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[Research] [Publications][Members][Lab Information][Course]
Nitrate Uptake and Transport in Higher Plants
I. Functional genomic analysis of NRT1 genes in Arabidopsis
Under a lot of conditions, nitrogen is the major limiting factor for crop productivity. For most plants, nitrate is their primary nitrogen source. Nitrate taken into the plant can be assimilated right away in the root tissue, stored in the vacuole for future use, or transported to the leaf tissue and assimilated there.
As a first step toward elucidating the molecular mechanism and regulation of nitrate uptake and transport in Arabidopsis, we have identified nitrate transporters that participate in several steps of nitrate translocation. Briefly, our data indicate that 1) CHL1 (AtNRT1), a nitrate inducible gene, encodes a dual-affinity nitrate transporter involved in both low- and high- affinity nitrate uptake of Arabidopsis; 2) a CHL1 homolog AtNRT1:2 is a pure low-affinity transporter involved only in the constitutive phase of nitrate uptake; 3) AtNRT1:3 is responsible for loading nitrate into xylem for long-distance transport; 4) AtNRT1:4, expressed in leaf petiole and localized at prevacuolar compartment, is responsible for nitrate storage; and 5) AtNRT1:5, expressed in leaf vein and induced by stress, is likely involved in nitrate relocalization under stress.
Arabidopsis genome contains 53 CHL1 homologs. RT-PCR analysis indicated that at least 52 of them are functional genes. We will continue to elucidate the in vivo function of other CHL1 homologs and their impact on plant growth.
II. Regulatory mechanism of CHL1 function
Although nitrate is a critical signaling molecule in regulating plant growth, little is know about plant nitrate signaling at molecular level. CHL1, a dual-affinity nitrate transporter, is switched between high- and low-affinity modes by phosphorylation and dephosphorylation: When CHL1 is phosphorylated at threonine residue 101, it functions as a high-affinity transporter; when dephosphorylated, it functions as low-affinity nitrate transporter. This novel regulatory mechanism could serve as a fast adaptation process for plant to adjust their high- and low-affinity uptake capacity in response to environmental changes. We had set up a genetic screening to isolate genes involved in the signaling pathway regulating CHL1 phosphorylation. This will help us understand what kind of kinase and phospohotase are responsible for functional switch of CHL1, and how plant sustains life using this pathway.
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- E-mail: mbyftsay@ccvax.sinica.edu.tw
- Lab No ¡GN317
- Office TEL ¡G(02) 2789-9198
- Lab TEL ¡G(02) 2789-9198
