MEDIA STATEMENT
Friday 17th July 2015
A 400 MILLION YEAR OLD SIGNALLING SYSTEM IN PLANTS
Research by an award winning plant scientist suggests that KAI2-dependent signalling is ancient and
fundamental to all plants.
The KAI2 signalling system controls many aspects of the plant life cycle, and a recently published study by
2015 Goldacre Award recipient Dr Mark Waters and his colleagues adds further support for its critical
importance in plants by revealing its very ancient origins.
The study, published this week in the journal The Plant Cell, shows that the cell signalling system likely
evolved at least 400 million years ago and has been maintained by plants ever since.
Dr Waters was awarded the prestigious Goldacre prize by the Australian Society of Plant Scientists in
recognition of his significant efforts in identifying and determining the importance of the KAI2-dependent
signalling system in plants. Dr Waters first discovered the KAI2 protein as a means for plants to re-germinate
after fire. It subsequently became clear that KAI2 signalling played many more fundamental roles in plants.
The seeds of many plants can be stimulated to germinate after exposure to burnt vegetation and smoke due to
the release of chemical compounds called karrikins. The KAI2 protein allows plants to detect these karrikins.
The ability to perceive smoke signals makes evolutionary sense for plants that live in fire-prone areas, but a big
puzzle was why species that never experience fire should respond to karrikins. Subsequent observations that
plants lacking KAI2 have a number of developmental issues suggested a greater importance for this protein in
plants.
“In plants lacking KAI2, seeds germinate late, seedlings grow abnormally tall, and leaves fail to form the correct
shape,” said Dr Waters. “We knew that KAI2 was important, and not just for sensing karrikins. To us, it looked
like these mutant plants were missing something critical for normal plant development.”
Results from the most recent study suggest that the KAI2-dependent signalling system not only performs
fundamental roles in plants but that it also originated many years ago.
“500 million years ago plants were simple in form and never strayed far from water,” said Dr Waters. “Over
time, evolution solved many of the challenges of living on dry land in a stepwise fashion, culminating in the
highly diverse and specialised flowering plants that now dominate most of Earth’s ecosystems.”
When Dr Waters noticed that liverworts, mosses and lycophyte ferns, the most primitive land plants, have
KAI2-like proteins, he set out to study these proteins further. The lycophyte fern Selaginella moellendorffii,
which has recently had its genome fully sequenced, was the plant model of choice for this work.
The study revealed that a KAI2-like protein from Selaginella does indeed have KAI2-like properties, but with
one exception: it does not work with karrikins.
“It worked beautifully in restoring leaf shape and seedling growth, suggesting that it does the same things in
recent plants as it does in Selaginella,” said Dr Waters. “But with karrikins, no dice. So we think KAI2 has a
very fundamental signalling function that is common to ferns and higher plants, but things like responding to
karrikins likely evolved much later.”
Lycophyte ferns and flowering plants last shared a common ancestor some 200 million years before dinosaurs
existed, but this study suggests KAI2 was already in existence at this time. The fact that KAI2-dependent
signalling has existed over such long timescales implies that it holds a centrally important function in plant
development.
Dr Waters believes that KAI2 may be the receptor for an unknown plant hormone, and that some plants have
managed to use it to detect smoke as well.
“Evolution is pretty efficient,” he says. “Tinkering with a pre-existing system is much easier than coming up
with something anew.”
This work was published in The Plant Cell.
The study was performed out of the Australian Research Council Centre of Excellence in Plant Energy Biology
and the University of Western Australia’s School of Chemistry and Biochemistry, where Dr Waters holds a joint
research position.
MEDIA REFERENCE
Karina Price (ARC CoE in Plant Energy Biology, Science Communications Officer)
(+61 8 6488 4481)
Image: Dr Mark Waters with a kai2 mutant research plant.
Image credit: The ARC CoE in Plant Energy Biology