Functional analysis of an Arabidopsis T-DNA "Knockout" of the high-affinity NH4+ transporter AtAMT1;1
Functional analysis of an Arabidopsis T-DNA "Knockout" of the high-affinity NH4+ transporter AtAMT1;1
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DOI：
10.1104/pp.102.010843
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发表时间：
2002-11-01
期刊：
影响因子：
7.4
通讯作者：
Glass, ADM
中科院分区：
文献类型：
--
作者：
Kaiser, BN;Rawat, SR;Glass, ADM
植物根对NH 4+的吸收被认为涉及在植物、酵母、细菌和哺乳动物中发现的NH 4+转运蛋白家族（AMT）的成员。在拟南芥中，有六个AMT基因，其中AtAMT 1;1表现出对NH 4+的最高亲和力。氮素营养水平变化时，根中铵离子的流入量与AtAMT 1;1 mRNA的表达水平高度相关。为了进一步研究AtAMT 1;1在高亲和力NH 4+内流中的作用，我们鉴定了一个AtAMT 1;1活性被破坏的纯合T-DNA突变体。与预期相反，当在足够的N下生长时，amt 1;1：T-DNA突变体中的高亲和力（NH 4+）-N-13流入与野生型相似。与野生型植物相比，去除N以增加AtAMT 1;1表达使突变体中的高亲和力（NH 4+）-N-13流入减少了30%，而低亲和力（NH 4+）-N-13流入（250 μ M-10 mm NH 4+）超过了野生型植物。在这些N-剥夺植物，根AtAMT 1;3和AtAMT 2;1 mRNA的mRNA拷贝数显着增加的突变体比野生型植物。在大多数生长条件下，amt 1;1：T-DNA植物是从野生型难以区分的，但是，叶形态发生了变化。然而，当用NH 4+和蔗糖生长时，突变体生长不良并死亡。我们的研究结果是第一个在植物的证据表明，AtAMT 1;1是一个根NH 4+转运蛋白和AMT家族内的冗余可能会允许补偿AtAMT 1;1的损失。
NH4+ acquisition by plant roots is thought to involve members of the NH4+ transporter family (AMT) found in plants, yeast, bacteria, and mammals. In Arabidopsis, there are six AMT genes of which AtAMT1;1 demonstrates the highest affinity for NH4+. Ammonium influx into roots and AtAMT1;1 mRNA expression levels are highly correlated diurnally and when plant nitrogen (N) status is varied. To further investigate the involvement of AtAMT1;1 in high-affinity NH4+ influx, we identified a homozygous T-DNA mutant with disrupted AtAMT1;1 activity. Contrary to expectation, high-affinity (NH4+)-N-13 influx in the amt1;1:T-DNA mutant was similar to the wild type when grown with adequate N. Removal of N to increase AtAMT1;1 expression decreased high-affinity (NH4+)-N-13 influx in the mutant by 30% compared with wild-type plants, whereas low-affinity (NH4+)-N-13 influx (250 muM-10 mm NH4+) exceeded that of wild-type plants. In these N-deprived plants, mRNA copy numbers of root AtAMT1;3 and AtAMT2;1 mRNA were significantly more increased in the mutant than in wild-type plants. Under most growth conditions, amt1;1:T-DNA plants were indistinguishable from the wild type, however, leaf morphology was altered. However, when grown with NH4+ and sucrose, the mutant grew poorly and died. Our results are the first in planta evidence that AtAMT1;1 is a root NH4+ transporter and that redundancies within the AMT family may allow compensation for the loss of AtAMT1;1.