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Plant nitrate transporters in the NPF (NRT1) family are characterized by multifunctionality and their involvement in a number of physiological processes. The proteins in this family have been identified in many monocotyledonous and dicotyledonous species: a bioinformatic analysis predicts from 20 to 139 members in the plant genomes sequenced so far, including mosses. Plant NPFs are phylogenetically related to proton-coupled oligopeptide transporters, which are evolutionally conserved in all kingdoms of life apart from Archaea. The phylogenetic analysis of the plant NPF family is based on the amino acid sequences present in databases; an analysis identified a separate NPF6 clade (subfamily) with the first plant nitrate transporters studied at the molecular level. The available information proves that proteins of the NPF6 clade play key roles not only in the supply of nitrate and its allocation within different parts of plants but also in the transport of chloride, amino acids, ammonium, and plant hormones such as auxins and ABA. Moreover, members of the NPF6 family participate in the perception of nitrate and ammonium, signaling, plant responses to different abiotic stresses, and the development of tolerance to these stresses and contribute to the structure of the root-soil microbiome composition. The available information allows us to conclude that NPF6 genes are among the promising targets for engineering/editing to increase the productivity of crops and their tolerance to stresses. The present review summarizes the available published data and our own results on members of the NPF6 clade of nitrate transporters, especially under salinity; we outline their molecular, structural, and functional characteristics and suggest potential lines for future research.

The mammalian protein prestin is expressed in the lateral membrane wall of the cochlear hair outer cells and is responsible for the electromotile response of the basolateral membrane, following hyperpolarisation or depolarisation of the cells. Its impairment marks the onset of severe diseases, like non-syndromic deafness. Several studies have pointed out possible key roles of residues located in the Transmembrane Domain (TMD) that differentiate mammalian prestins as incomplete transporters from the other proteins belonging to the same solute-carrier (SLC) superfamily, which are classified as complete transporters. Here, we exploit the homology of a prototypical incomplete transporter (rat prestin, rPres) and a complete transporter (zebrafish prestin, zPres) with target structures in the outward open and inward open conformations. The resulting models are then embedded in a model membrane and investigated via a rigorous molecular dynamics simulation protocol. The resulting trajectories are analyzed to obtain quantitative descriptors of the equilibration phase and to assess a structural comparison between proteins in different states, and between different proteins in the same state. Our study clearly identifies a network of key residues at the interface between the gate and the core domains of prestin that might be responsible for the conformational change observed in complete transporters and hindered in incomplete transporters. In addition, we study the pathway of Cl- ions in the presence of an applied electric field towards their putative binding site in the gate domain. Based on our simulations, we propose a tilt and shift mechanism of the helices surrounding the ion binding cavity as the working principle of the reported conformational changes in complete transporters.

The NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER FAMILY ( NPF ) genes, initially characterized as nitrate or peptide transporters in plants, are involved in the transport of a large variety of substrates, including amino acids, nitrate, auxin (IAA), jasmonates (JAs), abscisic acid (ABA) and gibberellins (GAs) and glucosinolates. A total of 169 potential functional NPF genes were excavated in Brassica napus , and they showed diversified expression patterns in 90 different organs or tissues based on transcriptome profile data. The complex time-serial expression changes were found for most functional NPF genes in the development process of leaves, silique walls and seeds, which indicated that the expression of Brassica napus NPF ( BnaNPF ) genes may respond to altered phytohormone and secondary metabolite content through combining with promoter element enrichment analysis. Furthermore, many BnaNPF genes were detected to respond to vernalization with two different patterns, and 20 BnaNPF genes responded to nitrate deficiency. These results will provide useful information for further investigation of the biological function of BnaNPF genes for growth and development in rapeseed.

