Peng Mingsheng, Hannam Carol, Gu Honglan, Bi Yong-Mei, Rothstein Steven J
Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada.
Plant J. 2007 Apr;50(2):320-37. doi: 10.1111/j.1365-313X.2007.03050.x. Epub 2007 Mar 12.
Abundant nitrogen is required for the optimal growth and development of plants, while numerous biotic and abiotic factors that consume soil nitrogen frequently create a nitrogen limitation growth condition. To cope with this, plants have evolved a suite of adaptive responses to nitrogen limitation. However, the molecular mechanism governing the adaptability of plants to nitrogen limitation is totally unknown because no reported mutant defines this trait. Here we isolated an Arabidopsis mutant, nla (nitrogen limitation adaptation), and identified the NLA gene as an essential component in this molecular mechanism. Supplied with insufficient inorganic nitrogen (nitrate or ammonium), the nla mutant failed to develop the essential adaptive responses to nitrogen limitation, but senesced much earlier and more rapidly than did the wild type. Under other stress conditions including low phosphorus nutrient, drought and high temperature, the nla mutant did not show this early senescence phenotype, but closely resembled the wild type in growth and development. Map-based cloning of NLA revealed that this gene encodes a RING-type ubiquitin ligase, and nla is a deletion mutation which does not code for the RING domain in the NLA protein. The NLA protein is localized to the nuclear speckles, where this protein interacts with the Arabidopsis ubiquitin conjugase 8 (AtUBC8). In the nla mutant, the deletion of the RING domain from NLA altered its subcellular localization, disrupted the interaction between NLA and AtUBC8 and caused the early senescence phenotype induced by low inorganic nitrogen. All the results indicate that NLA is a positive regulator for the development of the adaptability of Arabidopsis to nitrogen limitation.
植物的最佳生长和发育需要充足的氮，而消耗土壤氮的众多生物和非生物因素常常造成氮限制生长条件。为应对此情况，植物进化出了一系列对氮限制的适应性反应。然而，由于没有已报道的突变体定义这一性状，控制植物对氮限制适应性的分子机制完全未知。在此，我们分离出一个拟南芥突变体nla（氮限制适应性），并鉴定出NLA基因是这一分子机制的一个关键组分。在无机氮（硝酸盐或铵）供应不足的情况下，nla突变体无法产生对氮限制的关键适应性反应，而是比野生型更早且更快地衰老。在包括低磷养分、干旱和高温在内的其他胁迫条件下，nla突变体未表现出这种早期衰老表型，而是在生长和发育方面与野生型非常相似。基于图谱的NLA克隆显示，该基因编码一种RING型泛素连接酶，且nla是一个缺失突变，不编码NLA蛋白中的RING结构域。NLA蛋白定位于核斑点，在那里该蛋白与拟南芥泛素缀合酶8（AtUBC8）相互作用。在nla突变体中，NLA的RING结构域缺失改变了其亚细胞定位，破坏了NLA与AtUBC8之间的相互作用，并导致了由低无机氮诱导的早期衰老表型。所有结果表明，NLA是拟南芥对氮限制适应性发育的一个正向调节因子。
