Abstract
Steroidal glycoalkaloids (SGAs) are cholesterol-derived molecules produced by solanaceous species. They contribute to pathogen defence but are toxic to humans and considered as anti-nutritional compounds. Here we show that GLYCOALKALOID METABOLISM 9 (GAME9), an APETALA2/Ethylene Response Factor, related to regulators of alkaloid production in tobacco and Catharanthus roseus, controls SGA biosynthesis. GAME9 knockdown and overexpression in tomato and potato alters expression of SGAs and upstream mevalonate pathway genes including the cholesterol biosynthesis gene STEROL SIDE CHAIN REDUCTASE 2 (SSR2). Levels of SGAs, C24-alkylsterols and the upstream mevalonate and cholesterol pathways intermediates are modified in these plants. Δ(7)-STEROL-C5(6)-DESATURASE (C5-SD) in the hitherto unresolved cholesterol pathway is a direct target of GAME9. Transactivation and promoter-binding assays show that GAME9 exerts its activity either directly or cooperatively with the SlMYC2 transcription factor as in the case of the C5-SD gene promoter. Our findings provide insight into the regulation of SGA biosynthesis and means for manipulating these metabolites in crops.
Highlights
Steroidal glycoalkaloids (SGAs) are cholesterol-derived molecules produced by solanaceous species
We identified GLYCOALKALOID METABOLISM 9 (GAME9), an APETALA2/ Ethylene Response Factors (AP2/ERF) transcription factor that regulates the biosynthesis of steroidal alkaloids in Solanaceae plants
To examine the possible association of this regulator in the control of SGA biosynthesis, we carried out combined coexpression analysis using potato and tomato transcriptome data
Summary
Steroidal glycoalkaloids (SGAs) are cholesterol-derived molecules produced by solanaceous species. GAME9 knockdown and overexpression in tomato and potato alters expression of SGAs and upstream mevalonate pathway genes including the cholesterol biosynthesis gene STEROL SIDE CHAIN REDUCTASE 2 (SSR2). Steroidal alkaloids (SAs) and their glycosylated forms (steroidal glycoalkaloids; SGAs) are nitrogen-containing toxic compounds occurring primarily in the Solanaceae and Liliaceae plant families[1]. This class of metabolites is produced in Solanaceae vegetable crops such as potato, tomato and eggplant. Itkin et al.[5] reported a set of GLYCOALKALOID METABOLISM (GAME) genes that participate in the core pathway producing SGAs in both potato and tomato. Overexpression of a soybean SMT1 in potato plants increased the metabolic flux of cycloartenol into alkylated sterols at the expense of cholesterol[21]
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