The Analysis of Arabidopsis Nicotianamine Synthase Mutants Reveals Functions for Nicotianamine in Seed Iron Loading and Iron Deficiency Responses
The Analysis of Arabidopsis Nicotianamine Synthase Mutants Reveals Functions for Nicotianamine in Seed Iron Loading and Iron Deficiency Responses
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DOI：
10.1104/pp.109.136374
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发表时间：
2009-05-01
期刊：
影响因子：
7.4
通讯作者：
Bauer, Petra
中科院分区：
文献类型：
--
作者：
Klatte, Marco;Schuler, Mara;Bauer, Petra
烟草胺在植物中螯合和运输微量营养素金属离子。据推测，烟草胺与种子中的微量营养素有关。以番茄(Solanum Lycopsicum)突变体(Loronerva)和烟草(Nictiana Tabacum)转基因株系为材料，分析了烟草胺缺失对番茄生长发育的影响。这些突变体表现为叶片提前黄化，并有不育花。拟南芥具有4个烟碱合成酶基因。我们构建了两个四重NAS突变体：一个完全丧失NAS功能，是不育的，表现为类似绿球藻的表型(nas4x-2)；另一个是中等表型的突变体(nas4x-1)，其叶片失绿，在从营养到生殖阶段过渡和铁(Fe)缺乏时变得严重。残留的烟碱水平足以维持生命周期。因此，nas4x-1突变体使我们能够研究烟碱的晚期功能。该突变体在生殖生长期的丛生叶中没有检测到烟碱，而在营养生长期的丛生叶和种子中检测到低水平的烟碱。铁在莲座叶中积累，而在花和种子中则较少。分子生理分析表明，叶片、根和花表现出缺铁的症状，而叶片也表现出充足的铁供应迹象。突变株不能充分调动铁来维持花和种子的正常供铁。因此，烟草胺是种子正确供应铁所必需的。这些结果是通过改变NAS基因来改变铁的动态平衡调节的植物操纵方法的基础。
Nicotianamine chelates and transports micronutrient metal ions in plants. It has been speculated that nicotianamine is involved in seed loading with micronutrients. A tomato (Solanum lycopersicum) mutant (chloronerva) and a tobacco (Nicotiana tabacum) transgenic line have been utilized to analyze the effects of nicotianamine loss. These mutants showed early leaf chlorosis and had sterile flowers. Arabidopsis (Arabidopsis thaliana) has four NICOTIANAMINE SYNTHASE (NAS) genes. We constructed two quadruple nas mutants: one had full loss of NAS function, was sterile, and showed a chloronerva-like phenotype (nas4x-2); another mutant, with intermediate phenotype (nas4x-1), developed chlorotic leaves, which became severe upon transition from the vegetative to the reproductive phase and upon iron (Fe) deficiency. Residual nicotianamine levels were sufficient to sustain the life cycle. Therefore, the nas4x-1 mutant enabled us to study late nicotianamine functions. This mutant had no detectable nicotianamine in rosette leaves of the reproductive stage but low nicotianamine levels in vegetative rosette leaves and seeds. Fe accumulated in the rosette leaves, while less Fe was present in flowers and seeds. Leaves, roots, and flowers showed symptoms of Fe deficiency, whereas leaves also showed signs of sufficient Fe supply, as revealed by molecular-physiological analysis. The mutant was not able to fully mobilize Fe to sustain Fe supply of flowers and seeds in the normal way. Thus, nicotianamine is needed for correct supply of seeds with Fe. These results are fundamental for plant manipulation approaches to modify Fe homeostasis regulation through alterations of NAS genes.