The Response of Diatom Central Carbon Metabolism to Nitrogen Starvation Is Different from That of Green Algae and Higher Plants  

Abstract

The availability of nitrogen varies greatly in the ocean and limits primary productivity over large areas. Diatoms, a group of phytoplankton that are responsible for about 20% of global carbon fixation, respond rapidly to influxes of nitrate and are highly successful in upwelling regions. Although recent diatom genome projects have highlighted clues to the success of this group, very little is known about their adaptive response to changing environmental conditions. Here, we compare the proteome of the marine diatom Thalassiosira pseudonana (CCMP 1335) at the onset of nitrogen starvation with that of nitrogen-replete cells using two-dimensional gel electrophoresis. In total, 3,310 protein spots were distinguishable, and we identified 42 proteins increasing and 23 decreasing in abundance (greater than 1.5-fold change; P , 0.005). Proteins involved in the metabolism of nitrogen, amino acids, proteins, and carbohydrates, photosynthesis, and chlorophyll biosynthesis were represented. Comparison of our proteomics data with the transcriptome response of this species under similar growth conditions showed good correlation and provided insight into different levels of response. The T. pseudonana response to nitrogen starvation was also compared with that of the higher plant Arabidopsis (Arabidopsis thaliana), the green alga Chlamydomonas reinhardtii, and the cyanobacterium Prochlorococcus marinus. We have found that the response of diatom carbon metabolism to nitrogen starvation is different from that of other photosynthetic eukaryotes and bears closer resemblance to the response of cyanobacteria.

Transcript level coordination of carbon pathways during silicon starvation‐induced lipid accumulation in the diatom Thalassiosira pseudonana

“…Nutrient stress in diatoms induces changes in transcript abundances and can cause dramatic shifts in cellular health and physiology (Allen et al ., 2008; Mock et al ., 2008; Dyhrman et al ., 2012; Hockin et al ., 2012; Bender et al ., 2014; Abida et al ., 2015). Studies aimed at elucidating changes in transcript abundance during nutrient‐limited lipid accumulation often use nitrogen as the limiting nutrient, which is a stressful condition and induces massive cellular changes such as chlorosis and an associated down‐regulation of photosynthesis (Sun et al ., 2013; Abida et al ., 2015; Levitan et al ., 2015).…”

“…Advances in high‐throughput sequencing have facilitated culture‐based transcriptomic studies in diatoms, providing insight into the adaptive response of these organisms to environmental change, such as high light (Park et al ., 2010), carbon dioxide (Hennon et al ., 2015), phosphorus stress (Dyhrman et al ., 2012), nitrogen and silicon limitation and release (Mock et al ., 2008; Sapriel et al ., 2009; Hockin et al ., 2012; Shrestha et al ., 2012; Bender et al ., 2014), iron starvation (Allen et al ., 2008), and other stressors (Maheswari et al ., 2010). A more complete understanding of the significance of transcriptional control of cellular processes is important for an improved understanding of the basic biology of diatoms and other microalgae, and has implications for environmental and biotechnological studies.…”

“…Silicon is required for cell wall synthesis and growth in most diatoms, and silicon starvation also induces growth arrest and the formation of lipid droplets (Shifrin & Chisholm, 1981; Roessler, 1988; Traller & Hildebrand, 2013). In contrast to nitrogen starvation (Gasch et al ., 2000; Hockin et al ., 2012; Bender et al ., 2014), silicon starvation has little effect on overall metabolic activities, making it a unique approach to distinguish between cell cycle arrest and secondary effects that arise during nutrient limitation (Darley & Volcani, 1969; Claquin et al ., 2002). …”

Glucose Elevates NITRATE TRANSPORTER2.1 Protein Levels and Nitrate Transport Activity Independently of Its HEXOKINASE1-Mediated Stimulation of NITRATE TRANSPORTER2.1 Expression

“…Aliquots of 150 to 40 mg of seedling tissue were extracted according to Hockin et al (2012) with modifications. Tissue was ground at 270°C in a ball mill, and 60 mL of buffer containing 20 mM HEPES (pH 7.0), 5 mM EDTA, 10 mM NaF, and 250 mL of chloroform:methanol (1.5:3.5, v/v) was added.…”

Nitrate Reductase Knockout Uncouples Nitrate Transport from Nitrate Assimilation and Drives Repartitioning of Carbon Flux in a Model Pennate Diatom

“…Much recent work has focused both on characterizing the genes and metabolic pathways that induce lipid biosynthesis and on identifying routes and regulators that could be harnessed to substantially increase TAG production without negatively affecting growth (Alipanah et al, 2015;Ge et al, 2014;Hildebrand et al, 2012;Levitan et al, 2015;Radakovits et al, 2010;Trentacoste et al, 2013;Yang et al, 2013;Yoon et al, 2012). Deleterious impacts of NO 3 2 depletion include reduction of photosynthetic capacity, C-fixation, and N-assimilation and cessation of growth (Alipanah et al, 2015;Bender et al, 2014;Hockin et al, 2012;Syrett et al, 1986;Turpin, 1991).…”