Two Genes Crucial for Plants Colonizing the Earth 470 Million Ago Have Been Identified

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Pro Plyd

Jun 29, 2022, 4:35:24 PM6/29/22

Researchers from the University of Copenhagen have shed new light on
how plant life got established on the surface of our planet. They
demonstrated that two genes are crucial for terrestrial plants to protect
themselves against fungal attack – a defense mechanism that dates back
470 million years. These defenses most likely paved the way for all
terrestrial plant life.

Plants evolved from aquatic algae to being able to survive on land roughly
half a billion years ago, laying the groundwork for life on land. Fungi were
one of the obstacles that made this dramatic transition so difficult:

“It is estimated that 100 million years prior, fungi crept across Earth’s
in search of nourishment and most likely found it in dead algae washed up
from the sea. So, if you, as a new plant, were going to establish yourself on
land, and the first thing you encountered is a fungus that would eat you, you
needed some sort of defense mechanism,” says Mads Eggert Nielsen, a
biologist at the University of Copenhagen’s Department of Plant and
Environmental Sciences.

According to Mads Eggert Nielsen and his research colleagues from the
Department of Plant and Environmental Sciences and the University of
Paris-Saclay, the essence of this defense mechanism can be narrowed
down to two genes, PEN1 and SYP122. Together, they help form a kind of
plug in plants that blocks the invasion of fungi and fungus-like organisms.

“We found out that if we destroy these two genes in our model plant thale
cress (Arabidopsis), we open the door for pathogenic fungi to penetrate. We
found that they are essential to form this cell wall-like plug that defends
against fungi. Interestingly, it appears to be a universal defense mechanism
that is found in all terrestrial plants,” says Mads Eggert Nielsen, senior
author of the study, which is published in the journal eLife.

The research team has tested the same function in liverwort, a direct
descendant of one of Earth’s very first land plants. By taking the two
corresponding genes in liverwort and inserting them into thale cress, the
researchers examined whether they could identify the same effect. The
answer was yes.
Plant SYP12 syntaxins mediate an evolutionarily conserved general immunity
to filamentous pathogens

Filamentous fungal and oomycete plant pathogens that invade by direct
penetration through the leaf epidermal cell wall cause devastating plant
diseases. Plant preinvasive immunity toward nonadapted filamentous
pathogens is highly effective and durable. Pre- and postinvasive immunity
correlates with the formation of evolutionarily conserved and cell-autonomous
cell wall structures, named papillae and encasements, respectively. Yet,
it is
still unresolved how papillae/encasements are formed and whether these
defense structures prevent pathogen ingress. Here, we show that in
Arabidopsis the two closely related members of the SYP12 clade of syntaxins
(PEN1 and SYP122) are indispensable for the formation of papillae and
encasements. Moreover, loss-of-function mutants were hampered in
preinvasive immunity toward a range of phylogenetically distant nonadapted
filamentous pathogens, underlining the versatility and efficacy of this
Complementation studies using SYP12s from the early diverging land plant,
Marchantia polymorpha, showed that the SYP12 clade immunity function has
survived 470 million years of independent evolution. These results suggest
that ancestral land plants evolved the SYP12 clade to provide a broad and
durable preinvasive immunity to facilitate their life on land and pave the
to a better understanding of how adapted pathogens overcome this
ubiquitous plant defense strategy.

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