ASTF1, an AP2/ERF-family transcription factor and ortholog of cultivated tomato LEAFLESS, is required for acylsugar biosynthesis

Abstract

Acylsugars, specialized metabolites produced by solanaceous trichomes, provide protection against biotic and abiotic stresses. Here, we report ACYLSUGAR TRANSCRIPTION FACTOR1 (ASTF1/Sopen05g008450; AP2/ERF-family member) positively regulates acylsugar biosynthesis. Virus-induced gene silencing (VIGS) of ASTF1 in Solanum pennellii reduced acylsugar production by 65%. Most acylsugar (and several flavonoid) metabolic genes were downregulated in ASTF1-silenced plants, and these genes showed strong co-expression with ASTF1. In promoters of potential ASTF1-targets, we identified three enriched motifs, and one motif showed similarity with binding sites of other AP2/ERFs. Phylogenetic analysis and data mining indicated trichome-enriched expression of ASTF1 orthologs in several acylsugar-producing solanaceous species, suggesting a conserved role in acylsugar biosynthesis. This was supported by VIGS of ASTF1 orthologs in Nicotiana benthamiana. Broader phylogenetic analysis revealed relationships among specialized metabolic AP2/ERFs in several asterid species and provided clues about evolutionary emergence of acylsugar phenotype. Cultivated tomato ortholog (LEAFLESS/Solyc05g013540) has been reported to coordinate leaf initiation with transient expression at incipient primordia, and data mining revealed downregulation of trichome-preferentially-expressed genes, including acylsugar (and flavonoid) metabolic genes, in leafless mutants' shoot apices, indicating remarkable spatiotemporal functional diversity. Our work will pave a way to disentangle acylsugar regulatory network and holds promise for future metabolic engineering of acylsugar production.