Michigan Tech researchers are transferring altered genes into
fungi that facilitate the flow of nutrients through tree roots to help trees
protect themselves against disease and insects.
April 25, 2000 / Michigan Technological University
HOUGHTON, MI -- Researchers at Michigan Tech are transferring altered genes
into fungi that facilitate the flow of nutrients through tree roots to help
trees protect themselves against disease and insects.
Using "doctored" genes to impart desired characteristics into fungi that
live symbiotically with tree roots can ultimately help trees grow faster and
live healthier lives, according to Project Leader Dr. Gopi Podila, a
molecular biologist in Michigan Tech's Department of Biological Sciences.
"Ectomycorrhizal (on top of the root) fungi provide a major network in the
soil for making nutrients available to tree root systems," explains Podila.
"By breaking down minerals locked up by acidic soils caused by the
decomposition of needles, leaves, and other forest litter, fungi facilitate
the passage of those nutrients from the soil to the tree. The fungus, in
turn, draws food from the tree, enhancing its own survival. Another benefit
of this symbiotic relationship is that the fungus can grow wider and deeper
into the soil -- and this greatly increases the outreach of the tree in its
search for essential minerals."
Podila says that normally when you try to put a fungus on a plant, the two
try to kill one another, but fortunately this mutually beneficial
relationship has evolved in nature over the course of millions of years.
"One of the things we want to determine," he says, "is how they communicate
with one another -- how do they each let the other know that they are
friendly."
He says the process is a long one.
"It's almost like a courtship. The fungus gradually approaches the tree root
system and this can take as long as three or four months. And even then, the
fungus is 'turned on' only to specific host signals. The fungus prepares
itself to form the association with the host plant by expressing specific
symbiosis-related genes. These genes are turned on by the right plant
signals, and this process is controlled by DNA sequences called 'promoters.'
These promoters are responding to plant signals and determine the
symbiosis-related expression of genes. If we can combine a specific gene
with the right promoter, we can introduce a variety of genes into the
fungus, where they will express their specific qualities to enhance the life
of the tree."
Podila says the fungus provides a protective "coating" around the tree's
roots, protecting it from drought and attack by various microbial pathogens.
"Reforestation techniques use herbicides to prevent grass and weeds from
covering up the reforested area and forming competition for tree seedlings,"
he says. "Insect pests, such as the white grub, which normally feed on grass
roots, must then turn to tree roots for food. White grubs are voracious
eaters that can completely chew away the roots of a young tree, leaving it
unable to draw nutrients from the soil. We can prevent this from happening
by altering the mycorrhizal fungus so it will produce insecticidal proteins
that are unpalatable to the grubs, causing them to avoid the tree roots. The
protein produced by the altered gene is biodegradable and completely
harmless to humans." If these genes are put under the control of
symbiosis-related gene promoters, then their expression will be limited to
mycorrhizal roots and thus will not cause any unintended expression of these
genes.
Podila says it is also possible to improve the ectomycorrhizal fungi to
reduce the uptake of soluble metals by tree roots. He says this will be very
useful in alleviating conditions caused by acid pollution and aluminum
toxicity.
"The use of genetically-improved mycorrhizal fungi is a novel and feasible
approach for increasing forest biomass," says Podila. "This system, when
fully developed, also has the potential to be adapted to handle a variety of
problems associated with plant health, and could lead to further research
that will use mycorrhizal fungi to help the plant host in many beneficial
physiological and ecological ways."
(posted without permission)
