MYB31转录因子的天然变异导致极辣辣椒的形成

Natural Variations in the MYB Transcription Factor MYB31 Determine the Evolution of Extremely Pungent Peppers

植物产生大量代谢产物参与发育和环境适应,这当中许多代谢产物具有重要的生物活性。辣椒素及其类似物统称辣椒素类物质,是辣椒属植物特有的一类次生代谢产物,赋予辣椒果实辣味,并且具有广泛的应用价值。在辣椒5个栽培驯化种中,Capsicum chinense果实辣椒素类物质含量极高,导致该栽培种极其辛辣。然而辣椒素合成相关基因特异在辣椒中获得转录,导致极辣辣椒形成的机制尚不清楚。本研究采用遗传学和基因功能验证手段,找到一个数量性状位座点Capsaicinoid1 (Cap1,又名Pun3)。进一步研究发现,Cap1/Pun3位点编码一个茄科植物特有的MYB转录因子MYB31。MYB31在辣椒属胎座中特异表达,并激活辣椒素合成途径相关基因使得辣椒素类物质在辣椒果实中合成。MYB31的转录水平决定辣椒素类物质含量。MYB31启动子在不同种辣椒存在差异,在C.chinense种中由于启动子存在一个W-box使得其可以被一个胎座特异转录的WRKY9转录因子识别并激活导致MYB31获得高水平转录并强烈激活辣椒素合成相关基因,最终导致辣椒素类物质大量合成。

Plants produce countless specialized metabolites crucial for their development and fitness,and many are useful bioactive compounds.Capsaicinoids are intriguing genus-specialized metabolites that confer a pungent flavor to Capsicum fruits,and they are widely applied in different areas.Among the five domesticated Capsicum species,Capsicum chinense has a high content of capsaicinoids,which results in an extremely hot flavor.However,the speciesspecific upregulation of capsaicinoid-biosynthetic genes (CBGs) and the evolution of extremely pungent peppers are not well understood.We conducted genetic and functional analyses demonstrating that the quantitative trait locus Capsaicinoid1 (Cap1),which is identical to Pun3 contributes to the level of pungency.The Cap1/Pun3 locus encodes the Solanaceae-specific MYB transcription factor MYB31.Capsicum species have evolved placenta-specific expression of MYB31,which directly activates expression of CBGs and results in genus-specialized metabolite production.The capsaicinoid content depends on MYB31 expression.Natural variations in the MYB31 promoter increase MYB31 expression in C.chinense via the binding of the placenta-specific expression of transcriptional activator WRKY9 and augmentation of CBG expression,which promotes capsaicinoid biosynthesis.Our findings provide insights into the evolution of extremely pungent C.chinense,which is due to natural variations in the master regulator,and offers targets for engineering or selecting flavor in Capsicum.