Project description:Plants aquire nitrogen from the soil, most commonly in the form of either nitrate or ammonium. Unlike ammonium, nitrate must be reduced (with NADH and ferredoxin as electron donors) prior to assimilation. Thus, nitrate nutrition imposes a substantially greater energetic cost than ammonium nutrition. Our goal was to compare the transcriptomes of nitrate-supplied and ammonium-supplied plants, with a particular interest in characterizing the differences in redox metabolism elicited by different forms of inorganic nitrogen. We used microarrays to compare the short-term transcriptional response to either nitrogen supply or ammonium supply in Arabidopsis roots. Genes upregulated or downregulated by nitrate only, ammonium only, or both ammonium and nitrate were identified and analyzed.
Project description:Abstract: A large part of the nitrogen in forest soils is found in recalcitrant organic matter-protein complexes. Ectomycorrhizal fungi are thought to have a key role in the decomposition and mobilization of nitrogen from such complexes. The knowledge on the functional mechanisms of these processes, and how they are regulated by carbon from the host plant and the availability of more easily available forms of nitrogen sources are limited. We used spectroscopic analyses and transcriptome profiling to examine how the presence/absence of glucose and ammonium regulates the decomposition and mobilization of nitrogen from litter material by the ectomycorrhizal fungus Paxillus involutus. Amendments of glucose triggered the assimilation of nitrogen and the decomposition of the litter material. Concomitantly, the expression of genes encoding enzymes involved in oxidative (i.e. Fenton chemistry) degradation of polysaccharides and polyphenols, peptidases, nitrogen transporters and enzymes in pathways of the nitrogen and carbon metabolism were upregulated in concert. Addition of ammonium had minute effects on both the expression of transcripts and decomposition of litter material, and only when glucose was present. Based on the spectroscopic analyses, three major types of chemical modifications of the litter material were observed. Each of them was correlated with the expression of specific sets of genes encoding extracellular enzymes. Our data suggests that the expression of the decomposition and nitrogen assimilation machinery of ectomycorrhizal fungi can be firmly regulated by the host carbon supply, i.e. priming, and that the availability of inorganic nitrogen as such has limited effects on the saprotrophic activities. Rineau F, Shah F., Smits M.M., Persson P., Johansson T., Carleer R., Troein C., Tunlid A. (2013) Carbon availability triggers the decomposition of plant litter and assimilation of nitrogen by an ectomycorrhizal fungus (submitted)
Project description:Young Fagus sylvatica trees (approximately 7 to 8 years) were collected from a natural regeneration beech forest. The trees were excavated with intact soil cores, roots and top organic layer. The trees were then kept outdoors at the Department of Forest Botany, Georg-August-Universität Göttingen. Plants were protected from rain, and light conditions were matched to those of the natural stand using a shading net; otherwise, plants were exposed to natural climatic conditions. The soil moisture was regularly measured; plants were watered with deionized water as needed to keep soil moisture close to the original conditions. Trees was randomly relocated on a weekly basis throughout the experiment to avoid biasses caused by location or light effects. After 21 weeks, a treatment was applied to understand the physiological mechanisms of inorganic nitrogen uptake and assimilation under conditions of an inorganic nitrogen saturated forest simulation: Plants were fertilized with either a 20 mM solution of KNO3, a 20 mM solution of NH4Cl, or demineralized water (control) for 2 days. On the third day, the trees were harvested. Root tips were immediately shock-frozen in liquid nitrogen and used for RNA extraction.
Project description:Abstract: A large part of the nitrogen in forest soils is found in recalcitrant organic matter-protein complexes. Ectomycorrhizal fungi are thought to have a key role in the decomposition and mobilization of nitrogen from such complexes. The knowledge on the functional mechanisms of these processes, and how they are regulated by carbon from the host plant and the availability of more easily available forms of nitrogen sources are limited. We used spectroscopic analyses and transcriptome profiling to examine how the presence/absence of glucose and ammonium regulates the decomposition and mobilization of nitrogen from litter material by the ectomycorrhizal fungus Paxillus involutus. Amendments of glucose triggered the assimilation of nitrogen and the decomposition of the litter material. Concomitantly, the expression of genes encoding enzymes involved in oxidative (i.e. Fenton chemistry) degradation of polysaccharides and polyphenols, peptidases, nitrogen transporters and enzymes in pathways of the nitrogen and carbon metabolism were upregulated in concert. Addition of ammonium had minute effects on both the expression of transcripts and decomposition of litter material, and only when glucose was present. Based on the spectroscopic analyses, three major types of chemical modifications of the litter material were observed. Each of them was correlated with the expression of specific sets of genes encoding extracellular enzymes. Our data suggests that the expression of the decomposition and nitrogen assimilation machinery of ectomycorrhizal fungi can be firmly regulated by the host carbon supply, i.e. priming, and that the availability of inorganic nitrogen as such has limited effects on the saprotrophic activities. Rineau F, Shah F., Smits M.M., Persson P., Johansson T., Carleer R., Troein C., Tunlid A. (2013) Carbon availability triggers the decomposition of plant litter and assimilation of nitrogen by an ectomycorrhizal fungus (submitted) A one-chip study (data from 12 subarrays collected from a 12-plex Nimblegen microarray (ID 467991) using total RNA recovered from three separate glass-bead cultures of Paxillus involutus (ATCC200175) after amendments of various soil-derived substrates. Transcriptome profiling to examine how the presence/absence of glucose and ammonium regulates the decomposition and mobilization of nitrogen from litter material by the ectomycorrhizal fungus Paxillus involutus.
Project description:Plants aquire nitrogen from the soil, most commonly in the form of either nitrate or ammonium. Unlike ammonium, nitrate must be reduced (with NADH and ferredoxin as electron donors) prior to assimilation. Thus, nitrate nutrition imposes a substantially greater energetic cost than ammonium nutrition. Our goal was to compare the transcriptomes of nitrate-supplied and ammonium-supplied plants, with a particular interest in characterizing the differences in redox metabolism elicited by different forms of inorganic nitrogen. We used microarrays to compare the short-term transcriptional response to either nitrogen supply or ammonium supply in Arabidopsis roots. Genes upregulated or downregulated by nitrate only, ammonium only, or both ammonium and nitrate were identified and analyzed. Arabidopsis thaliana (Col-0) plants were grown hydroponically until they reached growth stage 5.10. They were then transferred to a nitrogen-free medium for 26 hr and then supplied with 1 mM nitrate or 1 mM ammonium. RNA isolation (and subsequent microarray analysis) was performed on root tissue isolated just before nitrogen supply (time 0) and at 1.5 hr and 8 hr after nitrogen supply (1.5 hr nitrate, 8 hr nitrate, 1.5 hr ammonium, 8 hr ammonium).