Symbiotic Fungi: Principles and Practice (Soil Biology)

Foreword
So old, so new...
More than 450 million years ago, plants and fungi associated to produce a
mutually beneficial symbiosis that assisted plants to invade the terrestrial environment,
which was poor in nutrients and subject to desiccation and full sunlight. This
is one of the main lessons that fossil records have transmitted to us, thanks to the
reports of many paleontologists, starting with Kidston and Lang (1921). Their
wonderful observations, which have been confirmed by many others, provided
the evolutionary background to understand how mycorrhizas are a powerful driving
force for the functioning of ecosystems, supplying land plants with phosphorus and
nitrogen, as well as fungi with carbon, which finally accumulates in the soil.
On the other hand, few biological issues have entered the mainstream of biology
in such a vigorous way as mycorrhizas. Mainly thanks to DNA technologies and
genomics, new tools to discover symbiont communication, development and diversity
and to reveal the contribution of each partner to the functioning of the association
have been deciphered, thus offering breakthrough findings. Looking at the
history of mycorrhizas, it can be seen that some very important events have marked
recent years: the first sequenced genome of Laccaria laccata (Martin et al. 2008)
opened a window on the secrets of ectomycorrhizal fungi thriving in forests and
associated with woody plants; the identification of the plant genes that control the
signal transduction pathways in arbuscular mycorrhizal (AM) legumes has allowed
us to dissect the crucial steps of the fungal colonization process (Parniske 2008); the
discovery that plant molecules, strigolactones, are perceived by AM fungi and act
as ‘‘branching factors’’ (Akiyama et al. 2005) represents a landmark in our knowledge,
but has also led to a second very recent discovery. Strigolactones have been
found to impact the plant phenotype, representing a novel class of endogenous plant
hormones that are present in a wide range of angiosperms from Arabidopsis
thaliana to rice (Gomez-Roldan et al. 2008; Umehara et al. 2008).
But mycorrhizas also go beyond the issue of plant/fungal biology by occupying
new fields, like that of environmental microbiology, and by pushing the development
of new approaches, like those required for metagenomics. While the foundation set up
by Craig Venter, the world-renowned genome research pioneer (www.jcvi.org/),
v