A Nodule-Specific Dicarboxylate Transporter from Alder Is a Member of the Peptide Transporter Family

Abstract

Alder (Alnus glutinosa) and more than 200 angiosperms that encompass 24 genera are collectively called actinorhizal plants. These plants form a symbiotic relationship with the nitrogen-fixing actinomycete Frankia strain HFPArI3. The plants provide the bacteria with carbon sources in exchange for fixed nitrogen, but this metabolite exchange in actinorhizal nodules has not been well defined. We isolated an alder cDNA from a nodule cDNA library by differential screening with nodule versus root cDNA and found that it encoded a transporter of the PTR (peptide transporter) family, AgDCAT1. AgDCAT1 mRNA was detected only in the nodules and not in other plant organs. Immunolocalization analysis showed that AgDCAT1 protein is localized at the symbiotic interface. The AgDCAT1 substrate was determined by its heterologous expression in two systems. Xenopus laevis oocytes injected with AgDCAT1 cRNA showed an outward current when perfused with malate or succinate, and AgDCAT1 was able to complement a dicarboxylate uptake-deficient Escherichia coli mutant. Using the E. coli system, AgDCAT1 was shown to be a dicarboxylate transporter with a K m of 70 m for malate. It also transported succinate, fumarate, and oxaloacetate. To our knowledge, AgDCAT1 is the first dicarboxylate transporter to be isolated from the nodules of symbiotic plants, and we suggest that it may supply the intracellular bacteria with dicarboxylates as carbon sources.Some plants and microorganisms engage in reciprocal symbiosis for the purpose of exchanging nutrients. For example, in nitrogen-fixing nodules, the intracellular bacteria supply the host plant with combined nitrogen and are in turn provided with carbon sources (Mylona et al., 1995). There are two types of nodule symbioses between nitrogen-fixing soil bacteria and higher plants, namely, the symbiosis between legumes and rhizobia, and the actinorhizal symbiosis between actinomycetes of the genus Frankia and a diverse group of angiosperms collectively called actinorhizal plants. In both cases, nutrient exchange between the host and its microsymbiont is controlled by the plant plasma membrane-derived interface enclosing the microsymbiont. In most legume symbioses, where the bacteria are taken up into the plant cells in a complete endocytotic process (Verma, 1992), this interface is the peribacteroid membrane (PBM). In primitive legume symbioses (de Faria et al., 1987) and the actinorhizal symbioses (Mylona et al., 1995), the interface is reported to be the invaginated and incompletely enclosed plasma membrane of the infected cell.The nutrient exchange between the symbiotic partners requires transporters of the carbon sources and trace elements that flow from the plant to the microsymbiont along with the transporters of the products of bacterial nitrogen fixation that flow from the microsymbiont to the plant (Pawlowski and Bisseling, 1996). Soybean (Glycine max) nodules, which represent legume symbioses, show evidence of the physiological or biochemical activities of transporters of ammonium, which i...

Transcriptomics of Actinorhizal Symbioses Reveals Homologs of the Whole Common Symbiotic Signaling Cascade

“…Around 1,500 unigenes (11%) for A. glutinosa and 2,000 unigenes (14%) for C. glauca were shown to be regulated or specifically induced during nodule development. In both species, it is worth noting that among the most highly induced genes (Table III), two previously characterized actinorhizal nodulins, a subtilase (Ag12/Cg12) and a dicarboxylate transporter (Agdcta1; Ribeiro et al, 1995;Laplaze et al, 2000;Svistoonoff et al, 2003;Jeong et al, 2004), were identified. More detailed data analysis enabled us to identify other known A. glutinosa nodulins with homologs in C. glauca.…”

“…On the other hand, a number of genes have been shown to be up-regulated in response to interaction with Frankia (Pawlowski, 2009). These genes include an enolase (van Ghelue et al, 1996), a subtilisin-like protease (Laplaze et al, 2000), a dicarboxylate transporter (Jeong et al, 2004), and nitrogen assimilation genes (Guan et al, 1996) as well as numerous poorly characterized genes.…”

Identification of arbuscular mycorrhiza-inducible Nitrate Transporter 1/Peptide Transporter Family (NPF) genes in rice

“…Recently, the Arabidopsis NPF7.3/NRT1.5 was shown to be a K + transporter and to NO 3 − -dependently control K + homeostasis in shoots (Drechsler et al 2015;Li et al 2017). Other family members, for example, function as a NO 3 − excretion transporter or in actinorhizal and rhizobial N-fixing symbioses (Jeong et al 2004;Segonzac et al 2007;Yendrek et al 2010), whereas a role of NPF proteins in plant-AMF interactions has not been observed yet.…”

Functional Assessment of the Medicago truncatula NIP/LATD Protein Demonstrates That It Is a High-Affinity Nitrate Transporter

“…NRT1(PTR) is a large family of transporters, comprising 53 members in Arabidopsis (Arabidopsis thaliana), 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 transporting NO 3 2 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 compared with the large number that exist in higher plants; thus, the number of biochemical functions ascribed to this family may expand.…”