Nitrogen (N) is an essential macronutrient that supports life in all living beings as a fundamental constituent of biomolecules, such as proteins and nucleic acids. Our goal in this research line is to understand N assimilation and its metabolism as well as its dissimilation in Chlamydomonas reinhardtii. Regarding N assimilation, we are trying to understand the molecular networks underlying the hierarchical preferences of this alga for different N sources (ammonium > nitrate/nitrite > organic nitrogen). Ammonium represses the assimilation of both nitrate and organic forms. But also nitrate represses the assimilation of organic N. Part of our work is oriented toward the identification of new molecular players that regulate these hierarchical relationships.  

 

   We are also interested in understanding nitric oxide (NO) metabolism and nitrate/nitrite dissimilation (or denitrification). Nitrate flux toward its assimilation is the predominant pathway under optimal conditions in Chlamydomonas as well as in other eukaryotic organisms containing an assimilatory nitrate reductase (NR). However, NR can also interact with the Molybdoenzyme NOFNIR (NO Forming Nitrite Reductase, aka. ARC) and reduce nitrite to NO, which is a signal molecule involved in the regulation of a wide variety of cellular processes, including nitrogen assimilation. Although NR is the main NO source in photosynthetic organisms, our group is also studying other NO sources that could have a prominent role under specific environmental conditions. Related to NO degradation, our group has also identified enzymes responsible for NO scavenging (called truncated hemoglobins, THBs) that convert NO into nitrate. Altogether, these enzymes constitute the nitrate-nitrate cycle whose functionality under physiological conditions has been poorly studied. 

 

   Alternatively, NO can also be reduced to nitrous oxide (N2O), which is a potent greenhouse gas. N2O production and release are mainly mediated by two proteins with NO-reductase activity located in mitochondria (CYP55) and chloroplast (FLV). Our group is trying to understand the physiological condition in which N2O is produced and released and how its synthesis is regulated. This knowledge will be important to elucidate whether large-scale microalgal cultivation could represent a source of N2O under conditions used in industry.