Glandless, a tomato HD-ZIP transcription factor, is important for the gland formation of type VI trichomes

Tomato (Solanum lycopersicum) is a model plant to study glandular trichome development and their specialized metabolism, and several transcription factors (TF) regulating these intertwined traits and their network have been functionally characterized. Among them are members of the homeodomain leucine zipper subfamily IV (HD-ZIP IV). Here, we study a tomato EMS-mutant line, glandless, presenting mutant, glandless type VI trichomes with a consequential reduction in volatile terpene levels. This mutant trichome also has some morphological characteristics of a type IV trichome. The glandless mutant has altered trichome densities, and acylsugar biosynthesis is slightly increased. As verified via virus-induced gene silencing (VIGS), the gene underlying this phenotype is SlHDZ38, the first member of HD-ZIP subfamily I found to regulate the development and specialized metabolism of glandular trichomes. Additionally, we show that the expression of an intricate network of known trichome-related regulatory TFs and biosynthetic enzymes is affected by the glandless mutation. Overall, our results contribute to the elucidation of the network of TFs controlling tomato trichomes.