The Chlamydomonas reinhardtii Nar1 Gene Encodes a Chloroplast Membrane Protein Involved in Nitrite Transport

Abstract

A key step for nitrate assimilation in photosynthetic eukaryotes occurs within chloroplasts, where nitrite is reduced to ammonium, which is incorporated into carbon skeletons. The Nar1 gene from Chlamydomonas reinhardtii is clustered with five other genes for nitrate assimilation, all of them regulated by nitrate. Sequence analysis of genomic DNA and cDNA of Nar1 and comparative studies of strains having or lacking Nar1 have been performed. The deduced amino acid sequence indicates that Nar1 encodes a chloroplast membrane protein with substantial identity to putative formate and nitrite transporters in bacteria. Use of antibodies against NAR1 has corroborated its location in the plastidic membrane. Characterization of strains having or lacking this gene suggests that NAR1 is involved in nitrite transport in plastids, which is critical for cell survival under limiting nitrate conditions, and controls the amount of nitrate incorporated by the cells under limiting CO(2) conditions.

A Soluble Guanylate Cyclase Mediates Negative Signaling by Ammonium on Expression of Nitrate Reductase in Chlamydomonas

“…Lamattina et al (2003) suggested that changes in NR activity could be modulated by nitrite availability. When the plant is photosynthetically active, nitrite produced by NR is immediately taken up by the chloroplast and reduced to ammonium (Rexach et al, 2000). However, nitrite accumulation can be expected when photosynthetic activity is low, so that NR-mediated conversion of nitrite to NO could take place in these conditions (Lillo et al, 2003;Lea et al, 2004) and NO could then repress NIA1 transcription, the whole process forming a feedback loop.…”

Chloroplast nitrite uptake is enhanced in Arabidopsis PII mutants

“…take into Chlamydomas chloroplasts appears to be regulated only under certain conditions, i.e. limiting nitrogen and carbon supply [32].…”

High-CO2 Response Mechanisms in Microalgae

“…LCIA, or NAR1.2, is involved in the bicarbonate transport system in chloroplasts (Duanmu et al, 2009) but is not regulated by nitrogen availability, and has been identified as a low-CO 2 -inducible gene by expressed sequence tag (EST) analysis . However, NAR1 genes generally involve members of the formate/nitrite transporter family (Rexach et al, 2000). In fact, LCIA-expressing Xenopus oocytes display both low-affinity bicarbonate transport and high-affinity nitrite transport activities (Mariscal et al, 2006), suggesting that LCIA is involved in both bicarbonate uptake and nitrite uptake induced under low-CO 2 conditions.…”