ABSTRACT

Drought and salinity are two major limiting factors in crop productivity. The drought–caused crop loss was over $1 billion annually in Texas, of which about half resulted from cotton loss. Besides drought, saline water and soils also contribute to the reduction in cotton yield and fiber quality in America’s Southwest. One way to reduce cotton loss caused by drought and salinity is to increase solute concentration in the vacuoles of cotton cells, so that the solute potential is more negative inside cells, resulting in water to move into cells and avoiding accumulation of sodium ion to toxic level in cytoplasm, therefore better water retention and higher salt tolerance can be achieved. The success of this approach was demonstrated in various plants by overexpressing the Arabidopsis genes AtNHX1 that encodes a sodium/proton antiporter and AVP1 that encodes a proton pump. Overexpression of AtNHX1 increases vacuolar uptake of sodium, whereas overexpression of AVP1 generates higher proton electrochemical gradient (PEG) across the vacuolar membrane that energizes secondary transporters including AtNHX1, both of which lead to increased vacuolar solute concentration and therefore higher salt- and drought-tolerance in transgenic plants. In an effort to engineer cotton for higher drought- and salt-tolerance, transgenic cotton plants that express AtNHX1 were created. Since AtNHX1 activity depends on PEG generated by proton pumps like AVP1, a coupled overexpression of AtNHX1 and AVP1 would potentially confer higher tolerance against drought and salt in transgenic plants. Therefore creating another transgenic cotton line that expresses the Arabidopsis AVP1 gene is also underway. It is hoped that AtNHX1- and AVP1-double overexpression cotton will be more drought- and salt-tolerant.