Key Laboratory of Applied Marine Biotechnology, Ningbo University, Ningbo, Zhejiang, China.
PLoS One. 2018 Mar 7;13(3):e0193458. doi: 10.1371/journal.pone.0193458. eCollection 2018.
The Mediator complex is at the core of transcriptional regulation and plays a central role in plant immunity. The MEDIATOR25 (MED25) subunit of Arabidopsis thaliana regulates jasmonate-dependent resistance to Botrytis cinerea through interacting with the basic helix-loop-helix (bHLH) transcription factor of jasmonate signaling, MYC2. Another Mediator subunit, MED8, acts independently or together with MED25 in plant immunity. However, unlike MED25, the underlying action mechanisms of MED8 in regulating B. cinerea resistance are still unknown. Here, we demonstrated that MED8 regulated plant immunity to B. cinerea through interacting with another bHLH transcription factor, FAMA, which was previously shown to control the final proliferation/differentiation switch during stomatal development. Our research demonstrates that FAMA is also an essential component of B. cinerea resistance. The fama loss-of-function mutants (fama-1 and fama-2) increased susceptibility to B. cinerea infection and reduced defense-gene expression. On the contrary, transgenic lines constitutively overexpressing FAMA showed opposite B. cinerea responses compared with the fama loss-of-function mutants. FAMA-overexpressed plants displayed enhanced resistance to B. cinerea infection and increased expression levels of defensin genes following B. cinerea treatment. Genetic analysis of MED8 and FAMA suggested that FAMA-regulated pathogen resistance was dependent on MED8. In addition, MED8 and FAMA were both associated with the G-box region in the promoter of ORA59. Our findings indicate that the MED8 subunit of the A. thaliana Mediator regulates plant immunity to B. cinerea through interacting with the transcription factor FAMA, which was discovered to be a key component in B. cinerea resistance.
中介复合物是转录调控的核心，在植物免疫中发挥着核心作用。拟南芥的中介复合物 25（MED25）亚基通过与茉莉酸信号的基本螺旋-环-螺旋（bHLH）转录因子 MYC2 相互作用，调节茉莉酸依赖的对灰葡萄孢的抗性。另一个中介复合物亚基 MED8 在植物免疫中独立或与 MED25 一起发挥作用。然而，与 MED25 不同，MED8 调节对灰葡萄孢抗性的潜在作用机制尚不清楚。在这里，我们证明 MED8 通过与另一个 bHLH 转录因子 FAMA 相互作用来调节植物对灰葡萄孢的免疫，而 FAMA 先前被证明控制了气孔发育过程中的最终增殖/分化开关。我们的研究表明，FAMA 也是灰葡萄孢抗性的一个重要组成部分。fama 功能丧失突变体（fama-1 和 fama-2）增加了对灰葡萄孢感染的敏感性，并降低了防御基因的表达。相反，组成型过表达 FAMA 的转基因系与 fama 功能丧失突变体相比表现出相反的灰葡萄孢反应。与 fama 功能丧失突变体相比，FAMA 过表达植物在灰葡萄孢感染后表现出增强的抗性和防御基因表达水平的增加。MED8 和 FAMA 的遗传分析表明，FAMA 调节的病原体抗性依赖于 MED8。此外，MED8 和 FAMA 都与 ORA59 启动子中的 G-框区域相关。我们的研究结果表明，拟南芥中介复合物的 MED8 亚基通过与转录因子 FAMA 相互作用来调节植物对灰葡萄孢的免疫，而 FAMA 被发现是灰葡萄孢抗性的关键组成部分。
