The Future of Drought Resistant Plants

Did you know that the global population will increase from 8 billion to 9.7 billion people by 2050? Did you also know that also by 2050, 95% of Earth's land will degrade? It may be impossible to continue mass producing food if current trends continue. Therefore, it is crucial to examine how plants respond to stressful conditions, such as drought and nutrient-poor soil. It is this problem that I have delved into in the Cell Signaling lab at the University of Texas.

Adenosine triphosphate [ATP]e, is most commonly known as a molecule that provides energy in the cells. However, ATP also exists outside of cells (extracellular ATP, or, eATP) and acts as a hormone. eATP binds to purinoceptors, which are receptors that specifically react with ATP. The binding then causes an increase in [Ca²⁺]_cyt (calcium). The calcium then plays a role in a cell signaling pathway in the cell that regulates how the rate of how quickly or slowly plants grow.

eATP triggered cell signaling pathways

Additionally, I looked at patellins. Patellins are a group of proteins that potentially play a critical role in eATP signaling pathways. Specifically, PATL4 overexpressors and patl2456 knockouts were examined. When a protein is overexpressed, it is produced in in greater amounts than normal. Inversely, a knockout is a technique where a specific gene (in this case, patellin proteins 2, 4, 5, and 6) is inactivated.

These overexpressors and knockouts were examined in order to test how certain patellin proteins interact with eATP and in eATP signaling pathways.

Stomata, treated to 2 mM ATP

In order to effectively track plant growth rates, we looked at root hairs and stomata. Root hairs grow relatively quickly and therefore can be tracked and measured easily. Stomata are pores on the underside of leaves and work to let in the necessary gases. These pores are sensitive to the environment, and close when the weather is too hot in order to conserve water. Stomata were measured by dividing their width by length.

Root hair

In figure 1, the relationship between patl2456 KO plants and 2 mM ATP was examined through measuring root hairs. It seems that the treatment of 2 mM ATP, when added to patl2456 KO plants, cause increased average root hair growth rates. Compared to the average root hair growth rate in WT (wild-type, or, normal) plants, the knockout plants saw greater growth. These suggest that in agricultural plants, such as cotton and soybean, introducing knockout plants and treating with a large dose of ATP would conclude in plants that produce more yield.

In figure 2, we again see exciting results! In PATL4 overexpressors, the addition of 10 uM ATPyS (read as ATP-gamma-s) causes significant root hair growth rates.

• For this experiment, ATPyS was utilized as a treatment due to ATP's tendency to be broken down quickly. To prevent this, especially because 10 uM is a small amount, the extra sulfur molecule is added to ATP.

These results signify that when patellin 4 protein is over-produced and treated with the 10 uM ATPyS, root hair growth rate could possibly be greater than in wild-type plants. This can potentially be transferred to agricultural plants.

In figure 3, we are able to examine the specific roles of patellin proteins 2, 4, 5, and 6 in plants. 10 uM ABA was added to both wild-type and patl2456 knockouts.

• ABA (Abscisic Acid) is a hormone in plants and is dubbed the drought hormone because it regulates plant responses to environmental stressors (so, especially drought)

These results are not very applicable, however. The added 200 uM ATPyS causes a decrease in stomatal aperture (opening of the stomata) compared to wild-type plants. But inconclusive or unfavorable results isn't always negative. Future researchers can then utilize a dose response curve and look at smaller or larger concentrations of ATPyS.

In figure 4, we examined the effects of the drought hormone ABA. Specifically, we looked at the effect of two concentrations on patl2456 knockouts: 10 uM and 20 uM. Though the difference in concentrations is minute, there are major differences in stomatal aperture in wild-type plants. This shows that low amounts of ABA curiously cause more stomatal closure than opening, which went against our hypothesis. In the knockout plants, however, 20 uM ABA had similar effects on stomata compared to 10 uM ABA. This gives us insight into the relationship between ABA and plants lacking the four patellin proteins. In the future, when curating drought resistant plants, the information that patl2456 knockouts are more sensitive to ABA will help researchers decide whether PATL4 overexpressors or patl2456 knockouts are better.

In conclusion, patellin knockouts and overexpressors could be potentially utilized to create drought-resistant agricultural plants. As nutrient-rich land degrades, it is crucial to come up with a solution before it is too late.