UNRAVELING THE REGULATION OF NITROGEN ASSIMILATION IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE): DIURNAL VARIATIONS IN TRANSCRIPT LEVELS FOR FIVE GENES INVOLVED IN NITROGEN ASSIMILATION
UNRAVELING THE REGULATION OF NITROGEN ASSIMILATION IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE): DIURNAL VARIATIONS IN TRANSCRIPT LEVELS FOR FIVE GENES INVOLVED IN NITROGEN ASSIMILATION
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DOI：
10.1111/j.1529-8817.2009.00648.x
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发表时间：
2009-04-01
影响因子：
2.9
通讯作者：
Robertson, Deborah L.
中科院分区：
文献类型：
--
作者：
Brown, Kathryn L.;Twing, Katrina I.;Robertson, Deborah L.
我们研究了海洋硅藻Thalassiosira pponana(Hust.)中五个氮同化酶基因的日表达。Hasle et Heimdal在从NH4+-到NO3--添加的培养基上转换后。NIA转录本(编码硝酸还原酶，NR)在过渡到添加硝酸盐的培养基后的积累与先前报道的NR丰度和活性的变化相似。NIA基因的表达水平呈昼夜变化，当细胞转入连续光照时，这种昼夜振荡现象被消除。在假单胞藻基因组中发现了编码叶绿体(NiA)和胞质(Nirb)亚硝酸还原酶的基因。NIIA和Nirb的转录水平在加入NO3-后2小时内升高，并呈昼夜变化。NIA、NIIA和glnII(编码叶绿体定位的谷氨酰胺合成酶)mRNA丰度的日变化模式相似。Nirb和glnN(编码胞浆定位的谷氨酰胺合成酶)的mRNA水平也有昼夜振荡；然而，这种振荡与NIA、NiIA和glnII是异相的。我们认为NO3-在硅藻的叶绿体和胞浆中都被同化为有机分子，Nirb和glnN编码的酶对海洋硅藻中观察到的NO3-的暗同化具有重要的生态意义。与NIA一样，当细胞转移到连续光照下时，NiIA、Nirb、glnII和glnN的日变化被消除。我们的结果表明，转录积累不是昼夜节律控制的，而是由明：暗(L：D)转换引发的代谢池的变化可能在调节编码这些关键的氮同化酶的细胞基因水平方面起重要作用。
We examined the diurnal expression of five genes encoding nitrogen-assimilating enzymes in the marine diatom Thalassiosira pseudonana (Hust.) Hasle et Heimdal following a transition from NH4+- to NO3--supplemented media. The accumulation of nia transcripts (encoding nitrate reductase, NR) following the transition to NO3--supplemented media was similar to previously reported changes in NR abundance and activity. Nia mRNA levels varied diurnally, and the diurnal oscillations were abolished when cells were transferred to continuous light. Genes encoding chloroplastic (niiA) and cytosolic (nirB) nitrite reductases were identified in the genome of T. pseudonana. NiiA and nirB transcript levels increased within 2 h following the addition of NO3- and varied diurnally. Patterns of diurnal variation in nia, niiA, and glnII (encoding the chloroplast-localized glutamine synthetase) mRNA abundances were similar. NirB and glnN (encoding the cytosolic-localized glutamine synthetase) mRNA levels also oscillated diurnally; however, the oscillation was out of phase with nia, niiA, and glnII. We propose that NO3- is assimilated into organic molecules in both the chloroplast and cytosol of diatoms and that enzymes encoded by nirB and glnN contribute to the ecologically important dark assimilation of NO3- observed in marine diatoms. As with nia, the diurnal variations in niiA, nirB, glnII, and glnN were abolished when cells were transferred to continuous light. Our results demonstrate that transcript accumulation is not circadian controlled, but, rather, changes in metabolic pools triggered by light:dark (L:D) transitions may be important in regulating the cellular mRNA levels encoding these key nitrogen assimilating enzymes.