Plasticity of the mitoproteome to nitrogen sources (nitrate and ammonium) in Chlamydomonas reinhardtii: The logic of Aox1 gene localization

Abstract

Nitrate and ammonium constitute primary inorganic nitrogen sources that can be incorporated into carbon skeletons in photosynthetic eukaryotes. In Chlamydomonas, previous studies and the present one showed that the mitochondrial AOX is up-regulated in nitrate-grown cells in comparison with ammonium-grown cells. In this work, we have performed a comparative proteomic analysis of the soluble mitochondrial proteome of Chlamydomonas cells growth either on nitrate or ammonium. Our results highlight important proteomics modifications mostly related to primary metabolism in cells grown on nitrate. We could note an up-regulation of some TCA cycle enzymes and a down-regulation of cytochrome c1 together with an up-regulation of l-arginine and purine catabolism enzymes and of ROS scavenging systems. Hence, in nitrate-grown cells, AOX may play a dual role: (1) lowering the ubiquinone pool reduction level and (2) permitting the export of mitochondrial reducing power under the form of malate for nitrate and nitrite reduction. This role of AOX in the mitochondrial plasticity makes logical the localization of Aox1 in a nitrate assimilation gene cluster.

Combined intracellular nitrate and NIT2 effects on storage carbohydrate metabolism in Chlamydomonas

“…This inhibition was accompanied by a stimulation of acetate uptake and an unchanged dark respiration, except that the observed growth inhibition was due to slower acetate assimilation via the respiratory chain. The stimulation of acetate uptake and assimilation in the nia1 strain was supported by previous comparative proteomic data analysis of wild-type strains demonstrating that acetyl-coA synthases, key steps in the assimilation of acetate, are also upregulated in -grown compared with - grown cells (Gerin et al , 2010). …”

“…The tight control of C/N metabolism involves, besides sugar sensing and its signalling pathways, signals produced from , , and other N metabolites such as glutamate, glutamine, and aspartate (Stitt and Krapp, 1999; Coruzzi and Zhou, 2001; Miller et al , 2008). , for example, is not only an essential nutrient but also a key N signalling molecule, regulating the expression of genes involved in N assimilation and primary metabolism, as well as cellular and developmental processes (Scheible et al , 1997, 2004; Zhang and Forde, 1998; Wang et al , 2003; Gerin et al , 2010). …”

“…assimilation have been shown to be positively regulated by NIT2 , such as genes involved in uptake repression and induction, including NIA1 and NIR1 , encoding NR and NiR, respectively (Fernandez et al , 1989; Quesada et al , 1998 a ) and genes involved in N transport, such as NRT2;1 , NRT2;2 , NRT2;3 NAR2 , and NAR1 encoding /nitrite transporters (Quesada et al , 1998 b ; Rexach et al , 2000). Despite the role of on its own metabolism, it has also been demonstrated that the latter is involved in uptake and acetate assimilation by repressing NIA1 gene expression, and inducing acetyl-CoA synthetase, respectively (Llamas et al , 2002; Gerin et al , 2010). …”

Modeling the dependence of respiration and photosynthesis upon light, acetate, carbon dioxide, nitrate and ammonium in Chlamydomonas reinhardtiiusing design of experiments and multiple regression

“…Interestingly, the gene encoding AOX ( Aox1 ) is known to be located within a gene cluster which also encodes components of the nitrate assimilatory pathway and is tightly regulated by the nitrogen source [ 66 ]; consequently, AOX expression and capacity were shown to be induced by nitrate and repressed by ammonium in a concentration-dependent manner [ 61 ]. With regards to the peculiar genetic localization and regulation of Aox1 , the postulated role of mitochondrial respiration in nitrate assimilation was proposed to be essentially mediated by AOX, as also indicated by a recent comparative proteomic study published by our group [ 67 ]. The present results are in good agreement with these findings.…”

Cyclin-dependent Kinase E1 (CDKE1) Provides a Cellular Switch in Plants between Growth and Stress Responses

“…Tobacco suspension cells unable to induce AOX continue to grow under severe nutrient limiting conditions in contrast to cells that can induce AOX and essentially stop growing (56). Furthermore, in tobacco cells and Chlamydomonas reinhardtii, a lack of AOX results in larger cells (57,58). Thus the KIN10 and CDKE1/RAO1 interplay represents an efficient protein kinase signal cascade that essentially provides a mechanism by which plants can detect and integrate signals from multiple input sources, and switch between growth and stress responses.…”