Member SpotlightsDeveloping maize seed resistance to aflatoxigenic fungi Robert Brown, Ph.D.  Robert Brown Principal Investigator US Department of Agriculture Robert.Brown@ARS.USDA.GOV Educational and Professional background: I received a Bachelors degree in Biology with a minor in Chemistry from Iowa Wesleyan College. The majority of my Biology courses were Plant-Science oriented. I was awarded graduate teaching assistantships to pursue masters and Ph.D. studies. My Masters studies were completed at University of Wyoming in Botany with a research emphasis in fungal taxonomy. My interests in Mycology led me to pursue a Ph.D. in Plant Pathology, which I earned at Rutgers University. My research during masters and doctoral studies involved an approach which utilized morphological and protein profiling of fungi. I love working with fungi and also with proteins. While completing graduate studies I taught Science and Biology on a junior high and a high school level and I also taught Algebra at Seton Hall University. I also involved in teaching a summer course on Scientific Methodology to incoming freshman at Rutgers University as well as a required freshman course, Perspectives in Agriculture and the Environment. Prior to completing a Ph.D., I worked as a County Agricultural Agent for Rutgers Cooperative Extension Service with the responsibility of administering an urban vegetable gardening program. A few years after I earned a Ph.D., I took a position as a postdoctoral research associate with USDA-ARS in New Orleans and after 4 years in this position, was hired permanently as a research plant pathologist by the same research unit, Food and Feed Safety Research. I have been in New Orleans a total of 20 years. Awards or Distinctions I was elected to Sigma Xi, received the Secretary's (Secretary of Agriculture) Group Honor Award for research, was named Outstanding Professional Employee by the Federal Executive Board of New Orleans. I've been appointed to graduate faculties of Louisiana State University and Southern Illinois University and to Editorial Boards of 8 peer review journals. I am listed in several Who's Who biographical citations and I've been awarded several competitive research grants including the Foreign Agricultural Service, NRI and USAID. I've also received numerous cash awards for research achievements as an ARS scientist in New Orleans. I've been invited to speak at numerous national and international conferences including Gordon Conference on Mycotoxins; invited contributor of numerous book chapters and reviews. I am a Member of American Phytopathological Society, International Association of Plant Protection Sciences, American Association for the Advancement of Science, Association for International Agriculture and Rural Development, Maize Genetics Cooperation and the Proteome Society. Primary Scientific Interests and/or Expertise? My current interests are 1) developing knowledge pertaining to gene involvement in maize seed resistance to aflatoxigenic fungi and gaining an understanding of the regulation of such resistance; 2) use that knowledge to enhance resistance in commercial corn production. I am principal investigator on a project aimed at enhancing maize host resistance to aflatoxin contamination. This is a worldwide problem, and one serious enough to warrant FDA regulation of toxin levels in major commodities such as maize, cottonseed, peanuts, and tree nuts. What motivated you to pursue this research? A love of fungi especially from a physiological perspective, and a fascination with maize as a crop has contributed towards my research direction. Also, early on, I developed an assay that facilitated the screening of kernels (kernel screening assay or KSA) for aflatoxin accumulation in the lab as opposed to the field. The KSA has been used recently to assist a maize breeder in the development and release of new maize inbred lines with aflatoxin-resistance. The KSA also facilitated the development of a maize- A. flavus pathosystem for investigation that has advanced our understanding of kernel resistance. This has led to observations of changes in proteins in relation to kernel physiological changes and to infection (my old friends, fungi and proteins!), which has evolved into full-blown comparative investigations of gene expression and proteome analysis of maize lines varying in resistance to A. flavus. The work just seems to get more and more exciting! Your current research focuses on corn lines resistant to aflatoxin contamination by Aspergillus flavus. Give us some background on this fungus. Aspergillus flavus is a ubiquitous saprophyte yet opportunistic pathogen that infects plant tissue weakened by abiotic stress or insect injury. It produces aflatoxin as a secondary metabolite; aflatoxin is a very potent carcinogen. A. flavus continues to grow at high temperatures, ones that are restrictive to many competing soil fungi and it also grows under drier conditions than many fungi. Aflatoxin contamination is greatly enhanced by drought and high night-time temperatures. How do corn strains become contaminated with this toxin (what are its sources)? The fungus is present in the soil and only needs assistance with entry. A. flavus infects corn kernels during preharvest, either through kernel cracks and wounds or possibly silks. It is transported to the entry site by wind or insect. However, aflatoxin levels don’t increase until kernel maturity and during dry-down. Kernels can also become associated with the fungus after harvest especially under improper storage conditions. Aflatoxin levels can certainly proliferate under these conditions regardless of when infection occurred. How does aflatoxin compare to other toxins that may affect humans? What are its effects on the body & how is it metabolized? High exposure to high levels of aflatoxin B1 from the diet over a period of time is an important risk factor for the development of liver cancer. The association between dietary exposure and human liver cancer has been strong. With other mycotoxins, the association between exposure and disease has not been as clear. Acute ingestion of aflatoxin-contaminated grain over a short period of time was responsible for the death of a number of Kenyans four or five years ago. How is aflatoxin detected in humans and the foods they eat? I am not involved to any degree with detection in humans. There are a number of FDA-approved protocols for detecting aflatoxins in susceptible crops, the most accurate being HPLC. A number of workers, myself included, also use commercially-available immunoassay kits. To what extent are aflatoxin levels monitored and regulated by the FDA? How does your research contribute to these efforts? There is an action level of 20 ppb for interstate commerce. Lots exceeding this are usually