Potassium is the most abundant inorganic solute in plant cells and is
involved in plant responses to abiotic and biotic stresses. Previous studies
have shown that altering the level of potassium can reduce the spread of
viral diseases. Thus, potassium transporters are leading targets for
breeding for virus resistance, including soybean mosaic virus (SMV), the
most prevalent viral disease in soybean.

Addition of potassium fertilizer was found to significantly reduce SMV
incidence. Upon analysis, the gene GmAKT2 was significantly induced by SMV
inoculation in resistant varieties but not in susceptible varieties.
Transgenic soybean overexpressing GmAKT2 were also generated and evaluated.
Significant increase in potassium concentrations was observed in young
leaves of the transgenic soybean. Meanwhile, potassium concentrations in the
old leaves of the transgenic plants were lower than in wildtype plants.
These indicate that GmAKT2 acted as a potassium transporter and affected the
distribution of potassium in soybean plants.

Wildtype plants exhibited severe mosaic symptoms while transgenic plants
showed no symptoms of SMV, suggesting that virus development was
significantly retarded in the transgenic soybean plants. Overexpression of
GmAKT2 enhanced SMV resistance in soybean. Hence, manipulation of potassium
transporter expression is a novel molecular approach for enhancing SMV
resistance.

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