General and contact information
Howard Judelson's background
education and interests
learn more about these exciting
The late blight disease
learn more about the problems that P. infestans causes
Ongoing research projects
Other lab members
Opportunities for graduate study in the lab
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.
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.
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.
The Inf1 gene was silenced using either sense, antisense, or hairpin constructs,
which were introduced into transformants using protoplast, electroporation, or bombardment
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.
Induction of reporter gene using a synthetic methoxyfenozide-inducible promoter system.