Functional Characterization of the Tmg-4 Magnesium Transporter with the GQN Motif from Neurospora crassa

To unveil the physiological relevance of magnesium and its transport pathways in Neurospora crassa, the vegetative, asexual, and sexual phases of development were investigated. Notably, a regular rate of hyphal growth extension was observed in media without magnesium supplementation. Further, conidia and perithecia formation was completely abolished under the same conditions. By estimating the levels of mycelial cations, magnesium was identified as the 3rd most abundant ion and its transport was found to be mediated by four putative CorA magnesium transporters: Tmg-1, Tmg-2, Tmg-3, and Tmg-4. Among these, the Tmg-4 transporter encoded by the NCU07816.5 (tmg-4) gene possesses a GQN motif instead of the universally conserved GMN motif of CorA magnesium transporters. Phenotypic analysis of the knockout mutant strain, Δtmg-4, revealed stunted vegetative growth, acquired partial cobalt resistance, and reduced levels of mycelial magnesium compared to that of the wild type strain. Further, tmg-4 gene expression remained unchanged during vegetative development but was upregulated by three-fold in the sexual cycle. Collectively, these results validate tmg-4 and its encoded protein as functional novel variant in the CorA superfamily magnesium transporters of fungi.