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Howard Judelson's background
education and interests

The oomycetes
learn more about these exciting organisms

The late blight disease
learn more about the problems that P. infestans causes

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Ongoing research projects

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Molecular genetics of
P. infestans: Transformation

Our laboratory has pioneered the development of transformation procedures for Phytophthora, starting in the early 1990s. 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.

Transformation is normally achieved using one of three drug-resistance markers. We have assisted many laboratories in establishing P. infestans transformation in their own facilities, and helped others to successfully transform other oomycetes including P. palmivora, P. parasitica, P. porri, P. sojae, and Saprolegnia.

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One of our transformation vectors.

An example of a recent project is shown below, where we developed a series of vectors for expressing fluorescently-tagged proteins P. infestans. These are useful for studying the targeting of proteins to different cellular locations.

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Expression of fluorescent markers with targeting signals in P. infestans. The proteins are all expressed from the ham34 promoter, and are named in the left margin. These include histone 2B fused at its C-terminus to mCherry (panels A, B), YFP with N-terminal calreticulin and C-terminal KDEL domains (C, D), GFP with N-terminal sequences from alpha-1,2-mannosidase (E, F), CFP with the SKL peroxisomal targeting motif (G, H), and the beta-subunit of ATPase fused to mCherry (I-K) or GFP (L-O).


Gene silencing is another tool that we employ. By introducing sense or antisense copies of a P. infestans gene into a transformant, frequently the expression of the native gene can be silenced (i.e. homology-dependent transcriptional silencing). This can be used to test the function of a gene. Recently, we systematically tested several variables associated with silencing in order to optimize the method.


inf1 silencing
The Inf1 gene was silenced using either sense, antisense, or hairpin constructs, which were introduced into transformants using protoplast, electroporation, or bombardment methods.


Bzip silencing

Analysis of transformants silenced for bZIP. A, Use of RT-PCR to identify silenced strains in transformants containing sense or antisense copies of the bZIP transcription factor. RT-PCR with actin primers was used as a control (not shown). B, Traces from movies of zoospores from representative silenced and non-silenced controls, representing zoospore movement over 4 seconds. C, interpretation of normal and wild type swimming behaviors.


Another example of a technology that have developed for oomycetes are inducible promoters, which can allow us to express genes in transformants at will.


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Induction of reporter gene using a synthetic methoxyfenozide-inducible promoter system.