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Evolution of Electrogenic Ammonium Transporters (AMTs).

McDonald TR, Ward JM - Front Plant Sci (2016)

Bottom Line: The genomes of angiosperms contain genes for both electrogenic and electroneutral ammonium transporters, but it is not clear how far back in the land plant lineage electrogenic ammonium transporters occur.Here, we place Marchantia polymorpha ammonium transporters in the AMT/MEP/Rh phylogeny and we show that AMTs from the liverwort M. polymorpha are electrogenic.This information suggests that electrogenic ammonium transport evolved at least as early as the divergence of bryophytes in the land plant lineage.

View Article: PubMed Central - PubMed

Affiliation: Biology Department, St. Catherine University St. Paul, MN, USA.

ABSTRACT
The ammonium transporter gene family consists of three main clades, AMT, MEP, and Rh. The evolutionary history of the AMT/MEP/Rh gene family is characterized by multiple horizontal gene transfer events, gene family expansion and contraction, and gene loss; thus the gene tree for this family of transporters is unlike the organismal tree. The genomes of angiosperms contain genes for both electrogenic and electroneutral ammonium transporters, but it is not clear how far back in the land plant lineage electrogenic ammonium transporters occur. Here, we place Marchantia polymorpha ammonium transporters in the AMT/MEP/Rh phylogeny and we show that AMTs from the liverwort M. polymorpha are electrogenic. This information suggests that electrogenic ammonium transport evolved at least as early as the divergence of bryophytes in the land plant lineage.

No MeSH data available.


Related in: MedlinePlus

Electrogenic ammonium transport by AMTs from Marchantia polymorpha. MpAMT cDNAs were expressed Xenopus oocytes. The oocytes were bathed in K+-free ringer solution (pH 5.6), voltage clamped at −40 mV and substrates were applied where indicated. Concentrations of substrates were 300 μM except that 50 μM NH4Cl was used for MpAMT1.5. MACl is methyl ammonium chloride.
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Figure 4: Electrogenic ammonium transport by AMTs from Marchantia polymorpha. MpAMT cDNAs were expressed Xenopus oocytes. The oocytes were bathed in K+-free ringer solution (pH 5.6), voltage clamped at −40 mV and substrates were applied where indicated. Concentrations of substrates were 300 μM except that 50 μM NH4Cl was used for MpAMT1.5. MACl is methyl ammonium chloride.

Mentions: To determine whether M. polymorpha AMT transporters were indeed electrogenic, four of the five AMT cDNAs were cloned from the male Marchantia accession Tak-1 (Okada et al., 2000) and expressed in Xenopus oocytes. Two-electrode voltage clamping was used to measure substrate-induced currents. Perfusion of 300 μM NH4Cl over the oocytes expressing Marchantia ammonium transporters produced large inward currents consistent with an electrogenic mechanism of ammonium transport (Figure 4). Very large currents were produced in oocytes expressing MpAMT1;4 and MpAMT1;5. Therefore, to reduce the level of transport activity, MpAMT1;4 RNA was injected at a 30-fold lower concentration, and ammonium chloride was applied at a reduced concentration of 50 μM for oocytes expressing MpAMT1;5 (Figure 4). Methylammonium chloride induced small inward currents indicating that MpAMTs may have a higher affinity for ammonium compared to methyl ammonium. Potassium chloride induced small outward currents consistent with the activation of endogenous Na/K-ATPase activity. The results are consistent with a high selectivity of the MpAMTs for ammonium over K+. Under our recording conditions, no ammonium- or methylammonium-dependent currents were observed in uninjected oocytes (Figure 4). However, application of 300 μM KCl induced small outward currents also in uninjected oocytes indicating that the outward currents are not associated with expression of the MpAMTs (Figure 4). The results show that AMTs from the basal plant M. polymorpha are electrogenic. The results support the hypothesis that all plant ammonium transporters in the AMT clade (AMT1s) are electrogenic.


