Both natural and human-induced activities have led to contamination of soil and water in the environment. Environmental pollutants can be associated with increased health risks and a decrease in arable land and drinking water. Cleaning polluted lands is of great concern, but is often viewed as an economic burden.

Phytoremediation is the use of plants to naturally clean and remediate polluted soil and groundwater, and can be less of an economic strain compared to conventional engineering approaches. Most of my phytoremediation-realted research has focused on understanding pathways that lead to increased plant tolerance of selenium, which at high levels is a public health concern in the Rocky Mountain region.

There are currently two projects underway that are relavent to phytoremediation. The first involves investigating if the gene APR2 has an effect in selenium tolerance in the model plant Arabidopsis. The APR2 enzyme catalyzes the reaction of sulfate to sulfite, and is one of the rate-limiting steps in essential sulfur assimilation in plants. My hypothesis is that APR2 similarly converts selenate to selenite, and is involved in Se tolerance and metabolism in plants. The project includes both reducing and increasing the expression of the APR2 protein using molecular techniques. This project is funded by the NSF (2010-2013).

The second project examines the ability of blackneedle rush, a dominant plant in marsh and estuaries ecosystems in southeastern USA, to accumulate excessive amounts of zinc in their tissue. XRF and XANES analyses at the ALS synchotron in Berkeley, CA, suggest that zinc accumulates on the root surface as an inorganic form of hydrated zinc-phoshphate (zinc-hopeite and zinc-hydroxyapatite). Further characterization of these plants is underway, and may reveal insight into the physiology of these plants.

Above: XRF mapping of iron (red) and zinc (green) in roots of blackneedle rush.
XRD and XANES analysis both inducates that zinc accumulates as inorganic
zinc-phosphate in clustered "hot spots" on the surface of the root.

Selenium is thought to be toxic to plants because it can be assimiliated into selenocysteine. This is problematic, as selenocysteine can replace the amino acid cysteine in proteins, potentialy causing proteins to misfold. On a cellular level, ubiquitin binds to misfolded proteins, which targets the misfolded proteins to the proteasome where they are eventually destroyed. Therefore, the proteasome prevents cellular stress by preventing the formation of misfolded protein aggregates.

Two questions drive this research project: Are selenium-containing proteins directed to the proteasome for degradation? Do plants that hyperaccumulate and tolerate selenium have an enhanced capacity to direct and degrade seleno-protesins via the proteasome?

The use of biofuels as an alternative source of energy has the potential to decrease foreign dependence on fossil fuels and perhaps reduce anthropogenic sources of global warming. The largest class of biofuels is ethanol. Ethanol production from corn is met with skepticism, as it competes with food production and is likely to be ecologically unsustainable. Currently, ethanol is derived from the sugars found exclusively in corn kernels. It would be much more desirable if ethanol could be produced from cellulose, which is the primary sugar found throughout all plants. However, cellulose is much more resistant to fermentation, and major hurdles need to be overcome before cellulose-derived ethanol is realized.

Despite cellulose's recalcitrance, certain bacteria and fungi posses enzymes called cellulases, which can degrade plant cellulose into simple sugars. For example, Trichoderma reesei is a soil fungus and is perhaps the best known microbe that utilizes cellulases. Industry has safely used T. reesei for years to optimize cellulose degradation. However, this process is extremely expensive and has limitations.

The genome of T. reesei has recently been sequenced, and the cellulases of this organism has been identified. I have obtained cDNA of T. reesei grown on cellulose, and would like express a few of the cellulases in the model plant Arabidopsis.

Signficance of research: Expression of a fungal cellulase in plants may accelerate the breakdown on celluloase in plants, which will make fermentation of the entire plant more feasilbe to ultimately create biofules. However, it is also likley there will be no effect as other enzymes are needed. Still, it is possible that vast amounts of cellulase will be produced harmlessly in plants, which can be then be safely purified in order to augment industrial fermentation.