Wang Hai, Lu Yuqing, Liu Pei, Wen Wei, Zhang Jianhua, Ge Xiaochun, Xia Yiji
Department of Biology, Hong Kong Baptist University, Hong Kong, China.
State Key Laboratory of Genetic Engineering, Institute of Plant Biology, Department of Biochemistry and Molecular Biology, School of Life Sciences, Fudan University, Shanghai, China.
Plant J. 2013 Jan;73(2):262-75. doi: 10.1111/tpj.12032. Epub 2012 Nov 8.
AtNUDT7 was reported to be a negative regulator of EDS1-mediated immunity in Arabidopsis. However, the underlying molecular and genetic mechanism of the AtNUDT7-regulated defense pathway remains elusive. Here we report that AtNUDT7 and its closest paralog AtNUDT6 function as novel negative regulators of SNC1, a TIR-NB-LRR-type R gene. SNC1 is upregulated at transcriptional and possibly post-transcriptional levels in nudt6-2 nudt7. The nudt6-2 nudt7 double mutant exhibits autoimmune phenotypes that are modulated by temperature and fully dependent on EDS1. The nudt6-2 nudt7 mutation causes EDS1 nuclear accumulation shortly after the establishment of autoimmunity caused by the temperature shift. We found that a low ammonium/nitrate ratio in growth media leads to a higher level of nitrite-dependent nitric oxide (NO) production in nudt6-2 nudt7, and NO acts in a positive feedback loop with EDS1 to promote the autoimmunity. The low ammonium/nitrate ratio also enhances autoimmunity in snc1-1 and cpr1, two other autoimmune mutants in Arabidopsis. Our study indicates that Arabidopsis senses the ammonium/nitrate ratio as an input signal to determine the amplitude of the EDS1-mediated defense response, probably through the modulation of NO production.
据报道，AtNUDT7是拟南芥中EDS1介导的免疫反应的负调控因子。然而，AtNUDT7调控的防御途径的潜在分子和遗传机制仍不清楚。在此我们报道，AtNUDT7及其最接近的旁系同源基因AtNUDT6作为TIR-NB-LRR型R基因SNC1的新型负调控因子发挥作用。在nudt6-2 nudt7中，SNC1在转录水平以及可能在转录后水平上被上调。nudt6-2 nudt7双突变体表现出受温度调节且完全依赖EDS1的自身免疫表型。nudt6-2 nudt7突变在温度变化引起的自身免疫建立后不久导致EDS1在细胞核中积累。我们发现，生长培养基中低铵/硝酸盐比例会导致nudt6-2 nudt7中依赖亚硝酸盐的一氧化氮（NO）产生水平升高，并且NO与EDS1以正反馈回路起作用以促进自身免疫。低铵/硝酸盐比例也增强了拟南芥中另外两个自身免疫突变体snc1-1和cpr1的自身免疫。我们的研究表明，拟南芥可能通过调节NO的产生将铵/硝酸盐比例作为输入信号来确定EDS1介导的防御反应的幅度。
