IEF Final Report (298735 SYMBIONTS)
(3rd September 2012- 2nd September 2014)
Fungi and fungi-like microorganisms are thought to be of key
importance to the development of life on land. They entered
into relations with plants to varying degrees (SYMBIONTS),
helping plants colonize the land with major consequences for
the evolution of life on Earth. Their fossilised remains are
known to be preserved within the stems, roots and leaves of
plant fossils, yet they have not been systematically studied. My
goal was to determine the extent and nature of
microorganism/plant
associations
during
the
early
development of life on land. This was addressed by making
new use of historic collections of fossil plants in The Natural
History Museum, London.
Fly agaric, Amanita muscaria, forms mutualistic
relations with plants, especially with species of birch
and pine
Objectives
1. Undertake a novel systematics search of historic collections of fossil plants to locate plant-associated
saprophytes, symbionts and pathogens focussing on the earliest plants to live on land.
2. Describe the characteristics of the fungi and other microorganisms, including their life cycles, biology,
affinities, and their interactions with the plants using state of the art imaging methods.
3. Establish how they relate to living forms.
4. Understand the origin and evolution of key microorganism/plant associations and their significance to
the evolution of life on land.
SYMBIONTS website: http://www.nhm.ac.uk/research-curation/earth-sciences/fossil-plants/fossil-plantresearch/symbionts/index.html
Work carried out to achieve objectives
When plants become fossilised, their internal tissues are frequently
preserved in minerals, a process which also preserves associated
microorganisms. Fossil plants have been studied for over 100 years by
making thin sections, but the associated microbial remains have been mostly
overlooked. The first step of my research was to survey these historic fossil
plant slide collections for the microrganisms they contain. Because the
collections are so large (over 15,000 slides) my initial survey involved a
representative sample of 200 slides.
A thin section from the NHM
collection
These were examined using microscopy
(Leica M205C stereomicroscope ; Nikon Eclipse LV100ND compound
microscope). I found that each fossil plant slide contained a large number
of microorganisms, so a digital record was made of each significant find,
which can be linked back to the original microscope slide. Many of these
represent newly discovered organisms or newly discovered
plant/microorganism associations.
Section of the stem of a 407 million
year old plant showing fungal
colonization
In
addition
to
using
standard
microscopy, I used state-of-the art
Confocal Laser Scanning Microscopy (CLSM). This technique was
originally developed for use in biology to image in three dimensions the
structural components of living tissues and cells. This is the first
application of the technique to fossil fungi, enabling me to better
characterize their features and thereby their relations to living species. I
was able to obtain detailed three-dimensional images of fossil
microorganisms within 407 million year
old plants, which are among the earliest known plants to live on land.
407 million year old fungal spores
(Chytridiomycota) observed in confocal
laser scanning microscopy
Results
1. New microorganisms related to endomycorrhizal fungi: These are fungi that live symbiotically
within most plants today helping them to obtain nutrients from the soil. I discovered an important group
new to the fossil (Mucoromycotina) forming associations with the earliest plants. I was also able to show
that it lived together within the same plants as another group of endomycorrhizal fungi (Glomeromycota).
My results were presented at scientific meetings in 2014 : (1) 33th New Phytologist Symposium, Zurich
(Switzerland), (2) European Paleobotanical and Palynological Conference (Italy) and (3) International
Palaeontological Congress, Mendoza (Argentina). They were published recently in New Phytologist.
Results also formed part of a review paper on the evolution of roots published in Plant Physiology. These
are both leading international scientific journals.
2. New microorganisms related to chytrids: New associations were found between chytrid fungi
and the earliest plants. Results were presented at two international meetings in 2014 : (1) European
Paleobotanical and Palynological Conference (Italy) and (2) International Palaeontological Congress,
Mendoza (Argentina). A manuscript will be submitted for publication in November.
3. New microorganisms related to the oomycetes (water molds): Today this group includes some
important plant pathogens (e.g., Phytophthora infestans Potato Blight). My discoveries add to a growing
body of data indicating that oomycetes were an important component of microorganism diversity in early
land ecosystems. My longer term goal is to use these new data to show when key events in oomycete
evolution took place. Results were presented at three international meetings in 2013 and 2014: (1) The
Botanical Society of America (USA), (2) Agora Palaeobotanica Arino (Spain) and (3) Oomycete
Molecular genetics network meeting (UK). They are being prepared for publication.
Conclusions
1. The reliance of plants on fungi to obtain nutrients from the soil (i.e., endomycorrhizae) dates back to
their earliest known land-dwelling ancestors. It involved ancestors of major groups of living fungi,
including Glomeromycota and Mucoromycotina.
2. The earliest plants had no roots. Their endomycorrhizae functioned in a way that was more similar to
primitive living plants called liverworts than to more complex living forms such as ferns and conifers.
3. Oomycetes, which include serious pathogens of modern plants, were diverse in the earliest plant
communities. However, it is likely that the earliest oomycetes were not pathogens.
4. Historic slide collections of fossil plants are an important new source of information on the evolution
of microorganisms associated with plants.
Potential impact and use of results
1. Scientific Community : Results are principally of interest to the scientific community. They will help
establish when important groups of fungi and oomycetes evolved and how with plants they influenced the
evolution of key Earth Systems (e.g., the carbon cycle). Together with colleagues in the UK and France, I
obtained funding (£10,000 New Phytologist Trust) to host an international workshop on the co-evolution
of plants and fungi, which was held at NHM (London) in September 2014. One outcome is that we are
working with French and American colleagues to develop an interdisciplinary reserach project bridging
palaeontology and genomics. A second outcome is an invitation to write a major review paper for New
Phytologist on this topic.
I gave five seminars directed to students and colleagues in UK, France and Estonia
2. Civic Society : I wrote an article for Jardins de France, the journal of the Société Nationale
d’Horticulture de France which was published in May 2013 and I co-authored an article for the popular
French Scientific magazine La Recherche on this research, which was publised in November 2013 and.
My work has been presented to the public at several outreach events in The Natural History Museum
(London) and at four other venues in the UK.