The basic helix-loop-helix transcription factor CrMYC2 controls the jasmonate-responsive expression of the ORCA genes that regulate alkaloid biosynthesis in Catharanthus roseus
The basic helix-loop-helix transcription factor CrMYC2 controls the jasmonate-responsive expression of the ORCA genes that regulate alkaloid biosynthesis in Catharanthus roseus
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DOI：
10.1111/j.1365-313x.2011.04575.x
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发表时间：
2011-07-01
期刊：
影响因子：
7.2
通讯作者：
Memelink, Johan
中科院分区：
文献类型：
--
作者：
Zhang, Hongtao;Hedhili, Sabah;Memelink, Johan
茉莉酸是植物信号分子，在防御昆虫和某些病原体方面发挥关键作用，其中包括通过控制保护性次级代谢产物的生物合成。在长春花中，AP 2/ERF结构域转录因子ORCA 3控制着几个编码萜类吲哚生物碱生物合成酶的基因的茉莉酸响应性表达。ORCA 3基因表达本身由茉莉酸诱导。ORCA 3启动子包含一个自主茉莉酸响应元件（JRE），由负责高水平表达的定量序列和响应甲基茉莉酸（MeJA）的定性序列组成。在这里，我们确定了基本的螺旋-环-螺旋（bHLH）转录因子CrMYC 2作为MeJA响应ORCA 3基因表达的主要激活因子。CrMYC 2基因是一个即时早期茉莉酸响应基因。CrMYC 2在体外与ORCA 3 JRE中的定性序列结合，并在瞬时测定中通过该序列反式激活报告基因表达。通过RNA干扰敲低CrMYC 2表达水平导致MeJA响应性ORCA 3 mRNA积累水平大幅降低。此外，相关转录因子基因ORCA 2的MeJA响应性表达显著降低。我们的研究结果表明，MeJA反应表达的生物碱生物合成基因在C。roseus由调节ORCA基因表达的bHLH蛋白CrMYC 2和AP 2/ERF结构域转录因子ORCA 2和ORCA 3组成的转录因子级联控制，所述转录因子ORCA 2和ORCA 3又调节生物碱生物合成基因的子集。
Jasmonates are plant signalling molecules that play key roles in defence against insects and certain pathogens, among others by controlling the biosynthesis of protective secondary metabolites. In Catharanthus roseus, the AP2/ERF-domain transcription factor ORCA3 controls the jasmonate-responsive expression of several genes encoding enzymes involved in terpenoid indole alkaloid biosynthesis. ORCA3 gene expression is itself induced by jasmonate. The ORCA3 promoter contains an autonomous jasmonate-responsive element (JRE) composed of a quantitative sequence responsible for the high level of expression and a qualitative sequence that acts as an on/off switch in response to methyl-jasmonate (MeJA). Here, we identify the basic helix-loop-helix (bHLH) transcription factor CrMYC2 as the major activator of MeJA-responsive ORCA3 gene expression. The CrMYC2 gene is an immediate-early jasmonate-responsive gene. CrMYC2 binds to the qualitative sequence in the ORCA3 JRE in vitro, and transactivates reporter gene expression via this sequence in transient assays. Knock-down of the CrMYC2 expression level via RNA interference caused a strong reduction in the level of MeJA-responsive ORCA3 mRNA accumulation. In addition, MeJA-responsive expression of the related transcription factor gene ORCA2 was significantly reduced. Our results show that MeJA-responsive expression of alkaloid biosynthesis genes in C. roseus is controlled by a transcription factor cascade consisting of the bHLH protein CrMYC2 regulating ORCA gene expression, and the AP2/ERF-domain transcription factors ORCA2 and ORCA3, which in turn regulate a subset of alkaloid biosynthesis genes.