Department of Advanced Bioscience, Faculty of Agriculture, Kinki University, Nara 631-8505, Japan.
Plant Physiol. 2010 Apr;152(4):2000-12. doi: 10.1104/pp.110.153569. Epub 2010 Feb 24.
Here, we investigated the physiological role of Arabidopsis (Arabidopsis thaliana) AtNUDX6, the gene encoding ADP-ribose (Rib)/NADH pyrophosphohydrolase, using its overexpressor (Pro35S:AtNUDX6) or disruptant (KO-nudx6). The level of NADH in Pro35S:AtNUDX6 and KO-nudx6 plants was decreased and increased, respectively, compared with that of the control plants, while the level of ADP-Rib was not changed in either plant. The activity of pyrophosphohydrolase toward NADH was enhanced and reduced in the Pro35S:AtNUDX6 and KO-nudx6 plants, respectively. The decrease in the activity of NADH pyrophosphohydrolase and the increase in the level of NADH were observed in the rosette and cauline leaves, but not in the roots, of the KO-nudx6 plants. Notably, the expression level of AtNUDX6 and the activity of NADH pyrophosphohydrolase in the control plants, but not in the KO-nudx6 plants, were increased by the treatment with salicylic acid (SA). The expression of SA-induced genes (PR1, WRKY70, NIMIN1, and NIMIN2) depending on NONEXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1), a key component required for pathogen resistance, was significantly suppressed and enhanced in the KO-nudx6 and Pro35S:AtNUDX6 plants, respectively, under the treatment with SA. Induction of thioredoxin h5 (TRX-h5) expression, which catalyzes a SA-induced NPR1 activation, was suppressed and accelerated in the KO-nudx6 and Pro35S:AtNUDX6 plants, respectively. The expression of isochorismate synthase1, required for the regulation of SA synthesis through the NPR1-mediated feedback loop, was decreased and increased in the KO-nudx6 and Pro35S:AtNUDX6 plants, respectively. Judging from seed germination rates, the KO-nudx6 plants had enhanced sensitivity to the toxicity of high-level SA. These results indicated that AtNUDX6 is a modulator of NADH rather than ADP-Rib metabolism and that, through induction of TRX-h5 expression, AtNUDX6 significantly impacts the plant immune response as a positive regulator of NPR1-dependent SA signaling pathways.
在这里，我们利用拟南芥（Arabidopsis thaliana）AtNUDX6 基因的过表达植株（Pro35S:AtNUDX6）和敲除突变体（KO-nudx6）研究了该基因编码的 ADP-核糖（Rib）/NADH 焦磷酸水解酶的生理功能。与对照植株相比，Pro35S:AtNUDX6 植株中的 NADH 水平降低，而 KO-nudx6 植株中的 NADH 水平升高，而两种植株中的 ADP-Rib 水平均未发生改变。Pro35S:AtNUDX6 和 KO-nudx6 植株中 NADH 焦磷酸水解酶对 NADH 的活性分别增强和减弱。KO-nudx6 植株的莲座叶和茎生叶中 NADH 焦磷酸水解酶活性降低，NADH 水平升高，但根部未发生改变。值得注意的是，水杨酸（SA）处理可提高对照植株中 AtNUDX6 的表达水平和 NADH 焦磷酸水解酶的活性，但 KO-nudx6 植株中则不然。SA 诱导基因（PR1、WRKY70、NIMIN1 和 NIMIN2）的表达依赖于非发病相关基因 1（NPR1），NPR1 是植物抗病所必需的关键组成部分，在 KO-nudx6 和 Pro35S:AtNUDX6 植株中，SA 处理后其表达分别受到显著抑制和增强。硫氧还蛋白 h5（TRX-h5）的表达受到诱导，而 TRX-h5 可催化 SA 诱导的 NPR1 激活，KO-nudx6 和 Pro35S:AtNUDX6 植株中的诱导分别受到抑制和加速。异分支酸合酶 1 的表达受到调控，SA 合成通过 NPR1 介导的反馈回路，KO-nudx6 和 Pro35S:AtNUDX6 植株中的表达分别降低和升高。从种子发芽率来看，KO-nudx6 植株对高水平 SA 的毒性更为敏感。这些结果表明，AtNUDX6 是 NADH 代谢的调节剂，而不是 ADP-Rib 代谢的调节剂，通过诱导 TRX-h5 的表达，AtNUDX6 作为 NPR1 依赖性 SA 信号通路的正调节剂，显著影响植物的免疫反应。