Evolution of Electrogenic Ammonium Transporters (AMTs).

McDonald TR, Ward JM - Front Plant Sci (2016)

Electrogenic ammonium transport by AMTs from Marchantia polymorpha. MpAMT cDNAs were expressed Xenopus oocytes. The oocytes were bathed in K+-free ringer solution (pH 5.6), voltage clamped at −40 mV and substrates were applied where indicated. Concentrations of substrates were 300 μM except that 50 μM NH4Cl was used for MpAMT1.5. MACl is methyl ammonium chloride.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814505&req=5

Figure 4: Electrogenic ammonium transport by AMTs from Marchantia polymorpha. MpAMT cDNAs were expressed Xenopus oocytes. The oocytes were bathed in K+-free ringer solution (pH 5.6), voltage clamped at −40 mV and substrates were applied where indicated. Concentrations of substrates were 300 μM except that 50 μM NH4Cl was used for MpAMT1.5. MACl is methyl ammonium chloride.
Mentions: To determine whether M. polymorpha AMT transporters were indeed electrogenic, four of the five AMT cDNAs were cloned from the male Marchantia accession Tak-1 (Okada et al., 2000) and expressed in Xenopus oocytes. Two-electrode voltage clamping was used to measure substrate-induced currents. Perfusion of 300 μM NH4Cl over the oocytes expressing Marchantia ammonium transporters produced large inward currents consistent with an electrogenic mechanism of ammonium transport (Figure 4). Very large currents were produced in oocytes expressing MpAMT1;4 and MpAMT1;5. Therefore, to reduce the level of transport activity, MpAMT1;4 RNA was injected at a 30-fold lower concentration, and ammonium chloride was applied at a reduced concentration of 50 μM for oocytes expressing MpAMT1;5 (Figure 4). Methylammonium chloride induced small inward currents indicating that MpAMTs may have a higher affinity for ammonium compared to methyl ammonium. Potassium chloride induced small outward currents consistent with the activation of endogenous Na/K-ATPase activity. The results are consistent with a high selectivity of the MpAMTs for ammonium over K+. Under our recording conditions, no ammonium- or methylammonium-dependent currents were observed in uninjected oocytes (Figure 4). However, application of 300 μM KCl induced small outward currents also in uninjected oocytes indicating that the outward currents are not associated with expression of the MpAMTs (Figure 4). The results show that AMTs from the basal plant M. polymorpha are electrogenic. The results support the hypothesis that all plant ammonium transporters in the AMT clade (AMT1s) are electrogenic.

Bottom Line: The genomes of angiosperms contain genes for both electrogenic and electroneutral ammonium transporters, but it is not clear how far back in the land plant lineage electrogenic ammonium transporters occur.Here, we place Marchantia polymorpha ammonium transporters in the AMT/MEP/Rh phylogeny and we show that AMTs from the liverwort M. polymorpha are electrogenic.This information suggests that electrogenic ammonium transport evolved at least as early as the divergence of bryophytes in the land plant lineage.

View Article: PubMed Central - PubMed

Affiliation: Biology Department, St. Catherine University St. Paul, MN, USA.

ABSTRACT
The ammonium transporter gene family consists of three main clades, AMT, MEP, and Rh. The evolutionary history of the AMT/MEP/Rh gene family is characterized by multiple horizontal gene transfer events, gene family expansion and contraction, and gene loss; thus the gene tree for this family of transporters is unlike the organismal tree. The genomes of angiosperms contain genes for both electrogenic and electroneutral ammonium transporters, but it is not clear how far back in the land plant lineage electrogenic ammonium transporters occur. Here, we place Marchantia polymorpha ammonium transporters in the AMT/MEP/Rh phylogeny and we show that AMTs from the liverwort M. polymorpha are electrogenic. This information suggests that electrogenic ammonium transport evolved at least as early as the divergence of bryophytes in the land plant lineage.

No MeSH data available.


Related in: MedlinePlus