permaculture

[Lawrence London <lfljvenaura@gmail.com>]

Researchers make discovery that could increase plant yield in wake of
looming phosphate shortage.
https://phys.org/news/2017-03-discovery-yield-looming-phosph.html#nRlv

Scientists at the University of North Carolina at Chapel Hill have
pinpointed a key genetic switch that helps soil bacteria living on and
inside a plant's roots harvest a vital nutrient with limited global supply.
The nutrient, phosphate, makes it to the plant's roots, helping the plant
increase its yield.

The work, published in the March 15 issue of *Nature*, raises the
possibility of probiotic, microbe treatments for plants
<https://phys.org/tags/plants/> to increase their efficient use of phosphate
<https://phys.org/tags/phosphate/>. The form of phosphate plants can use is
in danger of reaching its peak - when supply fails to keep up with demand -
in just 30 years, potentially decreasing the rate of crop yield as the as
the world population continues to climb and global warming stresses crop
yields, which could have damaging effects on the global food supply
<https://phys.org/tags/global+food+supply/>.

"We show precisely how a key 'switch protein',PHR1, controls the response
to low levels of phosphate, a big stress for the plant, and also controls
the plant immune system," said Jeff Dangl, John N. Couch Distinguished
Professor and Howard Hughes Medical Institute Investigator. "When the plant
is stressed for this important nutrient, it turns down its immune system so
it can focus on harvesting phosphate from the soil. Essentially, the plant
sets its priorities on the cellular level."

Dangl, who worked with lead authors, postdoctoral researchers Gabriel
Castrillo and Paulo José Pereira Lima Teixeira, graduate student Sur
Herrera Paredes and research analyst Theresa F. Law, found evidence that soil
bacteria <https://phys.org/tags/soil+bacteria/> can make use of this
tradeoff between nutrient-seeking and immune defense, potentially to help
establish symbiotic relationships with plants. Bacteria seem to enhance
this phosphate stress response, in part simply by competing for phosphate
but also by actively 'telling' the plant to turn on its phosphate stress
response.

In recent plant biology studies, there have been hints of a relationship
between plant phosphate levels and immune system activity - a relationship
that some microbes can manipulate. In the new study, Dangl and colleagues
delved more deeply into this relationship, using mutant versions of
Arabidopsis thaliana, a weed that has long been the standard "lab rat" of
plant biology research.

In one experiment, Dangl's team found that Arabidopsis plants with mutant
versions of the PHR1 gene not only had impaired phosphate stress responses,
but also developed different communities of microbes in and around their
roots when grown in a local native North Carolina soil. This was the case
even in an environment of plentiful phosphate - where phosphate competition
wouldn't have been a factor - hinting that something else was happening in
the plants to trigger the growth of different microbial communities. The
researchers found similar results studying PHL1, a protein closely related
to PHR1 with similar but weaker functions.

In another experiment, in lab-dish conditions, the researchers colonized
roots of sterile-grown normal Arabidopsis plants with a set of 35 bacterial
species isolated from roots of plants grown previously in the same native
soil. In these re-colonized plants, the phosphate stress response increased
when exposed to a low-phosphate condition.

Investigating further, the team showed that PHR1 - and probably to a lesser
extent PHL1 - not only activates the phosphate stress response
<https://phys.org/tags/stress+response/> but also triggers a pattern of
gene expression that reduces immune activity, and thus makes it easier for
resident microbes to survive.

The findings suggest that soil-dwelling microbes have figured out how to
get along with their plant hosts, at least in part by activating PHR1/PHL1
to suppress immune responses to them. Dangl's team also thinks these
microbes may even be necessary for plants to respond normally to
low-phosphate conditions. It could be possible, then, to harness this
relationship - via probiotic or related crop treatments - to enable plants
to make do with less phosphate.

"Phosphate is a limited resource and we don't use it very efficiently,"
said Dangl, who is also an adjunct professor of microbiology and immunology
at the UNC School of Medicine. "As part of fertilizer, phosphate runs off
into waterways where it can adversely affect river and marine ecosystems.
It would be better if we could use phosphate in a way that's more
efficient."


Read more at:
https://phys.org/news/2017-03-discovery-yield-looming-phosph.html#jCp