Submitted to: Plant Signaling and Behavior
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2011
Publication Date: 6/6/2011
Citation: Zhang, H., Shen, G., Kuppu, S., Gaxiola, R., Payton, P.R. 2011. Creating Drought- and Salt-Tolerant Crops by Overexpressing a Vacuolar Pyrophosphatase Gene. Plant Signaling and Behavior. 10.4161/psb.6.6.15223. Interpretive Summary: Drought and salinity are major environmental factors that limit agricultural production in most parts of the world. The projected increase in world population growth, 9 billion people by the year 2050, suggests that food production and food security will be the primary concerns driving global politics and social dynamics. One constraining factor facing us is that the increased production of food will have to be achieved on more marginal land and with less water. Our laboratories have initiated studies investigating the molecular mechanisms controlling drought and salt stress with the goal of genetically engineering tolerance to these stresses. We previously reported that over-expression of a gene that pumps sodium ions into the vacuole results in tolerance to salt stress. We concluded that this increased capacity for ion sequestration in the vacuole prevented toxic levels of salt ions from accumulating in the cytosol. Interestingly, constitutive over-expression of this gene also had a positive effect on root growth and resulted in increased drought tolerance. The effect on root growth had been observed in previous studies by Roberto Gaxiola and his lab recently reported data suggesting that over-expression of AVP1 had an effect on polar auxin transport. Auxin is a major plant hormone that plays a role in many plant developmental processes, including root growth. This manuscript is an addendum to previously published work on cotton plants that over-express the AVP1 gene. Here we present our findings on the effect of over-expression of AVP1 and its effect on auxin transport and lateral root growth. We observed over-expression of AVP1 counteracts the effects of naphthylphthalamic acid (NPA), a strong inhibitor of auxin transport. NPA treatment via agarose gel growth medium completely inhibits lateral root growth in wild-type plants and while root growth is inhibited in transgenic plants, the effect is significantly less so. Given this information and our previously published observations of drought and salt tolerance under both glasshouse and field studies, we believe that AVP1 is a viable candidate for commercialization of genetically engineered, stress-tolerant crops. Further research into root growth dynamics under field conditions for both salt and drought treatments are planned.
Technical Abstract: Increased expression of an Arabidopsis vacuolar pyrophosphatase gene, AVP1, leads to increased drought and salt tolerance in transgenic plants, which has been demonstrated in laboratory and field conditions. The molecular mechanism of AVP1-mediated drought resistance is likely due to increased proton pump activity of the vacuolar pyrophosphatase, which generates a higher proton electrochemical gradient across the vacuolar membrane, leading to lower water potential in the plant vacuole and higher secondary transporter activities that prevent ion accumulation to toxic levels in the cytoplasm. Additionally, overexpression of AVP1 appears to stimulate auxin polar transport, which in turn stimulates root development. The larger root system allows AVP1-overexpressing plants to absorb water more efficiently under drought and saline conditions, resulting in stress tolerance and increased yields. Multi-year field-trial data indicate that overexpression of AVP1 in cotton leads to at least 20% more fiber yield than wild-type control plants in dryland conditions and highlights the potential use of AVP1 in improving drought tolerance in crops in arid and semiarid areas of the world.