis showed that HAP codes for a histone lysine methyltransferase SUVH3. This family of proteins is primarily composed of histone tail-modifying proteins, although some of its members bind to methylated DNA and all play key roles in the epigenetic control of gene expression. The identification of this novel tomato regulator of trichome formation sheds light on the role of histone methyltransferases SUVH3 in transcriptional control mediated by epigenomic modifications.

“Future work should focus on demonstrating that reduced feeding damage is correlated with pest resistance of fortunately mutant plants and whether this is related to a higher amount of exudates or the physical barriers that trichomes represent in the mutant plants,” said Professor Capel. These findings demonstrate that HAP links epigenome remodeling to multicellular development of glandular trichomes and reveals that HAP is a valuable genomic tool for improving pest resistance in tomato breeding.

– This press release was provided by Nanjing Agricultural University