Research Program

1. The main emphasis of my research program is geared toward unraveling stress tolerance mechanisms in plant species.

Drought stress mechanisms are studied using Citrullus colocynthis as a model species. This species is widely distributed in the Sahara-Arabian desert of Africa and the Mediterranean, and closely related the cultivated and domesticated watermelon (C. lanatus), an important cucurbit crop in Alabama. cDNA-AFLP and real-time RT-PCR were used to study differential gene expression in C. colocynthis seedlings under drought stress and several different hormone treatments. Results indicated that a complex interplay between ABA (abscisic acid), JA (jasmonic acid) and SA (salicylic acid) signaling pathways regulate plant gene expression in C. colocynthis during drought stress. Two genes, RBOHD (respiratory burst oxidase homolog D) and GRAS (GAI, RGA, and SCR) were selected for further characterization. These genes showed tissue specific expression and are known to encode proteins that are important factors in plant signaling pathways.

Cold stress tolerance mechanisms are investigated in Poncirus trifoliata and Satsuma mandarin(Citrus unshiu). This research was funded in part by USDA CSREES Special Research grants OEP 2001-03124 and 2002-06162 entitled "Technology and Market Development of the Gulf Coast Satsuma Mandarin Industry”. Low temperatures are a continuing threat to the commercial citrus industry in AL. P. trifoliata is a cold-hardy species used commercially as rootstock to impart cold tolerances to the citrus scion. mRNA differential display and cDNA-AFLP were used to study gene expression of P. trifoliata under a gradual cold-acclimation regime and during cold shock. Several up- and down-regulated fragments were isolated and sequenced. Up-regulated genes showed high similarity to genes involved in osmotic regulation, dehydration tolerance and scavenging of reactive oxygen species. Down regulated genes showed homology to genes involved in photo protection and the control of expression of genes related to photosynthesis. Similar studies will be carried out using Satsuma. The complex changes happening within plants during cold acclimation will require a thorough understanding of deficiencies in cold acclimation of freeze-sensitive species before they can be genetically transformed to impart greater cold tolerance.

2. The second area of interest is related to the investigation of the phylogeny and biogeography of Castanea species.

American Castanea species (the American chestnut and chinkapin) are susceptible to chestnut blight, a devastating fungal disease, which has reduced the species from major timber trees into minor under story shrubs. Funding has been made available by the USDA and conservation societies to evaluate the genetic diversity of the remaining American Castanea populations in order to design effective conservation strategies. Chinese Castanea species are known to have different levels of resistance and have been used extensively in breeding programs attempting to develop blight resistant American chestnuts. To infer the biogeographical history of the genus, the phylogeny of Castanea was estimated using five chloroplast (cp) DNA sequence data sets. The cpDNA patterns were found to be geographically structured. Higher levels of cpDNA diversity were found in Asia as compared to North America and Europe. It is hypothesized that Castanea originated in Eastern Asia (Japanese and Chinese chestnut and chinkapin) and dispersed from Asia to Europe (European chestnut) and onto North America (American chestnut and Allegheny and Ozark chinkapin). The Japanese chestnut was shown to represent an early divergence of the genus in Asia, while the Ozark chinkapin is an early divergence on the American continent. Different portions of the chloroplast genome evolved at different rates and can be used at different phylogenetic levels. CpDNA and single copy nuclear gene sequences will be used to study diversity, geographic variation in natural populations of the American Castanea species in the Appalachian ecosystem. SNPs are being developed for use in species specific DNA fingerprints.

3. Understanding the genetic information present within crops provides insights into plant evolution and new tools for crop improvement.

The domestication of watermelon resulted in significant changes in the morphology, physiology, genetic diversity and adaptation of the species. To gain a better understanding of evolutionary diversification of watermelon and its relationship to other species in the genus with higher levels of disease and drought resistance, the chloroplast genome was studied. Chloroplasts are abundant components of the plant cell and their genome is conservative in terms of size, structure and gene order and can be used in molecular systematics to trace geographic patterns. Chloroplast DNA from a diverse collection of watermelon forms and species has been investigated. Watermelon appears very closely related to Citrullus ecirrhosus, a drought resistant species from Namibia. Domestication routes from Egypt into several different directions were indicated for the bitter apple or C. colocynthis. Single copy nuclear sequence information will subsequently be used to better trace watermelon’s evolutionary patterns and geographical origins. It is anticipated that this will lead to a understanding of the key loci induced during domestication.

4. Another area of interest has been to use bioluminescence for the identification of phytopathogens and plant disease control agents in epidemiological studies.

The development of bioluminescent plant pathogens (genetically engineered with the luxCDABE genes) enabled the study of disease initiation and progress under varying environmental conditions . Bioluminescent Xanthomonas campestris pv. campestris (strain FD91L), causal agent of black rot of cabbage, has been used extensively to study microbial ecology and disease protection. Click here to see images of growth of bioluminescent Xcc in susceptible versus resistant cabbage Click here to see a list of References

Click here to see images of growth of bioluminescent Xcc in susceptible versus resistant cabbage

Click here to see a list of References