Molecular and functional regulation of two NO3- uptake systems by N- and C-status of Arabidopsis thaliana

• Published in: The Plant journal : for cell and molecular biology Vol. 18; no. 5; pp. 509 - 519
• Main Authors: Lejay, L, Tillard, P, Lepetit, M, Olive, F.D, Filleur, S, Daniel-Vedele, F, Gojon, A
• Format: Journal Article
• Language: English
• Published: 01.06.1999
• Subjects: Arabidopsis thaliana; carbon; diurnal variation; feedback; gene expression; genotype; isotope labeling; metabolites; mutants; nitrates; nitrogen content; nutrient availability; nutrient solutions; nutrient uptake; nutrient-nutrient interactions; photosynthesis; plant proteins; regulation; roots; sucrose
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313X.1999.00480.x

Root NO(3)- uptake and expression of two root NO(3)- transporter genes (Nrt2;1 and Nrt1) were investigated in response to changes in the N- or C-status of hydroponically grown Arabidopsis thaliana plants. Expression of Nrt2;1 is up-regulated by NO(3)- starvation in wild-type plants and by N-limitation in a nitrate reductase (NR) deficient mutant transferred to NO(3)- as sole N source. These observations show that expression of Nrt2;1 is under feedback repression by N-metabolites resulting from NO(3)- reduction. Expression of Nrt1 is not subject to such a repression. However, Nrt1 is overexpressed in the NR mutant even under N-sufficient conditions (growth on NH(4)NO(3) medium), suggesting that expression of this gene is affected by the presence of active NR, but not by N-status of the plant. Root (15)NO(3)- influx is markedly increased in the NR mutant as compared to the wild-type. Nevertheless, both genotypes have similar net (15)NO(3)- uptake rates due to a much larger (14)NO(3)- efflux in the mutant than in the wild-type. Expressions of Nrt2;1 and Nrt1 are diurnally regulated in photosynthetically active A. thaliana plants. Both increase during the light period and decrease in the first hours of the dark period. Sucrose supply prevents the inhibition of Nrt2;1 and Nrt1 expressions in the dark. In all conditions investigated, Nrt2;1 expression is strongly correlated with root (15)NO(3)- influx at 0.2mM external concentration. In contrast, changes in the Nrt1 mRNA level are not always associated with similar changes in the activities of high- or low-affinity NO(3)- transport systems.