Co-overexpression of AVP1 and AtNHX1 in Cotton Further Improves Drought and Salt Tolerance in Transgenic Cotton Plants

Salinity and drought are two major environmental stresses that limit the growth and productivity of cotton. To improve cotton's drought and salt tolerance, transgenic cotton plants expressing the Arabidopsis vacuolar Na+/H+ antiporter gene AtNHX1 and H+-pyrophosphatase gene AVP1 were produced by cross-pollination of two single-gene-overexpressing plants. The salt tolerance and drought tolerance were further enhanced by simultaneously overexpressing AVP1 and AtNHX1 in comparison to AVP1 or AtNHX1 single-gene-overexpressing plants and to wild-type plants. Plant height, boll number, and fiber yield of AVP1/AtNHX1-co-overexpressing plants were higher than those of AVP1-overexpressing, AtNHX1-overexpressing, segregated non-transgenic line, and wild-type plants under saline and drought conditions. The photosynthetic rate of AVP1/AtNHX1-co-overexpressing plants was significantly higher than that of single-gene-overexpressing and wild-type plants under 200 mM NaCl treatment. In addition, the root systems of AVP1/AtNHX1-co-overexpressing plants were larger than those of single-gene-overexpressing and wild-type plants, which was likely due to increased auxin polar transport in the root systems of the AVP1/AtNHX1-co-overexpressing plants. Moreover, these AVP1/AtNHX1-co-overexpressing cotton plants produced 24 % higher fiber yield under low-irrigation conditions and 35 % higher fiber yield under dryland conditions as compared to wild-type cotton in the field.