TSAR1 and TSAR2 activate triterpene saponin production in Medicago truncatula. TSAR1 and TSAR2 activate triterpene saponin production in Medicago truncatula

We identified two novel transcription factors ‘Triterpene Saponin Activation Regulator’ (TSAR) 1 and 2 that each activate a specific branch of saponin synthesis in M. truncatula. Therefore we generated three independent TSAR1 and three independent TSAR2 overexpression (OE) hairy root lines. As a control we raised three independent hairy root lines expressing a non-functional GUS gene. By qRT-PCR analyses and metabolite profiling of these lines, we found that TSAR1 OE leads to accumulation of non-haemolytic saponins whereas TSAR2 instigates accumulation of haemolytic saponins. To identify additional targets of TSAR1 and TSAR2 we carried out a genome-wide transcript profiling study by RNA-Seq.

本研究鉴定得到两个新型转录因子——三萜皂苷激活调节因子（Triterpene Saponin Activation Regulator，TSAR）1与2，二者可分别激活蒺藜苜蓿（M. truncatula）中皂苷生物合成的特定分支。据此，我们构建了3个独立的TSAR1过表达（OE）发根株系，以及3个独立的TSAR2过表达发根株系，并以表达无功能β-葡萄糖苷酸酶（GUS）基因的3个独立发根株系作为对照。通过对上述株系开展实时定量逆转录PCR（qRT-PCR）分析与代谢物谱分析，我们发现TSAR1过表达可诱导非溶血性皂苷积累，而TSAR2过表达则会促进溶血性皂苷积累。为鉴定TSAR1与TSAR2的其他潜在靶标，我们通过RNA测序（RNA-Seq）完成了全基因组转录谱分析研究。