Role of LEAFLESS, an AP2/ERF family transcription factor, in the regulation of trichome specialized metabolism

Acylsugars, specialized metabolites produced by trichomes of many solanaceous species, provide protection against biotic and abiotic stresses. Many acylsugar metabolic enzymes have been identified; however, regulatory factors remain unknown. Our multidisciplinary approaches identified LEAFLESS (APETALA 2/ ETHYLENE RESPONSE FACTOR (AP2/ERF) family member) as a positive regulator of acylsugar biosynthesis. Virus-induced gene silencing (VIGS) of LEAFLESS in Solanum pennellii (SpLFS/Sopen05g008450) revealed its distinct roles in two related but separate processes: acylsugar biosynthesis and trichome development. Most acylsugar (and several flavonoid) metabolic genes were downregulated in SpLFS-silenced plants and showed strong co-expression with SpLFS. Phylogenetic and additional data analyses indicated trichome-enriched expression of SpLFS orthologs in other acylsugar-producing solanaceous species, and VIGS of SpLFS orthologs in Nicotiana benthamiana reduced acylsugar production. Transcriptional reporter showed expression of SpLFS in type I/IV trichome tip cells, the site of acylsugar biosynthesis. Electrophoretic mobility shift assays indicated that SpLFS directly binds to promoters of several acylsugar (and flavonoid) metabolic genes. Additionally, data mining suggested remarkable spatiotemporal functional diversity: from coordinating leaf initiation at incipient primordia (previously reported for the S. lycopersicum ortholog SlLFS/Solyc05g013540) to regulating trichome specialized metabolism (acylsugar and flavonoid). Our work highlights a critical role of LEAFLESS in trichome specialized metabolism, paving the way to disentangle the acylsugar regulatory network.