CEPCEB Members

Howard S. Judelson Professor Department of Plant Pathology University of California Riverside, CA 92521 Phone: (951) 827-4199 Fax: (951) 827-4294 Areas of Expertise Developmental Biology Plant-microbe Interactions Signal Transduction Oomycete Biology
Background Asexual Sporulation Sexual Sporulation Phytophthora Genomics Current Laboratory Personnel Selected Publications Related to Spore Biology (Bibliography page) Selected Publications Related to Phytophthora Genetics and Genomics (Bibliography page)

Background

After receiving a B.S. degree in Biochemistry from Cornell University, I moved to the University of Wisconsin-Madison where I received my Ph.D. in Molecular and Cellular Biology. My thesis research involved studying the developmental biology of a slime mold, Dictyostelium discoideum, with a focus on the regulation of post-translational glycosylation of lysosomal enzymes. I then moved to the University of California-Davis, where I pursued postdoctoral research studying the lettuce downy mildew pathogen, Bremia lactucae. I then began to study various Phytophthora species in the NSF Center for Engineering Plants for Resistance Against Pathogens (CEPRAP) at Davis. In 1994 I came to the University of California-Riverside, where I am an Associate Professor in the Plant Pathology Department.

The goals of our lab at Riverside are to further our understanding of the developmental biology, genetics, and pathology of oomycetes, a group of fungal-like algae found throughout the world. Most of our studies involve Phytophthora infestans, which causes the destructive late blight diseases of potato and tomato.

The late blight diseases have always been important, but became especially difficult over the past decade. The worldwide cost of the potato disease alone exceeds $5 billion per year. This is enough to purchase potatoes to fulfill the caloric needs of the entire world for 2.7 days, based on 2200 Kcal/day and current U.S. potato prices!

To the left:
P. infestans caused the Irish potato famine in the mid-1800's, which lead to the death of 1 million people. This historical picture--from the time of the famine--shows a woman and child trying to find some non-blighted potatoes to eat.

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Asexual Sporulation

Much of our laboratory's research examines the asexual spores of P. infestans, which play a very important role in the disease cycle. The spores serve as the primary inoculum for epidemics caused by P. infestans, as with most fungi. Many generations of the asexual cycle occur per season, spreading disease through a field. Conditions that suppress asexual sporulation can control late blight and related diseases by breaking this cycle. Consequently, identifying factors that control sporulation, plus ways to interrupt the normal cell cycle, will lead to new strategies for crop protection.

Asexual Sporangia

A few of the questions that we are trying to answer in our studies of asexual sporulation are: What genes and proteins are required for forming spores? What is the metabolic/cellular trigger of sporulation? How is the pattern of transcription altered in hyphae to "turn on" the genes expressed during sporulation? What sequence elements within promoters are required for spore-specific patterns of expression?

To date, approximately 130 genes specifically expressed in spores have been identified through array studies and by mining genomics databases. Current work involves analyzing the function of the genes, using the tools of genetics, biochemistry, and cell biology. Most of our current work is focusing on genes that may play regulatory roles during sporulation, such as protein kinases, protein phosphatases, and transcription factors. We are also interested in understanding the mechanisms that regulate the activation of these genes in spores.

Partial results of microarray study identifying genes up-regulated in sporangia versus hyphae (SPOR).
	Use of promoter-GUS fusions to study activity of sporulation-induced promoter. A promoter from the pumilio gene was fused to the GUS reporter gene and transformed into P. infestans. Expression begins within young sporangiophores, at the initial stages of the sporulation pathway.

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Sexual Sporulation

We are also interested in the mechanisms by which the sexual spores, also known as oospores, are formed in Phytophthora. Such spores play important roles in disease since they can survive harsh environments to initiate epidemics in subsequent seasons. Using subtraction cloning and array studies, we have identified several genes believed to play important roles in regulating sexual development.

Mating involving wild type strain and a transformant expressing a fusion between the promoter of a mating-induced gene and the GUS reporter gene. Transcription of the gene is activated early in the pathway, as evidenced by its expression in the young oogonium (left panel).

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Phytophthora Genomics

(Protocol for silencing genes P. infestans using transformation)

We are involved in several projects that address the structural and functional genomics of P. infestans. Through a variety of collaborations, we have generated >90,000 expressed sequence tags (ESTs) from all phases of P. infestans development. Such data has been used to generate microarrays for P. infestans, which we are using to identify development- and nutrition-regulated genes. The ESTs will also be used to annotate the P. infestans genome. A 1X sequence of the P. infestans genome has already been obtained and, in collaboration with researchers at MIT, Cornell, and Ohio State, a project to complete the genome is now on track.

Our laboratory has pioneered the development of transformation procedures for Phytophthora. By "transformation" we mean the introduction of DNA into an organism, for the purpose of expressing a novel gene, expressing higher levels of a native gene, or silencing the expression of a native gene.

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Current Laboratory Personnel

• Cristina Cvitanich, postdoc
• Audrey Ah Fong, postdoc
• Shuji Tani, postdoc
• Flavio Blanco, postdoc
• Waraporn Prakob, graduate Student
• Kyoung Su Kim, graduate Student

Selected Publications Related to Spore Biology (Bibliography page)

Selected Publications Related to Phytophthora Genetics and Genomics (Bibliography page)

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