Poster: Membrane Transport

Abs # 1218: Physiological impact of CHL1 and AtNRT1:2 in Arabidopsis

Presenter:	Hu, Heng-Cheng , alvishu@gate.sinica.edu.tw
Authors	Hu, Heng-Cheng  (A)   Tsay, Yi-Fang  (A)
Affiliations:	(A): Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan

For most of plants, nitrate is their primary nitrogen source. Arabidopsis nitrate transporter gene CHL1 was isolated from a T-DNA tagged, chlorate resistant mutant. Database search in Arabidopsis indicated that there are 52 CHL1 homologs including AtNRT1:2. Through the approaches of antisense, knock-out, in situ hybridization, promoter-GUS reporting assay as well as electrophysiological assay using Xenopus oocyte expression system, it was shown that both CHL1 and AtNRT1:2 are responsible for nitrate uptake. However, there are some different characteristics between CHL1 and AtNRT1:2: (1) CHL1 is a nitrate -inducible gene, while AtNRT1:2 is a constitutive gene. (2) CHL1 is a dual-affinity nitrate transporter, but AtNRT1:2 is a low-affinity nitrate transporter. (3) In mature root, CHL1 is expressed in cortex and epidermis, but AtNRT1:2 is expressed in root hair and epidermis. With the differences in their properties, nitrate taken up by CHL1 and AtNRT1:2 might have different impact on nitrogen assimilation and plant growth. To address this issue, we have isolated atnrt1:2 knock-out mutant. Using microarray analysis, gene expression pattern in chl1 deletion mutant and atnrt1:2 knock-out mutant were compared under various nitrogen condition. In addition, nitrate partition and nitrate assimilation rate will be compared between chl1 and atnrt1:2 using N¹⁵ labeled nitrate. These analysis will help us to understand the complex interaction among the nitrate transporter genes and their effect on nitrate assimilation and plant growth.