Research Interests

This laboratory’s focus is on the development and use of genetic engineering strategies for monocotyledonous species, such as wheat (Triticum aestivu), maize (Zea mays), oats Avena sativa), barley (Hordeum vulgare), rice (Oryza sativa) and grass species, like Festuca spp., Dactylis glomerata, and Poa pratensis. Our long-term objectives are to use transformed cereals and grasses to explore basic biological questions and to use this information to improve crops.

Although methods for stably transforming cereal and grass species are more routine today, several challenges occurred when using these technologies to improve crop species. Nearly all methods for cereal transformation utilize in vitro-derived tissue culture materials; this leads directly or indirectly to limits in the varieties that can be transformed, to somaclonal variation and to transgene expression instability.

Transformation routinely involves culturing of immature embryos to obtain embryogenic callus, which is often successful for model genotypes but not for commercial varieties. For this reason, we developed alternative methods of culturing, including new target tissues and new methods for gene delivery. This required a better understanding of the biological nature of target tissues and their in vitro response. This was accomplished by using probes to define the developmental state of the tissue at the molecular level (Zhang et al., 1998, 2002a).

Based on these efforts we developed efficient transformation methods for many previously recalcitrant varieties of wheat, barley, corn, rice, oat, sorghum and forage and turf grasses (e.g., (Cho et al., 1998, 1999a, Zhang et al., 1999, 2002b). The resultant transgenic plants were studied using cytogenetic analysis and methylation polymorphism to identify and ameliorate the underlying causes of somaclonal variation (with P. Bregitzer, USDA, Aberdeen ID; Bregitzer et al., 1998; 2002). Transgene expression instability was addressed using maize transposable elements as gene delivery vehicles – in barley transgenes delivered with this method had stabilized gene expression (Koprek et al., 2000, 2001).

The transformation methods were used to over-express in transgenic cereals the natural redox protein, thioredoxin, and its companion, NADP thioredoxin reductase (with B. Buchanan, UCB). To achieve maximal over-expression in the grain, we used seed-specific promoters and vacuolar targeting to direct the transgene to the endosperm (Cho et al., 1999b). Homozygous seeds were assessed for faster germination in barley (Cho et al., 1999), lower allergenicity (Kim et al., 2003, page 21) and better dough quality in wheat (unpublished) and hyperdigestibility in sorghum (unpublished), as was demonstrated by in vitro experiments with these cereals. The work on sorghum, which involves improving digestibility and amino acid quality, is a part of the Gates Grand Challenges for Global Health (http://www.supersorghum.org/). Experiments with the transgenic barley grains also revealed evidence that the starchy endosperm, once thought to be a “dead” tissue, can communicate with the embryo and the aleurone (Wong et al., 2002).

Another focus of the lab relates to functional genomics efforts in barley that provide information for other large genome cereals, like wheat. We introduced separately into barley the maize transposable element, Ds, and the transposase gene. When individual plants were crossed, Ds was activated and transposed to new locations in the genome with a preference to insert into genic regions – an advantageous trait for large genome species. Using the Ds sequence as a tag, the sequence can be used as a priming site to identify the gene into which Ds transposed and to map its location (Cooper et al., 2004; Singh et al., 2005; http://wheat.pw.usda.gov/BarleyTNP/). By identifying Ds elements that map close to phenotypes or genes of interest the element can be reactivated and Ds generally will transpose to nearby locations. One gene tagged by this approach is a wall-associated kinase gene or WAK, shown to be a 125-member family in rice (Zhang et al., 2005) that, based on studies in Arabidopsis, is involved in biotic and abiotic stress tolerance (with Z-H He, San Francisco State).

Outreach Interests

As a Cooperative Extension Specialist I have statewide responsibility for outreach and educational programming related to agriculture and foods. My outreach efforts are designed to increase public understanding of agricultural practices, food production and the impact of new technologies on food and agriculture. I am involved in the development of numerous educational programs and materials aimed at agricultural issues, including an award winning, informational website, http://ucbiotech.org/, intended to provide scientifically based information and resources to educators. I have also been involved in creating resources, like educational games, displays, videos and popular press articles. I have given a large number of lectures in local, state, national and international venues and served on a number of local, state and national committees relating to biotechnology and agriculture. Graduate students and postdoctoral fellows are invited to participate in these efforts.