Independent and interdependent functions of LAF1 and HFR1 in phytochrome A signaling
Independent and interdependent functions of LAF1 and HFR1 in phytochrome A signaling
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DOI：
10.1101/gad.1568207
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发表时间：
2007-08-15
影响因子：
10.5
通讯作者：
Chua, Nam-Hai
中科院分区：
文献类型：
--
作者：
Jang, In-Cheol;Yang, Seong Wook;Chua, Nam-Hai
光敏色素 A 信号传导-e 的几种正调节因子。例如，LAF1、HFR1 和 HY5 在光感受器下游起作用，但它们在转导途径中的相对作用位点尚不清楚。在这里，我们表明，与单突变体 hfr1-201 或 laf1 相比，通过 RNA 干扰 (RNAi) 产生的 HFR1RNAi/laf1 或 hfr1-201/LAF1RNAi 在 FR 光下具有加性表型。该结果表明 LAF1 和 HFR1 在很大程度上独立的途径中发挥作用。 LAF1（一种 R2R3-MYB 因子）与 HFR1（一种碱性螺旋-环-螺旋 (bHLH) 因子）相互作用，并且这种相互作用因 LAF1 R2R3 结构域中的 R97A 突变而消除。体外 COP1 E3 连接酶对 LAF1 和 HFR1 的多泛素化会受到 LAF1/HFR1 关联的抑制。与该结果一致，与野生型相比，内源HFR1在laf1中的稳定性较差，并且类似地，从转基因表达的LAF1-3HA在hfr1-201中也比野生型不稳定。在转基因植物中，HFR1 水平在 LAF1 而非 LAF1(R97A) 的诱导表达后显着升高。此外，LAF1（而非 LAF1（R97A））的诱导表达延迟了 FR 光下 HFR1 的翻译后降解。 HFR1 和 LAF1 的组成型共表达（而非 HFR1 和 LAF1 (R97A)）在双转基因植物中赋予 FR 超敏性。我们的结果表明，除了在 phyA 信号传导中发挥独立功能外，LAF1 和 HFR1 还在翻译后合作，通过 COP1 抑制泛素化来稳定彼此，从而增强 phyA 光响应。
Several positive regulators of phytochrome A signaling-e. g., LAF1, HFR1, and HY5-operate downstream from the photoreceptor, but their relative sites of action in the transduction pathway are unknown. Here, we show that HFR1RNAi/laf1 or hfr1-201/LAF1RNAi generated by RNA interference (RNAi) has an additive phenotype under FR light compared with the single mutants, hfr1-201 or laf1. This result indicates that LAF1 and HFR1 function in largely independent pathways. LAF1, an R2R3-MYB factor, interacts with HFR1, a basic helix-loop-helix ( bHLH) factor, and this interaction is abolished by the R97A mutation in the LAF1 R2R3 domain. Polyubiquitinations of LAF1 and HFR1 by the COP1 E3 ligase in vitro are inhibited by LAF1/HFR1 association. Consistent with this result, endogenous HFR1 is less stable in laf1 compared with wild type, and similarly, LAF1-3HA expressed from a transgene is also less stable in hfr1-201 than wild type. In transgenic plants, HFR1 levels are significantly elevated upon induced expression of LAF1 but not LAF1( R97A). Moreover, induced expression of LAF1 but not LAF1( R97A) delays post-translational HFR1 degradation in FR light. Constitutive coexpression of HFR1 and LAF1 but not HFR1 and LAF1 ( R97A) confers FR hypersensitivity in double transgenic plants. Our results show that in addition to their independent functions in phyA signaling, LAF1 and HFR1 also cooperate post-translationally to stabilize each other through inhibition of ubiquitination by COP1, thereby enhancing phyA photoresponses.