Table2.DOC

Steroidal glycoalkaloids (SGAs) are cholesterol-derived specialized metabolites produced by Solanaceous plant species. They contribute to pathogen defense but are considered as anti-nutritional compounds and toxic to humans. Although the genes involved in the SGA biosynthetic pathway have been successfully cloned and identified, transcription factors regulating this pathway are still poorly understood. We report that silencing tomato light signal transduction transcription factors ELONGATED HYPOCOTYL 5 (SlHY5) and PHYTOCHROME INTERACTING FACTOR3 (SlPIF3), by virus-induced gene silencing (VIGS), altered glycoalkaloids levels in tomato leaves compared to control plant. Electrophoretic mobility shift assay (EMSA) and Chromatin immunoprecipitation (ChIP) analysis confirmed that SlHY5 and SlPIF3 bind to the promoter of target genes of GLYCOALKALOID METABOLISM (GAME1, GAME4, GAME17), affecting the steady-state concentrations of transcripts coding for SGA pathway enzymes. The results indicate that light-signaling transcription factors HY5 and PIF3 regulate the abundance of SGAs by modulating the transcript levels of these GAME genes. This insight into the regulation of SGA biosynthesis can be used for manipulating the level of these metabolites in crops.

甾体糖苷生物碱（Steroidal glycoalkaloids, SGAs）是由茄科植物产生的、源自胆固醇的特化代谢物。它们在植物抵御病原体的过程中发挥作用，但同时被归类为抗营养化合物，对人体具有毒性。尽管SGA生物合成通路相关的基因已成功克隆并鉴定，但调控该通路的转录因子仍知之甚少。本研究通过病毒诱导基因沉默（virus-induced gene silencing, VIGS）技术沉默番茄光信号转导通路中的转录因子下胚轴伸长5（ELONGATED HYPOCOTYL 5, SlHY5）与光敏色素互作因子3（PHYTOCHROME INTERACTING FACTOR3, SlPIF3），结果显示，与对照植株相比，处理后的番茄叶片中糖苷生物碱含量发生了显著改变。电泳迁移率变动分析（Electrophoretic mobility shift assay, EMSA）与染色质免疫沉淀（Chromatin immunoprecipitation, ChIP）实验证实，SlHY5和SlPIF3可结合至糖苷生物碱代谢（GLYCOALKALOID METABOLISM, GAME1、GAME4、GAME17）靶基因的启动子区域，进而影响编码SGA通路酶的转录本的稳态浓度。研究结果表明，光信号通路转录因子HY5与PIF3可通过调控上述GAME基因的转录水平，调节SGA的积累量。这一关于SGA生物合成调控的研究见解，可用于定向改良作物中这类代谢物的含量水平。