Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
Mol Biol Rep. 2011 Oct;38(7):4797-804. doi: 10.1007/s11033-010-0621-1. Epub 2010 Dec 14.
Ammonium (NH(4) (+)) transport is a key process in nitrogen metabolism. To elucidate the role of ammonium transporters in the nitrogen consumption of the salt-resistant green alga, Dunaliella viridis, two ammonium transporter genes, DvAMT1;1 and DvAMT1;2, were isolated from cDNA libraries of D. viridis. DvAMT1;1 and DvAMT1;2 share only 40% amino acid identity, indicating that they have highly divergent coding sequences. Functional complementation in a yeast mutant defective in ammonium uptake indicated that both DvAMT1;1 and DvAMT1;2 were functional ammonium transporters. Quantitative RT-PCR showed similar expression patterns, but different transcript abundance levels, for DvAMT1;1 and DvAMT1;2 under different nitrogen conditions. Both were induced at low nitrogen and inhibited at high nitrogen concentrations, especially when NH(4) (+) was the nitrogen source. At the transcriptional level, DvAMT1;1 was diurnally regulated, while DvAMT1;2 was not. In addition, under NaCl concentrations that ranged from 0.5 to 3 M, DvAMT1;1 was down-regulated at the higher salt conditions; conversely, DvAMT1;2 maintained a relatively low, but stable, transcript abundance. The observed differences in transcriptional regulation of DvAMT1;1 and DvAMT1;2 are indicative of their diverse physiological functions in D. viridis.
铵（NH(4) (+)）转运是氮代谢中的关键过程。为了阐明铵转运体在耐盐绿藻杜氏盐藻氮消耗中的作用，从杜氏盐藻 cDNA 文库中分离出两个铵转运体基因 DvAMT1;1 和 DvAMT1;2。DvAMT1;1 和 DvAMT1;2 仅共享 40%的氨基酸同一性，表明它们具有高度分化的编码序列。在酵母突变体中功能互补，该突变体在铵摄取中缺陷，表明 DvAMT1;1 和 DvAMT1;2 都是功能性铵转运体。定量 RT-PCR 显示，在不同氮条件下，DvAMT1;1 和 DvAMT1;2 的表达模式相似，但转录物丰度水平不同。在低氮和高氮浓度下（特别是当 NH(4) (+) 为氮源时），两者均被诱导。在转录水平上，DvAMT1;1 呈昼夜节律调节，而 DvAMT1;2 则不受昼夜节律调节。此外，在 0.5 至 3 M 的 NaCl 浓度范围内，DvAMT1;1 在较高盐条件下下调；相反，DvAMT1;2 保持相对较低但稳定的转录物丰度。DvAMT1;1 和 DvAMT1;2 的转录调控观察到的差异表明它们在杜氏盐藻中具有不同的生理功能。
