A. Quesada et al., 3 NRT2 GENES ARE DIFFERENTIALLY REGULATED IN CHLAMYDOMONAS-REINHARDTII, MGG. Molecular & general genetics, 258(4), 1998, pp. 373-377
Two new nitrate assimilation-related genes, Nrt-2;3 and Nar5, have bee
n identified in Chlamydomonas reinhardtii. The Nrt2;3 gene is a new me
mber of the Nrt2 family, encoding high-affinity nitrate (nitrite) tran
sporters. Like that of the nitrate assimilation genes, expression of t
he Nrt2;3 gene is down-regulated by ammonium and positively controlled
by Nit2, a regulatory locus specific for the pathway. The three Nrt2
genes of C. reinhardtii are differentially regulated by the nitrogen s
ource. Expression of Nrt2;3 and of Nrt2;1, a nitrate/nitrite-bispecifi
c transporter gene, was induced by nitrate and more efficiently by nit
rite. Accumulation of mRNA of Nrt2;2. the nitrate-specific transporter
gene, was only induced efficiently by nitrate. The Nar5 gene is locat
ed upstream of the Nrt2:3 genomic region and expression of its mRNA is
down-regulated by ammonium. The Nrt2;3 and Nar5 genes are overexpress
ed in a deletion mutant that lacks nitrate assimilation loci.