The Chlamydomonas NRT2 genes and the complexity of the nitrate/nitrite transport control in a single cell

Aurora Galván, Vicente Mariscal, Jose J. Higuera, Anthony J. Miller, and Emilio Fernández

Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba. Campus de Rabanales, Edificio Severo Ochoa, 14071 Córdoba, SPAIN Crop Performance and Improvement Division, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK.

NRT2 proteins are related to the high affinity nitrate and/or nitrite transport. These transporters are typically proteins with 12-transmembrane spanning domains corresponding to the NNP (Nitrate/Nitrite Porter) family and MFS (Major Facilitator Superfamily). NRT2 genes seem to be almost ubiquitous in genomes from organisms able to assimilate nitrate like plants, algae, fungi, yeast and bacteria. Some NRT2 transporters require a NAR2 type auxiliary protein that has been identified in algae and plants and with an essential role in nitrate assimilation of high affinity nitrate transport. The requirement or not of a NAR2-type component for some NRT2 transporters allows their classification into two categories, single (NRT2) or two component (NRT2/NAR2) systems. The Chlamydomonas genome contains a single NAR2 gene but six NRT2 genes. Only NRT2.1 and NRT2.2 are NAR2-dependent and clustered within the same genomic region containing other essential genes for nitrate assimilation. In this study, we have completed the characterization of the NRT2 family in Chlamydomonas and performed physiological studies in strains carrying particular transporters. We have identified new nitrate and nitrite transport activities, determining the specific induction pattern and substrate specificity, trying to found a specific function for NRT2 genes.

e-mail address of presenting author: bb1gacea@uco.es