From Left to Right: Kristin K. Wobbe, Shereen Elkholy, and Pamela K. Weathers.

Artemisinin: The Biosynthetic Pathway and Its Regulation in Artemisia Annua, a Terpenoid-Rich Species

Artemisinin, a sesquiterpene lactone isolated from the aerial parts of Artemisia anuua L. plants, is currently the best therapeutic against both drug-resistant and cerebral malaria-causing strains of Plasmodium falciparum. It has also been shown to be effective against other diseases including schistosomiasis and hepatitis as well as many types of tumors. Although chemical synthesis of artemisinin is possible, it is not economically feasible. The relatively low yield (0.01-0.8%) of artemisinin in A. annua further limits commercialization of the drug. Therefore, the enhanced production of artemisinin in cell/tissue culture or in whole plants of A. annua is highly desirable. Although most genes of the artemisinin biosynthetic pathway have now been identified, little is known about their regulation in the plant. This critical review covers recent developments related to the biosynthesis and regulation of this important compound and related terpenoids and the production of these compounds in both microbes, and in whole plants and cultured tissues. Pamela J. Weathers, Shereen Elkholy, and Kristin K. Wobbe. Artemisinin: the Biosynthetic Pathway and Its Regulation in Artemisia annua, a Terpenoid-rich Species, In Vitro Cellular & Developmental Biology - Plant, 42:309-317, 2006.

HFrom Left to Right: Heidi F. Kaeppler, Alvar Carlson, and Ronald Skadsen.

Barley Hordothionin Accumulates in Transgenic Oat Seeds and Purified Protein Retains Antifungal Properties In Vitro

Pathogen attack of agricultural crops leads to significant losses in yield and quality both locally and globally. The tremendous impact of these losses has prompted widespread investigation of various means of genetically enhancing host plant resistance to disease. Examples of current transgenic approaches toward improved pathogen resistance in plants include overexpression of resistance cascade regulatory genes, silencing of endogenous pathogen gene expression, and overexpression of genes encoding antibiotic/antifungal compounds. As part of a larger research program investigating effects of several different types of transgenes on resistance to fungal pathogens in cereal crops (oat, wheat, maize and barley), we overexpressed a type-1 barley hordothionin gene (Hth1) in oat to test its function as an antifungal gene in a heterologous cereal species. Thionins are small, pathogenesis-related (PR) proteins produced by plants in response to pathogen attack. They have previously been shown to act as antifungal compounds through permeabilization and rupture of fungal hyphal membranes. Overexpression of Hth1 in oat led to accumulation of barley hordothionin in seeds of the transgenic lines. We isolated and quantified the protein, tested it in replicated in vitro assays, and were able to show that barley hordothionin was produced in biologically significant concentrations in oat and that its anti-fungal properties were maintained. Growth of the devastating cereal crop pathogen, Fusarium graminearum, was reduced in vitro due to barely hordothionin, providing support for further study of hordothionin overexpression as a means to enhance resistance to F.graminearum in cereals. Future studies investigating effects of high-level expression of hordothionin protein in specific tissues invaded by Fusarium (and other fungal pathogens) during the infection process would be beneficial in gauging the utility of this approach for satisfactory control of fungal diseases in cereal crops. Alvar Carlson, Ronald Skadsen, and Heidi F. Kaeppler. Barley Hordothionin Accumulates in Transgenic Oat Seeds and Purified Protein Retains Antifungal Properties In Vitro, In Vitro Cellular & Developmental Biology-Plant, 42:318-323, 2006.

From Left to Right: Michael Kane, Phil Kauth, Carmen Valero Aracama, Scott Stewart, Daniela Dutra, and Nancy Philman.

Photosynthetic and Carbohydrate Status of Easy- and Difficult-to-acclimatize Sea Oats (Uniola Paniculata L.) Genotypes During In Vitro Culture and Ex Vitro Acclimatization

The coastal dune systems along the southeastern United States serve as a natural defense system against erosion and economic damage following from hurricanes and tropical storms. In the southeastern United States, seed propagated sea oats (Uniola paniculata L.), a native perennial dune grass, is the dominant species planted. Nursery-grown sea oats, propagated from field-harvested seed have proven to be the most reliable source for transplants but hurricane induced damage to native seed producing stands has significantly limited the sources of sea oats seed. Nancy Philman, in Mike Kane's lab group had developed a micropropagation protocol to mass-produce sea oats. However, when the protocol was applied to produce multiple sea oats genotypes, significant differences in capacities for ex vitro acclimatization were observed. The ability to in vitro propagate diverse genotypes is required for protocol to be ecologically and commercially viable. In the laboratories of Drs. Mike Kane, Sandy Wilson and Joe Vu, Carmen Valero Aracama, then a doctoral student, studied the physiological/cultural basis for the low acclimatization capacity in some sea oats genotypes by comparing the photosynthetic capacity, carbohydrate status, and the activity of key photosynthetic enzymes between an easy- and very difficult-to-acclimatize sea oats genotype. Carmen determined that the primary distinction between these genotypes was a difference in photosynthetic capacity. The easy-to-acclimatize genotype produced leaves in vitro that were morphologically similar to ex-vitro produced leaves and exhibited similar photosynthetic competence as ex vitro produced leaves. Both ribulose 1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase activities in vitro were higher just prior to acclimatization. Carbohydrate analysis in vitro revealed that the easy to acclimatize genotype utilized leaf starch reserves more rapidly but this was offset by ex vitro net photosynthetic rates that were eight times greater than the difficult-to-acclimatize genotype. Subsequent research indicated that alterations in in vitro culture conditions and medium components, particularly cytokinins, had a profound effect on ex vitro acclimatization. Carmen Valero Aracama, Michael E. Kane, Sandra B. Wilson, Joseph C. Vu, Joan Anderson, and Nancy L. Philman. Photosynthetic and Carbohydrate Status of Easy- and Difficult-to-acclimatize Sea Oats (Uniola Paniculata L.) Genotypes During In Vitro Culture and Ex Vitro Acclimatization, In Vitro Cellular & Developmental Biology-Plant, 42:572-583, 2006.