Abstract
Bicarbonate (HCO3−) transporter family including the anion exchanger (AE) group is involved in multiple physiological processes through regulating acid-base homeostasis. HCO3− transporters have been extensively studied in mammals, but fungal homologues of AE are poorly understood. Here, we characterized the AE group member (MoAE4) in Magnaporthe oryzae. MoAE4 exhibits more sequence and structure homologies with the reported AE4 and BOR1 proteins. In addition to the common sublocalization on cytomembrane, MoAE4 also localizes on tonoplast. Yeast complementation verified that MoAE4 rescues boron sensitivity and endows NaHCO3 tolerance in the BOR1 deleted yeast. MoAE4 gene is bicarbonate induced in M. oryzae; and loss of MoAE4 (ΔMoAE4) resulted in mycelial growth inhibited by NaHCO3. Lucigenin fluorescence quenching assay confirmed that ΔMoAE4 accumulated less HCO3− in vacuole and more HCO3− in cytosol, revealing a real role of MoAE4 in bicarbonate transport. ΔMoAE4 was defective in conidiation, appressorium formation, and pathogenicity. More H2O2 was detected to be accumulated in ΔMoAE4 mycelia and infected rice cells. Summarily, our data delineate a cytomembrane and tonoplast located HCO3− transporter, which is required for development and pathogenicity in M. oryzae, and revealing a potential drug target for blast disease control.
Highlights
The bicarbonate anion (HCO3−)-transporter family, known as the SLC4 transporter family, functions to transport HCO3− across the plasma membrane and in the maintenance of intracellular pH value
The strains were cultured on PDA media to understand the effect on MoAE4 conidial production, and the conidia were cultured on oatmeal–tomato agar medium (OMA) media as previously described
Homologous sequences of anion exchange protein 4 (AE4) proteins have been reported in a variety of species
Summary
The bicarbonate anion (HCO3−)-transporter family, known as the SLC4 (solute carrier 4) transporter family, functions to transport HCO3− across the plasma membrane and in the maintenance of intracellular pH value. 39–50% identical to the electrogenic NBCs. the deduced amino acid sequences of HCO3− transporter proteins show a high degree of similarity to anion exchangers [2]. The well characterized anion exchanger 1 (AE1), the first bicarbonate transporter cloned and sequenced Cl−/HCO3− exchanger, is the erythrocyte band 3 glycoprotein that contains a membrane domain responsible for transport function. During invasive hyphae growth and development in the host plant, M. oryzae undergoes various harsher obstacles involving plant-derived passive and active resistance such as the accumulation of reactive oxygen species (ROS), antimicrobial compounds, and pathogenesis-related proteins for instance [21,22,23], and in planta nitrogen starvation, high- HCO3−, and low-oxygen stresses [24,25,26]. MoAE4 required for pathogenicity provides a new target for blast disease control
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