ICOM1 Abstract
session 5
Delp, Gabriele1, Sally E. Smith2, Susan. J. Barker1. 1Dept. of Plant
Science and 2Soil Science, Waite Campus, University of Adelaide, Glen
Osmond, S.A. 5064, Australia. - Two differential display products from
the VA fungus G. intraradices: one contains a homeobox, the other shows
homology to a human thyroid receptor-interacting protein.
In our molecular study of the mycorrhizal symbiosis between barley and
Glomus intraradices we are using the differential display technique to
identify genes that are differentially expressed in mycorrhizal roots.
Roots with uniform infection stages were produced using the nurse pot
method. This inoculation method, which allows a rapid synchronised
infection of the roots by transplantation of seedlings into pots with an
established inoculum, has revealed that establishment of the mycorrhiza
involves a uniform, reproducibly timed series of developmental events.
We used mRNA from an early infection stage prior to the development of
arbuscules as the template for differential display, compared to non-
mycorrhizal root mRNA at the same stage after transplantation. Using
this material, several PCR products were consistently differentially
amplified in the differential display reaction. Sequence analysis of two
of the fragments obtained from infected roots revealed homologies to
regulatory genes from higher eucaryotes: one (dd11) contains a homeobox,
which indicates that it binds DNA and may act as a transcriptional
regulator; the other (dd5) shows homology to trp 15, a human protein
that interacts in a hormone-dependant manner with the thyroid receptor.
PCR with primers specific for dd5 and dd11 using G. intraradices and
barley DNA as templates showed that the differential display products
are of fungal origin. Using the same specific primers, fragments of the
expected size can be amplified from total and mRNA of infected but not
uninfected barley roots for both dd5 and dd11, which indicates that the
corresponding genes are expressed during intraradical growth of G.
intraradices. Our results show that differential display is a suitable
technique to obtain cDNA sequences from fungal genes that are expressed
during VA mycorrhizal interaction. These products will be used to
isolate the corresponding genes to allow a more detailed study of their
expression pattern and function.