Research Areas:
        My research program is focused on achieving two major objectives: increasing our understanding of the molecular signaling pathways that lead to the activation of defense pathways in plants, and applying this knowledge to improve disease resistance in cereal crops. Our work is carried out in collaboration with the other researchers of the USDA-ARS Crop Production and Pest Control Unit and the Small Grains Research Group, at Purdue, that study a range of agriculturally significant fungal, viral and insect diseases of cereals. 

       To achieve the first goal, my group has developed a high-throughput virus-induced gene silencing (VIGS) system to identify genes encoding functions required for disease resistance.   We will then begin to investigate how the gene products function in the mechanisms of resistance, and determine if they may be useful in achieving the second objective.  Our VIGS system is based on barley stripe mosaic virus (BSMV) and has proven very useful in the analysis of disease resistance pathways in hexaploid wheat.  Our work employing this system to identify genes required for leaf rust resistance in wheat was recently published (Scofield et. al., 2005).

Silencing phytoene desaturase in the leaves of hexaploid wheat by BSMV-VIGS.
The first and second leaves of wheat cultivar Bobwhite were inoculated with BSMV:00 and BSMV:PDS and photographed 14
 

Leaf rust interactions of susceptible and resistant wheat after infection with control BSMV-VIGS  constructs or  constructs designed to silence genes encoding components of the Lr21-mediated resistance pathway.  All plants were infected with the indicated BSMV constructs 7 days after germination and then spray inoculated with the avirulent P. triticina isolate PTRUS6 8 days after viral infection.  The photographs were taken 10 days after inoculation with leaf rust and are representative of all leaves in two different experiments.

Infection with control constructs does not alter resistance or susceptibility.  The infection types of the susceptible (S) cultivar Wichita  (1), and the resistant (R) line WGR7 (2) inoculated with BSMV:00. The necrotic spots in (2) are sites of Lr21-dependent HR.

Leaves 3-5 come from a separate experiment from those shown in 1 and 2.  Infection type of susceptible cultivar (S) inoculated with BSMV:00 (3) is shown on the left as a control.  Infection with BSMV:PDS4as does not alter the infection type of the susceptible line (4) or the resistant cultivar (5).

The effects of silencing Lr21, RAR1, SGT1 and HSP90 on Lr21-mediated resistance.  Ten plants resistant to PTRUS6 were inoculated with (1) BSMV:00, (2) BSMV:Lr21, (3) BSMV:RAR1, (4) BSMV:SGT1 and (5) BSMV:HSP90, 7 days after germination and sprayed with PTRUS6 8 day later. 

     Our approach to the second goal is to harness the power of naturally occurring disease resistance pathways, which are able to provide highly effective resistance to specific pathogens.  These resistance systems have been used for decades to provide protection against particular “target” pathogens. Unfortunately, there are many significant pathogens for which no corresponding plant resistance systems are known.  However, my recent work in industry, and the findings of others, demonstrate that some resistance pathways can, in fact, provide resistance to a broad-spectrum of “non-target” pathogens when they are engineered to be activated when the plant is attacked by “non-target” pathogens. To this end, we are using the tools of genetic engineering to test existing resistance pathways for the ability to provide defense against agriculturally important “non-target” pathogens, and developing strategies so that these pathways can be appropriated activated by these “non-target” pathogens.

Professional Experience:

2002-Present  Research Geneticist, USDA-ARS and Adjunct Assistant Professor, Department of Agronomy, Purdue University

1997-2002  Pathogenomics Group Leader, DNA Plant Technology Corporation, Oakland, CA.

1997-1992  Assistant Research Geneticist,  NSF Center for Engineering Plants for Resistance  to Pathogens, University of California-Davis.

1988-1992  Post-doctoral Fellow, Sainsbury Laboratory, John Innes Centre, Norwich, UK  Advisor; Jonathan Jones.

1985-1988  Post-doctoral Fellow, Plant Breeding Institute, Cambridge, UK.  Advisor:  Mike Bevan.

Most Significant Publications:

Sindhu, A., Chintamanani, S., Brandt, A.S., Zanis, M., Scofield, S.R., and Johal, G.S.  (2008) A guardian of grasses: specific origin and conservation of a unique disease resistance gene in the grass lineage.  Proc. Natl. Acad. Sci. USA 105: 1762-1767.    Earth and Sky Radio Website

Scofield, S.R., Huang, L. Brandt, AS and Gill, BS Development of a virus-induced gene silencing system for hexaploid wheat and its use in functional analysis of the Lr21-mediated leaf rust resistance pathway.  Plant Physiol. 138: 2165-2173, 2005.  

Scofield, S.R., Tobias, C., Rathjen, J.R., Chang, J.A., Lavelle, D.T., Michelmore, R.W. and Staskawicz, B.J.  (1996)  The molecular basis of gene-for-gene specificity in bacterial speck disease of tomato.  Science 274: 2063-2065.

Salmeron, J.M., Oldroyd, G.E.D., Rommens, C.M.T., Scofield, S.R., Kim, H.S., Lavelle, D.T., Dahlbeck, D. and Staskawicz, B.J. (1996).  Tomato Prf is a member of the leucine-rich repeat class of plant disease resistance genes and lies embedded within the Pto kinase gene cluster. Cell 86: 123-133.

Scofield, S.R., English J.J., and Jones, J.D.G.  (1993)  High level expression of the Activator Transposase gene inhibits the excision of dissociation in tobacco cotyledons.  Cell 75: 507-517. 

Education:
A.B. Political Science, Kenyon College, Gambier, OH 1976
Ph.D. Molecular Genetics, Indiana University, 1985

Date joined staff:  2002

Last updated:  April, 2008