Abstract
Duckweed plants play important roles in aquatic ecosystems worldwide. They rapidly accumulate biomass and have potential uses in bioremediation of water polluted by fertilizer runoff or other chemicals. Here we studied the assimilation of two major sources of inorganic nitrogen, nitrate () and ammonium (), in six duckweed species: Spirodela polyrhiza, Landoltia punctata, Lemna aequinoctialis, Lemna turionifera, Lemna minor, and Wolffia globosa. All six duckweed species preferred over and started using only when was depleted. Using the available genome sequence, we analyzed the molecular structure and expression of eight key nitrogen assimilation genes in S. polyrhiza. The expression of genes encoding nitrate reductase and nitrite reductase increased about 10-fold when was supplied and decreased when was supplied. and induced the glutamine synthetase (GS) genes GS1;2 and the GS2 by 2- to 5-fold, respectively, but repressed GS1;1 and GS1;3. and upregulated the genes encoding ferredoxin- and NADH-dependent glutamate synthases (Fd-GOGAT and NADH-GOGAT). A survey of nitrogen assimilation gene promoters suggested complex regulation, with major roles for NRE-like and GAATC/GATTC cis-elements, TATA-based enhancers, repeats, and G-quadruplex structures. These results will inform efforts to improve bioremediation and nitrogen use efficiency.
Highlights
The application of nitrogen (N) fertilizers produced substantial crop yield increases, but N fertilizers cause serious environmental problems [1]
Identity of the Analy2z. eRdesSupltescies The duckweeds u2s.1e. dIdeinntitythofisthesAtunadlyyzedinScpleuciedse five species isolated in Eastern China (Spirodela polyrhiza, LandoltiTahpe udnucktawteae,dLseumsneda ianeqthuisinsotucdtiyaliinsc,luLd. etufirvieonspifeecriaes, aisnodlatWedoilnffiEaasgtleorbnoCsha)ina and Lemna minor, colle(Scpteirdodeilna pKolayzrhaizkah, sLtaanndo.ltiPa rpiuonrcttaota,thLeemNna aaseqsuiimnoicltaiatliiso, nL.etxuprieonriifmerae, nantsd, tWhoelffia identity of all species eggxlorpboeorswiam)neanintnsd, tvhLietemridoneanftrimotyimnoofr,aallcssoiplnleegccitleeesdgfrrionownnKdainzwavkiahtrssotacfnroo. mnPfiarirosmirngetlode ftrbhoyendbNwaarascscosoidmnifiinlramgtioedn through sequencing thbeyabtaprFco–daitnpgHth(rAouTgPh)saeqnudenpcsinbgKt–hpesabtLpF(–PatSpHB)(AinTtPe)ragnednpiscbKs–ppasbcLer(PsS[B3)8in]taerngdenic using BLAST searchessapgacaeirns s[3t8t]haendNuCsiBngI BsLeAquSTensecaercchoesllaegcatiinostnth[e39N]C
To estimate duckweed growth responses to NO3− and NH4+, all six duckweed species were cultivated under identical temperature and light conditions in 200 mL of liquid SH
Summary
The application of nitrogen (N) fertilizers produced substantial crop yield increases, but N fertilizers cause serious environmental problems [1]. Water eutrophication is a global concern, and a major environmental problem for water resource management. This is especially true in China, which has increased food crop production remarkably during recent decades, largely due to the extensive application of N fertilizers. The resulting runoff has led to some regions substantially exceeding the surface-water quality standard of 1 mg N/L. Remedying these problems requires transformative changes to boost N recycling; implementing these changes was recently estimated to cost China $18–29 billion per year [4]
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