Functional Assessment of the Medicago truncatula NIP/LATD Protein Demonstrates That It Is a High-Affinity Nitrate Transporter Page: 906
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Functional Assessment of the Medicago truncatula
NIP/LATD Protein Demonstrates That It Is a
High-Affinity Nitrate Transporterl[W[OA]
Rammyani Bagchi2, Mohammad Salehin2, O. Sarah Adeyemo, Carolina Salazar, Vladimir Shulaev,
D. Janine Sherrier, and Rebecca Dickstein*
Department of Biological Sciences, University of North Texas, Denton, Texas 76203 (R.B., M.S., O.S.A., C.S., V.S., R.D.);
and Department of Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, Newark,
Delaware 19711 (D.J.S.)
The Medicago truncatula NIP/LATD (for Numerous Infections and Polyphenolics/Lateral root-organ Defective) gene encodes a
protein found in a clade of nitrate transporters within the large NRT1(PTR) family that also encodes transporters of dipeptides
and tripeptides, dicarboxylates, auxin, and abscisic acid. Of the NRT1(PTR) members known to transport nitrate, most are low-
affinity transporters. Here, we show that M. truncatula nip/latd mutants are more defective in their lateral root responses to
nitrate provided at low (250 p/M) concentrations than at higher (5 mM) concentrations; however, nitrate uptake experiments
showed no discernible differences in uptake in the mutants. Heterologous expression experiments showed that MtNIP/LATD
encodes a nitrate transporter: expression in Xenopus laevis oocytes conferred upon the oocytes the ability to take up nitrate from
the medium with high affinity, and expression of MtNIP/LATD in an Arabidopsis chll(nrtl.1) mutant rescued the chlorate
susceptibility phenotype. X. laevis oocytes expressing mutant Mtnip-1 and Mtlatd were unable to take up nitrate from the
medium, but oocytes expressing the less severe Mtnip-3 allele were proficient in nitrate transport. M. truncatula nip/latd
mutants have pleiotropic defects in nodulation and root architecture. Expression of the Arabidopsis NRT1.1 gene in mutant
Mtnip-1 roots partially rescued Mtnip-1 for root architecture defects but not for nodulation defects. This suggests that the
spectrum of activities inherent in AtNRT1.1 is different from that possessed by MtNIP/LATD, but it could also reflect
stability differences of each protein in M. truncatula. Collectively, the data show that MtNIP/LATD is a high-affinity nitrate
transporter and suggest that it could have another function.
All plants require nitrogen (N) as an essential nu-
trient and are able to acquire N from nitrate (NO3-)
and ammonium (NH4') in the soil. Nitrate acquisition
begins with its transport into root cells, accomplished
by NO3- transporters. Soil NO3- concentrations can
vary by 5 orders of magnitude (Crawford, 1995), and
to cope with the variability, plants have evolved both
high-affinity (HATS) and low-affinity (LATS) trans-
port systems. These are encoded by two gene families:
the phylogenetically distinct NRT1(PTR) and NRT2
families. Members of these families also participate in
the movement of NO3- throughout the plant and
within plant cells (Miller et al., 2007; Segonzac et al.,
2007; Tsay et al., 2007; Almagro et al., 2008; Lin et al.,
1 This work was supported by the National Science Foundation
(grant nos. IOS-0923756 to R.D. and IOS-0923668 to D.J.S.).
2 These authors contributed equally to the article.
* Corresponding author; e-mail email@example.com.
The author responsible for distribution of materials integral to the
findings presented in this article in accordance with the policy de-
scribed in the Instructions for Authors (www.plantphysiol.org) is:
Rebecca Dickstein (firstname.lastname@example.org).
[W] The online version of this article contains Web-only data.
[OA] Open Access articles can be viewed online without a subscrip-
2008; Fan et al., 2009; Li et al., 2010; Barbier-Brygoo
et al., 2011; Wang and Tsay, 2011; Xu et al., 2012).
Proteins in the Chloride Channel (CLC) transporter
family also transport NO3-; these transporters are
associated with cytosol-to-organelle NO3- movement
(Zifarelli and Pusch, 2010).
NRT1(PTR) is a large family of transporters, com-
prising 53 members in Arabidopsis (Arabidopsis thali-
ana), 84 members in rice (Oryza sativa), with NRT1
(PTR) members known in several other species (Tsay
et al., 2007; Zhao et al., 2010). In addition to trans-
porting NO3- coupled to H+ movement, members of
the NRT1(PTR) family have been found to transport
dipeptides or tripeptides, amino acids (Waterworth
and Bray, 2006), dicarboxylic acids (Jeong et al., 2004),
auxin (Krouk et al., 2010b), and/or abscisic acid
(Kanno et al., 2012). Only a small number of NRT1
(PTR) proteins have been functionally studied com-
pared with the large number that exist in higher
plants; thus, the number of biochemical functions as-
cribed to this family may expand.
Of the NRT1(PTR) members known to transport
NO3-, most are LATS transporters. An important ex-
ception is Arabidopsis NRT1.1(CHL1), a dual-affinity
transporter that is the most extensively studied NRT1
(PTR) protein. AtNRT1.1(CHL1) was identified initially
on the basis of its ability to confer chlorate toxicity
906 Plant Physiology, October 2012, Vol. 160, pp. 906-916, www.plantphysiol.org 2012 American Society of Plant Biologists. All Rights Reserved.
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Bagchi, Rammyani; Salehin, Mohammad; Adeyemo, O. Sarah; Salazar, Carolina; Shulaev, Vladimir; Sherrier, D. Janine et al. Functional Assessment of the Medicago truncatula NIP/LATD Protein Demonstrates That It Is a High-Affinity Nitrate Transporter, article, October 2012; [Rockville, Maryland]. (digital.library.unt.edu/ark:/67531/metadc130185/m1/1/: accessed January 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.