Nitrogen-dependent regulation of photosynthetic gene expression

Abstract

Nitrogen-limited Chlamydomonas reinhardtii is chlorotic and very deficient in chlorophyll a/b lightharvesting complexes (LHC). Rates of synthesis of photosynthetic proteins, but especially the LHC apoproteins, are reduced 10-to 40-fold. Moderately high levels of chloroplast transcripts accumulate in nitrogen-limited cells, and there is a correlation between chloroplast DNA levels and chloroplast mRNA abundance. In contrast, nuclear transcripts encoding LHCII and ribulose 1,5-bisphosphate carboxylase small subunits are markedly reduced. Thus, nitrogen availability affects chloroplast protein synthesis by inhibition of translation and, to a lesser extent, chloroplast DNA amplification. Regulation of nuclear-encoded photosynthetic proteins by nitrogen is achieved through mechanisms affecting transcription and/or mRNA stability.Nitrogen (N) assimilation, photosynthetic electron transport, and CO2 fixation are interwoven processes limiting plant growth. Reducing equivalents generated from photosynthetic electron transport are required for nitrate reduction, and ATP-dependent NH' assimilation into amino acids occurs primarily within plastids (1). In turn, amino acid recycling is integral to photorespiration (2). N availability not only restricts the photosynthetic efficiency of plants but also it appears to regulate photosynthate utilization. Typically, products such as starch, lipid, and carotenoids accumulate in N-deficient plants (3-7). Despite major effects of N on photosynthetic pigments, information on its role in the regulation of photosynthetic gene expression and the synthesis of photosynthetic proteins is meager (8-10). 2678 branes were prewashed [1 hr at 650C in 0.2x SSPE (lx SSPE = 0.15 M NaCl/50 mM Na2HPO4, pH 7.4/5 mM EDTA) containing 0.5% NaDodSO4], prehybridized (4 hr at 420C), and hybridized (24-48 hr at 420C) as described (14). Blots were washed twice for 30 min at 260C in 2x SSPE/0.1% NaDodSO4 and twice for 15 min at 50'C in 0.1x SSPE/0.1% NaDodSO4 and then were exposed to Kodak XAR film at -70'C without intensifying screens. Dextran sulfate was used with pHS16 (see below) (15). For dot blots, 50 /.d of equal amounts of RNA (adjusted with wheat-germ tRNA) were spotted onto Zeta Probe under low-vacuum conditions and processed as described above. MATERIALS AND METHODSSouthern Blot Analysis. DNA in the LiCI-soluble fraction of nucleic acid extracts was precipitated with ethanol and resuspended in water. DNA was digested with restriction enzymes (see the legend to Fig. 7), treated for 30 min at 37°C with boiled RNase at 30 ,g/ml, and resolved on agarose gels. Before transfer to GeneScreenPlus (DuPont), DNA was depurinated (0.2 M HCO for 5 min), denatured (1.5 M NaCl/0.5 M NaOH), and neutralized (3 M NaCl/0.5 M Tris, pH 7.0). Prehybridization and hybridization solutions were as above but with NaDodSO4 at 0.5%. For dot blots, equal amounts of DNA (adjusted with herring sperm DNA) were denatured (0.25 M NaOH for 10 min), neutralized, and applied to GeneScreenPlus (see above).DNA Probes. pHS16 recog...

Changes in Transcript Abundance in Chlamydomonas reinhardtii following Nitrogen Deprivation Predict Diversion of Metabolism

“…In C. reinhardtii, photosynthetic efficiency decreases following N deprivation, at least partially due to a reduction in the abundance of light-harvesting complexes (Plumley and Schmidt, 1989;Peltier and Schmidt, 1991) and selective degradation of the cytochrome b 6 f complex (Bulté and Wollman, 1992;Majeran et al, 2000). Likewise, the abundance of transcripts encoding photosynthesis-related proteins was substantially reduced following N deprivation.…”

Developmental regulation of photosynthate distribution in leaves of rice

“…We determined mRNA expression patterns under low and high N, because N application has been found to promote the expression of Rubisco (Plumley and Schmidt 1989), GS (Sakakibara et al 1992), and PEPC (Suzuki et al 1994). …”

Screening for hydrogen-producing strains of green microalgae in phosphorus or sulphur deprived medium under nitrogen limitation

“…Nitrogen deprivation is a severe stress condition for all organisms because nitrogen is a major component of proteins and nucleic acid. A limitation of nitrogen in Chlamydomonas cells resulted in lower cellular chlorophyll contents and LHCII levels 19 . The differences in pigmentation and antennae composition probably have an impact on light energy transfer to the photosystems 5 .…”