IEF Periodic Report (298735 SYMBIONTS)
(3rd September 2013- 2nd September 2014)
Fungi and fungi-like eukaryotes are thought to be of
key importance to the early development of terrestrial
ecosystems. These microorganisms entered into
relations
with
plants
in
varying
degrees
(SYMBIONTS), which facilitated the colonization of
the land having a major impact on the evolution of life
on Earth. Their fossilised remains are often preserved
within the stem, root and leaf tissues of plant fossils. I
undertook the first systematic survey of microscopic
eukaryotes based on the historic fossil plant collections
of The Natural History Museum, London. The
overarching goal was to reveal and understand the
significance of microorganism/plant associations during
the early development of land ecosystems.
Fly agaric, Amanita muscaria, forms mutualistic
symbiosis especially with species of Betula
(birch) and Pinus (pine).
Project Objectives
1. Undertake a novel investigation of microscopic eukaryote plant saprophytes, symbionts and
pathogens in early terrestrial ecosystems.
2. Document details of the morphology in these microscopic eukaryotes to characterise their life
cycles, biology, and affinities, using state of the art imaging methods.
3. Develop phylogenetic characters for the newly described microorganisms in order to place them
into a phylogenetic framework and relate them to modern forms.
4. Establish a better understanding of the origin and evolution of key microorganism/plant associations
and their significance during the early development of land ecosystems.
SYMBIONTS website : http://www.nhm.ac.uk/research-curation/earth-sciences/fossil-plants/fossilplant-research/symbionts/index.html
Description of the work performed since the beginning of the project
Living plants contain numerous and varied fungi and fungi-like
eukaryotes as symbionts, parasites or pathogens. When plants become
fossilised, their internal tissues are frequently preserved in minerals
(permineralization), a process which also preserves associated
microbes. Fossil plants have been studied for over 100 years by making
thin sections of their permineralized tissues, 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
their microbial component, using state of the art microscopy. Because A thin section from the NHM
the collections are so large (over 15,000 slides) my initial survey collection
involved a representative sample of 200 slides.
Transverse section of an axis of
the plant Rhynia gwynnevaughanii
showing
fungal
colonization
To undertake the initial survey I received training in the use of a Leica
M205C stereomicroscope and a Nikon Eclipse LV100ND compound
microscope and associated imaging software. I found that each fossil
plant slide contained a significant microbial component, including
oomycetes, mycorrhizal fungi in the Glomeromycotina and the
Mucoromycotina, other fungi such as Chytridiomycota as well as
other eukaryotes. A digital record was made of each significant find,
which can be linked to the original microscope slide. Many of these
represent newly discovered organisms or newly discovered
plant/fungi associations.
In addition to using standard microscopy to survey and provide a
basic digital record of new finds (above), 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 tissues and cells, and it
has not been widely employed on fossils. My work involved a
novel application of the technique, which I used to better enable
me to characterize early fossil microbes and to establish their
relations to living groups. I received training in the use of a
Nikon A1-Si laser-scanning confocal microscope and associated
software. Results enabled me to obtain detailed threedimensional images of fossil microorganisms over 400 million
years old (e.g. algae, oomycetes, fungi).
400 million year old fungal spores
(Chytridiomycota) observed in confocal
laser scanning microscopy
Description of the main results achieved
1. New fungi discovered in the earliest known plants : I found new endomycorrhizal fungi in 407
million year old fossil plants from Scotland (UK). I showed that fungi colonised both the aerial stems
and the basal parts of the fossil plant Horneophyton lignieri. Critical comparisons between the new
endophytes, previously known fossil species, and related living forms in clubmosses and bryophytes
revealed several features of both Mucoromycotina and Glomeromycota fungal groups. My results
show (1) that early fossil plants could be colonised by at least two different types of fungi and (2) that
the diversity of early fungal associations is far more extensive than assumed hitherto, overturning the
long held paradigm that these symbionts were exclusively glomeromycotes. Results were published in
New Phytologist and contributed to a review paper in Plant Physiology, both leading international
scientific journals. Results on fungal colonisation in the fossil plant Asteroxylon mackeiei will be
submitted shortly. They were presented at international meetings in 2014: (1) European Paleobotanical
and Palynological Conference (Italy) and (2) International Palaeontological Congress, Mendoza
(Argentina).
2. Oomycetes : These microscopic heterotrophic eukaryotes include some important plant pathogens
(e.g., Phytophthora infestans Potato Blight). Their evolutionary history is mostly inferred indirectly
from studies of living species (molecular phylogenetics). I discovered new early fossil oomycetes
demonstrating that these were an important component of microorganism diversity in early terrestrial
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 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.
Final results and their potential impact and use
My research is leading to a new understanding of the diversity and function of fungi and fungi-like
eukaryotes during the early evolution of life on land. Results help us to understand the early evolution
of plant symbionts and pathogens. They are of crucial importance in calibrating the fungal and
oomycete tree of life. They are also important in our understanding of how plants and fungi act
together to influence key earth systems, such as the carbon cycle. Following a workshop funded by the
New Phytologist Trust that I co-organised at the Natural History Museum, I am building an
interdisciplinary research network with French and American colleagues to bridge palaeontology and
genomics. I have been invited with my co-organisers to write a major review on this topic for New
Phytologist (Transley Review). Reviews of this type are the perfect starting point to get an
authoritative overview of a topic because they are written in a way that is accessible to a nonspecialist.