Division of Plant and Crop Sciences, School of Biosciences and Centre for Plant Integrative Biology, University of Nottingham, Loughborough LE12 5RD, UK.
Nature. 2011 Oct 23;479(7373):415-8. doi: 10.1038/nature10534.
Plants and animals are obligate aerobes, requiring oxygen for mitochondrial respiration and energy production. In plants, an unanticipated decline in oxygen availability (hypoxia), as caused by roots becoming waterlogged or foliage submergence, triggers changes in gene transcription and messenger RNA translation that promote anaerobic metabolism and thus sustain substrate-level ATP production. In contrast to animals, oxygen sensing has not been ascribed to a mechanism of gene regulation in response to oxygen deprivation in plants. Here we show that the N-end rule pathway of targeted proteolysis acts as a homeostatic sensor of severe low oxygen levels in Arabidopsis, through its regulation of key hypoxia-response transcription factors. We found that plants lacking components of the N-end rule pathway constitutively express core hypoxia-response genes and are more tolerant of hypoxic stress. We identify the hypoxia-associated ethylene response factor group VII transcription factors of Arabidopsis as substrates of this pathway. Regulation of these proteins by the N-end rule pathway occurs through a characteristic conserved motif at the amino terminus initiating with Met-Cys. Enhanced stability of one of these proteins, HRE2, under low oxygen conditions improves hypoxia survival and reveals a molecular mechanism for oxygen sensing in plants via the evolutionarily conserved N-end rule pathway. SUB1A-1, a major determinant of submergence tolerance in rice, was shown not to be a substrate for the N-end rule pathway despite containing the N-terminal motif, indicating that it is uncoupled from N-end rule pathway regulation, and that enhanced stability may relate to the superior tolerance of Sub1 rice varieties to multiple abiotic stresses.
动植物都是需氧生物，需要氧气进行线粒体呼吸和能量产生。在植物中，由于根系积水或叶片淹没等原因导致氧气供应意外下降（缺氧），会引发基因转录和信使 RNA 翻译的变化，促进无氧代谢，从而维持底物水平的 ATP 产生。与动物不同，氧气感应尚未被归因于植物缺氧时响应氧气剥夺的基因调控机制。在这里，我们表明，靶向蛋白酶解的 N 端规则途径通过调节关键的低氧应答转录因子，作为拟南芥严重低氧水平的体内平衡传感器。我们发现，缺乏 N 端规则途径组分的植物持续表达核心低氧应答基因，并且对低氧胁迫更耐受。我们确定拟南芥与低氧相关的乙烯应答因子 VII 转录因子是该途径的底物。该途径通过起始于 Met-Cys 的特征保守基序调节这些蛋白。在低氧条件下，这些蛋白之一 HRE2 的稳定性增强提高了低氧存活率，并通过进化上保守的 N 端规则途径揭示了植物氧气感应的分子机制。尽管水稻耐淹没的主要决定因素 SUB1A-1 含有 N 端基序，但它不是 N 端规则途径的底物，这表明它与 N 端规则途径的调节无关，并且稳定性的增强可能与 Sub1 水稻品种对多种非生物胁迫的更高耐受性有关。