allowed to be used in state in feed lots up to a point. Grain elevators monitor all shipments leaving port, but for those arriving, do so only upon request. I am involved in a research project which uses hyperspectral imaging cameras to detect and quantify aflatoxin levels. The quantification approach is still under development but results, thus far, are promising. This approach would be superior to presently used methods because it is very quick, nondestructive and represents a great improvement in measurement accuracy. What methods do you employ to develop corn strains resistant to aflatoxin contamination? How are proteomics & functional genomics utilized? First we identified and field- and KSA-tested aflatoxin-resistant lines found in the U.S. These lines, while displaying decent resistance, were in poor agronomic backgrounds. I was sent lines from Central and West Africa selected for ear rot resistance to fungi including A. flavus. These were tested via KSA and some were determined to be potentially aflatoxin-resistant. This served as the basis for a grant-funded collaboration between USDA-ARS-SRRC (Southern Regional Research Center) in New Orleans and International Institute of Tropical Agriculture (IITA) in Ibadan, Nigeria, to develop inbred lines with improved aflatoxin-resistance and good agronomic traits. Several lines were chosen from the African and the U.S. groups and crossed in Nigeria to make 2 populations: an F1 population and a backcross population (backcrossed to the U.S. parent). This would provide backgrounds potentially favorable for maize growth in both the U.S. and Africa. Lines were grown in Nigeria, selected for good agronomic characteristics and foliar disease resistance and self-pollinated to produce the next generation; this continued until the S4 generation which were sent to New Orleans and tested for aflatoxin accumulation by the KSA. From this point on lines were selfed to the next generation, tested by the KSA and advanced and tested in the field in Nigeria until we had a number of inbred lines (all traits fixed) with good agronomic features, and low toxin accumulation. After final field test confirmation, we registered and released six inbred lines with aflatoxin-resistance (see publication #4). We have been able to identify near-isogenic inbred lines varying in aflatoxin accumulation, among breeding materials generated in Nigeria. These have been used to conduct comparative proteomics studies to identify resistance-associated proteins (RAPs) and their corresponding genes. We've also performed characterization studies to determine protein/gene function (including RNAi gene silencing studies). This has enhanced our understanding of gene involvement in resistance and facilitated a search for markers which could be used to assist breeders in transferring resistance from new inbred lines to commercial backgrounds. This is not an easy task since aflatoxin-resistance is multi-gene controlled. We've also initiated microarray studies to investigate gene expression and identify factor(s) involved in gene regulation. Can you rate your progress thus far on the development of resistant strains; what are your failures & successes? I have had very good progress in that we've released 6 lines and have others being tested for future releases. What information is available to the public on this topic? I've listed 2 publications; the second describes the collaborative project between IITA in Nigeria and my lab in New Orleans. On the website I listed, there are other publications named as well. Is there anything else you'd like to contribute on your specific research or information on aflatoxin resistance development. Our investigations over the years have helped us compile a great deal of knowledge, not only about aflatoxin-resistance, but also about horizontal versus vertical resistance, the role in seed resistance of constitutive versus induced protein production, multifunctional aspects of proteins/genes, and the potential for agricultural crops to benefit human health and medicine. I believe that at least some of this knowledge will benefit science and society in ways far beyond the aflatoxin problem. Looking back, is your current career path what you expected it would be? I don't know that I had definite expectations regarding my career path other than to pursue research. However, I am very pleased with the fact that my research represents a progression on themes around which I've always been curious and found exciting. What are your career goals; what would you like to achieve with your research in the future? I'd like to make significant contributions to the development of controls for the aflatoxin problem through host resistance. Additionally, I would like to understand the roles of multifunctional proteins in plant life and development; (e.g. a number of proteins identified through research are antifungal, involved in stress tolerance and appear to have other functions as well). I'd also like to understand at molecular and metabolic levels, plant responses to biotic and abiotic stress. On the lighter side, what are your other hobbies, interests, activities? I love following sports; favorites are football, basketball and lacrosse. You can learn more about Dr. Brown through his website http://www.ars.usda.gov/pandp/people/people.htm?personid=685 . Please also find some of his recent publications below. 1. Chen, Z.-Y., Brown, R. L., Rajasekaran, K., Damann, K. E. and Cleveland, T. E. Identification of a maize kernel pathogenesis-related protein and evidence for its involvement in resistance to Aspergillus flavus infection and aflatoxin production. Phytopathology. 96(1):87-95. 2006. 2. Brown, R. L., Chen, Z.-Y., Menkir, A. and Cleveland, T. E. Proteomics to identify resistance factors in corn. Mycotoxin Res. 22:(1) 22-26. 2006. 3. Menkir, A., Brown, R. L., Bandyopadhyay, R.., Chen, Z.-Y. and Cleveland, T. E. A U.S.A.-Africa collaborative strategy for identifying, characterizing, and developing maize germplasm with resistance to aflatoxin contamination. Mycopathologia. 162:225-232. 2006. 4. Menkir, A., Brown, R.L., Bandyopadhyay, R. and Cleveland, T.E. Registration of six tropical maize germplasm lines with resistance to aflatoxin contamination. Journal of Plant Registrations 2:246-250. 2008. 5. Yao, H., Hruska, Z., Kincaid, R., Brown, R.L., and Cleveland, T.E. Differentiation of toxigenic fungi using hyperspectral imagery. Sensing and Instrumentation for Food Quality and Safety 2:215-224. 2008. 6. Baker, R., Brown, R.L., Cleveland, T.E., Chen, Z.-Y., and Fakhoury, A. COR, a maize lectin-like protein with antifungal activity against Aspergillus flavus. J. Food Prot. 72:120-127. 2009. ### << Previous Next >> [ View All Member Spotlights ] |
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