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SESSION 1 - Discovery - New horizons in plant pathology - page 9 / 65





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(Gregersen and Collinge, J. Plant Pathol. 83:257-260, 2001). Of those that have been identified, we have chosen to concentrate on the NAC-domain protein family of transcription factors (Aida et al., Mutant. Plant Cell 9:841-857, 1997). The public barley EST data bases (URL) now contain approaching 400,000 barley cDNA sequences, many of which have been obtained from libraries prepared from plants infected with the powdery mildew fungus. Among these, s ome 300 cDNAs representing 14 different NAC-domain transcript families have been identified to date. We will present data illustrating post genomic approaches to determine the role of members of this family of plant-specific transcription factors in barley.

Role of Cell-cell signaling in virulence of Xanthomonas oryzae pv. oryzae

Chatterjee S1,2 and Sonti R.V2

1Centre for Biotechnology, School of Life Science, Visva-Bharati University, Santiniketan-731235, India, 2Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad – 500 007, India

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight, a serious disease of rice. Previously identified virulence factors of Xoo include an extracellular polysaccharide (EPS) as well as certain bacterial protein secretion systems and their effectors. Using molecular genetic approaches, we have characterized one novel virulence deficient mutant of Xoo that is EPS+ and proficient for protein secretion. This mutant is defective in a gene called rpfF (regulation of pathogenicity factor), which is involved in the synthesis of an extracellular diffusible factor (DSF) that promotes Xoo growth in rice leaves, by facilitating iron uptake. This is the first direct evidence that particular iron uptake systems are crucial for virulence of the important xanthomonad group of plant pathogens. In order to identify candidate genes regulated by the DSF, we undertook differential display and candidate gene approaches to identify downstream genes regulated by the Diffusible factor in Xoo.

Dothistroma needle blight of pines and the dothistromin toxin

R.E. Bradshaw, P.G.Long*, A. Schwelm, P. West

Institute of Molecular BioSciences and Institute of Natural resources*, Massey University, Private Bag 11222, Palmerston North, New Zealand

Dothistroma (red band) needle blight of pine trees is caused by the fungus Dothistroma pini. The defoliation that occurs stunts growth and can lead to tree mortality. This disease has been widespread in Southern hemisphere plantation forests for several decades but recently severe epidemics have also occurred in the Northern hemisphere. The current method of control in many commercial forests is fungicide drift spraying, but there is pressure on forest industries to find alternatives.  Understanding the biology of the pathogen will assist in the development of new targeted methods of disease control.  One possible target for control is the non-host specific toxin dothistromin that is produced by the fungus. Dothistromin has been implicated as a pathogenicity factor as injection of purified toxin into pine needles reproduces the symptoms of disease.  Further to this is a concern that dothistromin itself could pose an environmental hazard due to its close similarity to a precursor of the highly carcinogenic metabolite, aflatoxin. Advances in our attempts to understand more about the production of dothistromin by the fungus, and to define its role in the plant-pathogen interaction, are presented.  

Functional genomics of Phytophthora -plant interactions

Sophien Kamoun

Department of Plant Pathology, The Ohio State University, Wooster, OH

The oomycete Phytophthora infestans causes late blight, a ravaging disease of potato and tomato. P. infestans is a hemibiotrophic pathogen that requires living host cells to establish a successful infection. Suppression of host defenses by P. infestans is thought to be a key pathogenicity mechanism, but remains poorly understood. Based on accumulating genome sequence data, we initiated functional genomic analyses of P. infestans interactions with tomato to gain insight into the process of host defense suppression. Our goal is to link sequences to phenotypes using computational tools for data mining and robust high throughput functional assays. In this presentation, I will focus on one example of this research. We used data mining of P. infestans sequence databases to identify 18 extracellular protease inhibitor genes, belonging to two major structural classes: (i) Kazal-like serine protease inhibitors (EPI1 to EPI14) and (ii) cystatin-like cysteine protease inhibitors (EPIC1 to EPIC4). Eight EPIs and EPICs were expressed in

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