Characterization of the NRAMP Gene Family in the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis

Abstract

Transporters of the NRAMP family are ubiquitous metal-transition transporters, playing a key role in metal homeostasis, especially in Mn and Fe homeostasis. In this work, we report the characterization of the NRAMP family members (RiSMF1, RiSMF2, RiSMF3.1 and RiSMF3.2) of the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis. Phylogenetic analysis of the NRAMP sequences of different AM fungi showed that they are classified in two groups, which probably diverged early in their evolution. Functional analyses in yeast revealed that RiSMF3.2 encodes a protein mediating Mn and Fe transport from the environment. Gene-expression analyses by RT-qPCR showed that the RiSMF genes are differentially expressed in the extraradical (ERM) and intraradical (IRM) mycelium and differentially regulated by Mn and Fe availability. Mn starvation decreased RiSMF1 transcript levels in the ERM but increased RiSMF3.1 expression in the IRM. In the ERM, RiSMF1 expression was up-regulated by Fe deficiency, suggesting a role for its encoded protein in Fe-deficiency alleviation. Expression of RiSMF3.2 in the ERM was up-regulated at the early stages of Fe toxicity but down-regulated at later stages. These data suggest a role for RiSMF3.2 not only in Fe transport but also as a sensor of high external-Fe concentrations. Both Mn- and Fe-deficient conditions affected ERM development. While Mn deficiency increased hyphal length, Fe deficiency reduced sporulation.

Iron in the Symbiosis of Plants and Microorganisms

“…The genes encoding NRAMP family members RiSMF1 , RiSMF2 , RiSMF3.1 and RiSMF3.2 were characterized in Rhizophagus irregularis . In the complementary experiment of yeast fet3fet4 mutant, only RiSMF3.2 was proved to be an iron transporter [ 83 ].…”

Exploring the Roles of Arbuscular Mycorrhizal Fungi in Plant–Iron Homeostasis

“…Kabir et al [40] also found that AMF upregulate another ferric reductase gene, HaFRO1, alongside the expression of transport genes HaNramp1 and HaIRT1. Moreover, in the context of iron homeostasis, natural resistance-associated macrophage protein transporters also play a key role, and members, such as RiSMF1, RiSMF2, RiSMF3.1, and RiSMF3.2, have been identified in R. irregularis [20,44].…”