Nramp: Deprive and conquer?

Solute carriers 11 (Slc11) evolved from bacterial permease (MntH) to eukaryotic antibacterial defense (Nramp) while continuously mediating proton (H+)-dependent manganese (Mn2+) import. Also, Nramp horizontal gene transfer (HGT) toward bacteria led to mntH polyphyly. Prior demonstration that evolutionary rate-shifts distinguishing Slc11 from outgroup carriers dictate catalytic specificity suggested that resolving Slc11 family tree may provide a function-aware phylogenetic framework. Hence, MntH C (MC) subgroups resulted from HGTs of prototype Nramp (pNs) parologs while archetype Nramp (aNs) correlated with phagocytosis. PHI-Blast based taxonomic profiling confirmed MntH B phylogroup is confined to anaerobic bacteria vs. MntH A (MA)'s broad distribution; suggested niche-related spread of MC subgroups; established that MA-variant MH, which carries 'eukaryotic signature' marks, predominates in archaea. Slc11 phylogeny shows MH is sister to Nramp. Site-specific analysis of Slc11 charge network known to interact with the protonmotive force demonstrates sequential rate-shifts that recapitulate Slc11 evolution. 3D mapping of similarly coevolved sites across Slc11 hydrophobic core revealed successive targeting of discrete areas. The data imply that pN HGT could advantage recipient bacteria for H+-dependent Mn2+ acquisition and Alphafold 3D models suggest conformational divergence among MC subgroups. It is proposed that Slc11 originated as a bacterial stress resistance function allowing Mn2+-dependent persistence in conditions adverse for growth, and that archaeal MH could contribute to eukaryogenesis as a Mn2+ sequestering defense perhaps favoring intracellular growth-competent bacteria.

Structure and function of the vacuolar Ccc1/VIT1 family of iron transporters and its regulation in fungi.

Iron is an essential micronutrient for most living beings since it participates as a redox active cofactor in many biological processes including cellular respiration, lipid biosynthesis, DNA replication and repair, and ribosome biogenesis and recycling. However, when present in excess, iron can participate in Fenton reactions and generate reactive oxygen species that damage cells at the level of proteins, lipids and nucleic acids. Organisms have developed different molecular strategies to protect themselves against the harmful effects of high concentrations of iron. In the case of fungi and plants, detoxification mainly occurs by importing cytosolic iron into the vacuole through the Ccc1/VIT1 iron transporter. New sequenced genomes and bioinformatic tools are facilitating the functional characterization, evolution and ecological relevance of metabolic pathways and homeostatic networks across the Tree of Life. Sequence analysis shows that Ccc1/VIT1 homologs are widely distributed among organisms with the exception of animals. The recent elucidation of the crystal structure of a Ccc1/VIT1 plant ortholog has enabled the identification of both conserved and species-specific motifs required for its metal transport mechanism. Moreover, recent studies in the yeast Saccharomyces cerevisiae have also revealed that multiple transcription factors including Yap5 and Msn2/Msn4 contribute to the expression of CCC1 in high-iron conditions. Interestingly, Malaysian S. cerevisiae strains express a partially functional Ccc1 protein that renders them sensitive to iron. Different regulatory mechanisms have been described for non-Saccharomycetaceae Ccc1 homologs. The characterization of Ccc1/VIT1 proteins is of high interest in the development of biofortified crops and the protection against microbial-derived diseases.

Iron deficiency triggered transcriptome changes in bread wheat.

A series of complex transport, storage and regulation mechanisms control iron metabolism and thereby maintain iron homeostasis in plants. Despite several studies on iron deficiency responses in different plant species, these mechanisms remain unclear in the allohexaploid wheat, which is the most widely cultivated commercial crop. We used RNA sequencing to reveal transcriptomic changes in the wheat flag leaves and roots, when subjected to iron limited conditions. We identified 5969 and 2591 differentially expressed genes (DEGs) in the flag leaves and roots, respectively. Genes involved in the synthesis of iron ligands i.e., nicotianamine (NA) and deoxymugineic acid (DMA) were significantly up-regulated during iron deficiency. In total, 337 and 635 genes encoding transporters exhibited altered expression in roots and flag leaves, respectively. Several genes related to MAJOR FACILITATOR SUPERFAMILY (MFS), ATP-BINDING CASSETTE (ABC) transporter superfamily, NATURAL RESISTANCE ASSOCIATED MACROPHAGE PROTEIN (NRAMP) family and OLIGOPEPTIDE TRANSPORTER (OPT) family were regulated, indicating their important roles in combating iron deficiency stress. Among the regulatory factors, the genes encoding for transcription factors of BASIC HELIX-LOOP-HELIX (bHLH) family were highly up-regulated in both roots and the flag leaves. The jasmonate biosynthesis pathway was significantly altered but with notable expression differences between roots and flag leaves. Homoeologs expression and induction bias analysis revealed subgenome specific differential expression. Our findings provide an integrated overview on regulated molecular processes in response to iron deficiency stress in wheat. This information could potentially serve as a guideline for breeding iron deficiency stress tolerant crops as well as for designing appropriate wheat iron biofortification strategies.