FY2011 Annual Report Project Descriptions

LIFE SCIENCES

5a

National Science Foundation
Characterization of a LATD-dependent ABA Signaling Pathway in Medicago truncatula roots.

Principal Investigator: J. Harris

Accomplishments & Outputs:
The purpose of this project is to determine the role of the LATD protein in the response of growing meristematic (stem cell) regions of the root system to the plant hormone, Abscisic Acid (ABA). Is there a legume-specific role, or do LATD, and proteins like it, perform similar functions in the root systems of non-legumes? During the past year we have determined that the LATD protein is required for normal cell elongation in the root. Since cell elongation is responsible for most of the rapid growth in roots, this alteration in latd mutants has a significant effect on root elongation. We have also determined that this process involves signaling by reactive oxygen species. Currently, we are examining ABA localization in growing roots to see how ABA transport can affect root development.

Outcomes & Impacts:
We have identified a set of transcription factors that are controlled by the LATD protein. We are currently designing experiments to determine how a subset of these transcription factors regulate root growth in response to the LATD protein. We have also determined that the LATD protein regulates levels of reactive oxygen species, in conjunction with the hormone Abscisic acid, to control cell elongation in the root tip. Identifying the function of the LATD protein would help us to understand how root growth and the development of nitrogen-fixing nodules are regulated by plant hormones. This research might ultimately lead to the development of non-legume crop species that nodulate, or better control of legume root architecture. This could benefit farmers, consumers and the country, by reducing our dependency on fossil fuels by reducing the industrial synthesis of fertilizer, and by increasing the productivity of crop plants.


5a

Hatch
A nodule regulatory network involving light, ethylene and jasmonic acid .

Principal Investigator: J. Harris

Accomplishments & Outputs:
The purpose of this project is to determine the mechanism by which Red and Far red light regulate the formation of nitrogen-fixing nodules in the model legume, Medicago truncatula. Far Red light is the light that plants see a lot of when they are shaded by other plants. Thus, testing the response of plants to Far Red light is very similar to testing the effect of plant crowding. We will specifically test the hypothesis that Red/Far Red light regulate nodulation by altering production or response to the gaseous hormone, ethylene. We examined whether the giraffe mutant plants that we found have altered response to Far Red light, both for nodulation and for other aspects of plant growth (such as shoot elongation and flowering time). We have found that giraffe plants are insensitive to Far Red light for inhibition of nodulation, indicating that the wild-type function of the GIRAFFE gene is required for the Far Red light response. We also found that providing giraffe plants with more ethylene (by adding the precursor molecule, ACC) can reduce nodule number, showing that giraffe plants can respond normally to ethylene. We did grafting experiments that determined that the GIRAFFE gene is required in the shoot, where much of the light is perceived, rather than in the root, where nodulation occurs. We have also tested another, more distantly related legume, Lotus japonicus, and found that Far Red light regulates nodulation in this plant species in the same way as it does in wild-type Medicago. This year, we examined the effect of different wavelengths of light on the expression of hormone biosynthetic enzymes and on hormone-responsive genes.

Outcomes & Impacts:
We have found that this effect of Far Red light on nodulation occurs in at least two different legume species. Our data so far are consistent with Red light stimulating nodulation and Far Red light inhibiting nodulation by inducing production or response to the stress hormone, ethylene. Interestingly, we have also found that Red light functions by inhibiting enzymes that synthesize another hormone, abscisic acid, and stimulating enzymes that promote its destruction. Since Far Red light is what plants see when they are shaded by other plants, this effect is significant and could have an impact on our agricultural practices. Thus the results of this work investigating the role of light signaling on nodulation could have a direct impact on farmers, particularly those involved in more sustainable agricultural practices involving legumes and inoculants. Red and Far Red light are used by plants to sense shading and proximity to neighboring plants. Thus, our data may result in recommendations that increased attention be paid to plant spacing to regulate irradiation of neighboring plants by far red light when increased nodulation is desired.


5a

Hatch
Fungal Biofilms and Development of New Anti-Fungal Drugs .

Principal Investigator: D. Johnson

Accomplishments & Outputs:
The purpose of this project is to understand the effects of small molecule inhibitors on yeast biofilm formation. These molecules inhibit the ability of yeast cells to change shape in response to environmental signals. 3 of the 21 molecules that we have studied also have the ability to inhibit biofilm formation, which is a major virulence determinant for the pathogenic yeast Candida albicans. We also determined that clinical isolates of C. albicans do not always behave as do laboratory strains, which has important ramifications for antifungal treatments. We have published two research manuscripts in the last year in the Journal of Medical Microbiology and in PLoS ONE. We will continue this research in the coming year, focusing on one specific molecule, ETYA, and its mode of action.

Outcomes & Impacts:
The major findings and conclusions are that several small molecules that inhibit yeast morphologies also inhibit biofilm formation, which is a major virulence determinant for the pathogenic yeast Candida albicans. In addition, we showed that clinical isolates of C. albicans do not always behave as do laboratory strains, which has important ramifications for antifungal treatments. The long-term benefit will be in the identification of new anti-fungal drugs, which are desperately needed by the immunocompromised patient population.

Publications:
Midkiff, J., N. Borochoff-Porte, D. White, and D.I. Johnson. 2011. Small molecule inhibitors of the Candida albicans budded-to-hyphal transition act through multiple signaling pathways. PLoS ONE 6:e25395.

Grald, A., P. Yargosz, S. Case, K. Shea, and D.I. Johnson. 2011. Small molecule inhibitors of biofilm formation in laboratory and clinical isolates of Candida albicans. J. Med. Microbiol, in press.


5c

Hatch
Roles of ER-alpha and ER-beta in Mammary Gland Cell Proliferation .

Principal Investigator: Z. Pan

Accomplishments & Outputs:
This project is to determine the function and underlying mechanism of ERa and ERb in mammary cell proliferation. ERa and ERb are the two types of estrogen receptors that mediate cellular response to estrogen stimulation. Estrogen is produced by the ovary and plays pivotal role in mammary cell proliferation. Optimal mammary cell proliferation is related to milk yield during lactation, while deregulated proliferation leads to breast cancer. In the past year, we used ER-selective agonists to activate ERa and ERb separately and determined the relative roles of ERa and ERb in mammary cell proliferation. We found that activation of ERa but not ERb leads to increased cell proliferation. While ERb activation did not affect much of mammary cell proliferation, co-activation of ERb and ERa lead to inhibition of ERa activity and ERa-promoted cell proliferation. These results support that ERa and ERb function antagonistic to each other and thus may form a balance in regulating mammary cell proliferation. The manuscript on these findings has been submitted for publication.

Outcomes & Impacts:
This study provides the first in vivo evidence that ERb can suppress the activity of ERa. The findings in this study shed lights on how to develop better hormone replacement therapy regimens with less risk for breast cancer.