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Nutrient-regulated transcriptional responses in the brown tide forming alga Aureococcus anophagefferens

ABSTRACT: Relatively little is known about the presence and regulation of pathways involved in nutrient acquisition in the brown tide forming alga, Aureococcus anophagefferens. In this study, Long-SAGE (Serial Analysis of Gene Expression) was used to profile the A. anophagefferens transcriptome under nutrient replete (control), and nitrogen (N) and phosphorus (P) deficiency with the goal of understanding how this organism responds at the transcriptional level to varying nutrient conditions. This approach has aided A. anophagefferens genome annotation efforts and identified a suite of genes up-regulated by N and P deficiency, some of which have known roles in nutrient metabolism. Genes up-regulated under N deficiency include an ammonium transporter, an acetamidase/formamidase, and two peptidases. This suggests an ability to utilize reduced N compounds and dissolved organic nitrogen, supporting the hypothesized importance of these N sources in A. anophagefferens bloom formation. There are also a broad suite of P-regulated genes, including an alkaline phosphatase, and two 5’-nucleotidases, suggesting A. anophagefferens may use dissolved organic phosphorus under low phosphate conditions. These N- and P-regulated genes may be important targets for exploring nutrient controls on bloom formation in field populations.

ORGANISM(S): Aureococcus anophagefferens

PROVIDER: GSE21465 | GEO | 2010/11/05

SECONDARY ACCESSION(S): PRJNA125815

REPOSITORIES: GEO

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Project description:Relatively little is known about the presence and regulation of pathways involved in nutrient acquisition in the brown tide forming alga, Aureococcus anophagefferens. In this study, Long-SAGE (Serial Analysis of Gene Expression) was used to profile the A. anophagefferens transcriptome under nutrient replete (control), and nitrogen (N) and phosphorus (P) deficiency with the goal of understanding how this organism responds at the transcriptional level to varying nutrient conditions. This approach has aided A. anophagefferens genome annotation efforts and identified a suite of genes up-regulated by N and P deficiency, some of which have known roles in nutrient metabolism. Genes up-regulated under N deficiency include an ammonium transporter, an acetamidase/formamidase, and two peptidases. This suggests an ability to utilize reduced N compounds and dissolved organic nitrogen, supporting the hypothesized importance of these N sources in A. anophagefferens bloom formation. There are also a broad suite of P-regulated genes, including an alkaline phosphatase, and two 5’-nucleotidases, suggesting A. anophagefferens may use dissolved organic phosphorus under low phosphate conditions. These N- and P-regulated genes may be important targets for exploring nutrient controls on bloom formation in field populations. Aureococcus anophagefferens CCMP 1984 was obtained from the Provasoli-Guillard Center for the Culture of Marine Phytoplankton (CCMP). The cultures were grown at 18C on a 14 h:10 h light:dark cycle (140 µmol quanta m-2 s-1). Nitrogen- and phosphate-replete (883 µM NO3- and 36.3 µM PO43-) cells, –N (40 µM NO3-) cells, and –P (1 µM PO43-) cells were grown in autoclaved L1 media with no Si (Guillard and Hargraves 1993), prepared using 0.2 µm filtered Vineyard Sound seawater. Vitamins (thiamine, biotin, and B12) were sterile filtered and added to the media after autoclaving. Replete cells were harvested during mid log phase of growth, while –N and –P cells were harvested at the onset of stationary phase when N or P was depleted.

Project description:Abiotic stress causes disturbances in the cellular homeostasis. Re-adjustment of balance in carbon, nitrogen and phosphorus metabolism therefore plays a central role in stress adaptation. However, it is currently unknown which parts of the primary cell metabolism follow common patterns under different stress conditions and which represent specific responses. To address these questions, changes in transcriptome, metabolome and ionome were analyzed in maize source leaves from plants suffering low temperature, low nitrogen (N) and low phosphorus (P) stress. The selection of maize as study object provided data directly from an important crop species and the so far underexplored C4 metabolism. Growth retardation was comparable under all tested stress conditions. The only primary metabolic pathway responding similar to all stresses was nitrate assimilation, which was down-regulated. The largest group of commonly regulated transcripts followed the expression pattern: down under low temperature and low N, but up under low P. Several members of this transcript cluster could be connected to P metabolism and correlated negatively to different phosphate concentration in the leaf tissue. Accumulation of starch under low temperature and low N stress, but decrease in starch levels under low under low P conditions indicated that only low P treated leaves suffered carbon starvation. In conclusion, maize employs very different strategies for management of nitrogen and phosphorus metabolism under stress. While nitrate assimilation was regulated depending on demand by growth processes, phosphate concentrations changed depending on availability, thus building up reserves under excess conditions. Carbon and energy metabolism of the C4 maize leaves were particularly sensitive to P starvation. Responses of maize source leaves to low temperature, low nitrogen and low phosphorus conditions were tested in independent single-stress experiments. Seedlings were cultivated in pots containing nutrient-poor peat soil under the controlled conditions of a growth chamber. The plants were fertilized with modified Hoagland solutions, containing 15mM KNO3 and 0.5mM KH2PO4 for control conditions; for low N and low P treatment, the nutrient concentrations were reduced to 0.15mM KNO3 and 0.1mM KH2PO4, respectively. Low temperature treated plants were always supplied with control nutrient solution. Plants from the nitrogen and phosphorus experiment as well as the control temperature plants were exposed to 28Â°C during the day and 20Â°C during the night. Low temperature treatment was limited to the night period and was reduced to 4Â°C for the 10h dark period. Source leaf lamina were harvested at day 20 (low temperature experiment) or day 30 after start of germination (low nitrogen and low phosphorus experiment) for parallel analysis of transcriptome, metabolome and ion profiles. The molecular data is further supplemented by phenotypic characterization of the maize seedlings under investigation.

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Nutrient-regulated transcriptional responses in the brown tide forming alga Aureococcus anophagefferens

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