Nitrogen (N) is an essential macronutrient for plant growth. Plants absorb and utilize N mainly in the form of nitrate (NO 3 - ) or ammonium (NH 4 + ). In this study, the nitrate transporter DsNRT3.1 (also known as the nitrate assimilation-related protein DsNAR2.1) was characterized from Dianthus spiculifolius . A quantitative PCR (qPCR) analysis showed that the DsNRT3.1 expression was induced by NO 3 - . Under N-starvation conditions, the transformed Arabidopsis seedlings expressing DsNRT3.1 had longer roots and a greater fresh weight than the wild type. Subcellular localization showed that DsNRT3.1 was mainly localized to the plasma membrane in Arabidopsis root hair cells. Non-invasive micro-test (NMT) monitoring showed that the root hairs of N-starved transformed Arabidopsis seedlings had a stronger NO 3 - and NH 4 + influx than the wild-type seedlings, using with NO 3 - or NH 4 + as the sole N source; contrastingly, transformed seedlings only had a stronger NO 3 - influx when NO 3 - and NH 4 + were present simultaneously. In addition, the qPCR analysis showed that the expression of AtNRT2 genes ( AtNRT2.1 -2.6 ), and particularly of AtNRT2.5 , in the transformed Arabidopsis differed from that in the wild type. Overall, our results suggest that the heterologous expression of DsNRT3.1 affects seedlings' growth by enhancing the NO 3 - and NH 4 + uptake in N-starved Arabidopsis . This may be related to the differential expression of AtNRT2 genes.

One of the most important adaptations of seagrasses during sea colonization was the capacity to grow at the low micromolar nitrate concentrations present in the sea. In contrast to terrestrial plants that use H + symporters for high-affinity NO 3 - uptake, seagrasses such as Zostera marina L. use a Na + -dependent high-affinity nitrate transporter. Interestingly, in the Z. marina genome, only one gene ( Zosma70g00300.1 ; NRT2.1 ) is annotated to this function. Analysis of this sequence predicts the presence of 12 transmembrane domains, including the MFS domains of the NNP transporter family and the "nitrate signature" that appears in all members of the NNP family. Phylogenetic analysis shows that this sequence is more related to NRT2.5 than to NRT2.1, sharing a common ancestor with both monocot and dicot plants. Heterologous expression of ZosmaNRT2-GFP together with the high-affinity nitrate transporter accessory protein ZosmaNAR2 ( Zosma63g00220.1 ) in Nicotiana benthamiana leaves displayed four-fold higher fluorescence intensity than single expression of ZosmaNRT2-GFP suggesting the stabilization of NRT2 by NAR2. ZosmaNRT2-GFP signal was present on the Hechtian-strands in the plasmolyzed cells, pointing that ZosmaNRT2 is localized on the plasma membrane and that would be stabilized by ZosmaNAR2. Taken together, these results suggest that Zosma70g00300.1 would encode a high-affinity nitrate transporter located at the plasma membrane, equivalent to NRT2.5 transporters. These molecular data, together with our previous electrophysiological results support that ZosmaNRT2 would have evolved to use Na + as a driving ion, which might be an essential adaptation of seagrasses to colonize marine environments.

The NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family (NPF) proteins play important roles in moving substrates such as nitrate, peptides, amino acids, dicarboxylates, malate, glucosinolates, indole acetic acid (IAA), abscisic acid (ABA), and jasmonic acid. Although a unified nomenclature of NPF members in plants has been reported, this gene family has not been studied as thoroughly in apple ( Malus × domestica Borkh.) as it has in other species. Our objective was to provide general information about apple MdNPF s and analyze the transcriptional responses of some members to different levels of nitrate supplies. We identified 73 of these genes from the apple genome and used phylogenetic analysis to organize them into eight major groups. These apple NPFs are structurally conserved, based on alignment of amino acid sequences and analyses of phylogenetics and conserved domains. Examination of their genomic structures indicated that these genes are highly conserved among other species. We monitored 14 cloned MdNPF s that showed varied expression patterns under different nitrate concentrations and in different tissues. Among them, NPF6.5 was significantly induced by both low and high levels of nitrate. When compared with the wild type, 35S:MdNPF6.5 transgenic apple calli were more tolerant to low-N stress, which demonstrated that this gene confers greater capacity for nitrogen uptake under those conditions. We also analyzed the expression patterns of those 73 genes in various tissues. Our findings benefit future research on this family of genes.