Structural study at EMBL reveals how plants respond to water
shortages
Much as adrenaline coursing through our veins drives our body's
reactions to stress, the plant hormone abscisic acid (ABA) is behind
plants' responses to stressful situations such as drought, but how
it does so has been a mystery for years. Scientists at the European
Molecular Biology Laboratory (EMBL) in Grenoble, France, and the
Consejo Superior de Investigaciones Cientificas (CSIC) in Valencia,
Spain discovered that the key lies in the structure of a protein
called PYR1 and how it interacts with the hormone. Their study,
published online recently in Nature, could open up new approaches to
increasing crops' resistance to water shortage.
Under normal conditions, proteins called PP2Cs inhibit the ABA
pathway, but when a plant is subjected to drought, the concentration
of ABA in its cells increases. This removes the brake from the
pathway, allowing the signal for drought response to be carried
through the plant's cells. This turns specific genes on or off,
triggering mechanisms for increasing water uptake and storage, and
decreasing water loss. But ABA does not interact directly with
PP2Cs, so how does it cause them to be inhibited? Recent studies had
indicated that the members of a family of 14 proteins might each act
as middle-men, but how those proteins detected ABA and inhibited
PP2Cs remained a mystery – until now.
A group
of scientists headed by José Antonio Márquez from EMBL Grenoble and
Pedro Luis Rodriguez from CSIC looked at one member of this family,
a protein called PYR1. When they used X-ray crystallography to
determine its 3-dimensional structure, the scientists found that the
protein looks like a hand. In the absence of ABA, the hand remains
open, but when ABA is present it nestles in the palm of the PYR1
hand, which closes over the hormone as if holding a ball, thereby
enabling a PP2C molecule to sit on top of the folded fingers. As
these features seem to be conserved across most members of this
protein family, these findings confirm the family as the main ABA
receptors. Moreover, they elucidate how the whole process of stress
response starts: by binding to PYR1, ABA causes it to hijack PP2C
molecules, which are therefore not available to block the stress
response.
"If you treat plants with ABA before a drought occurs, they take
all their water-saving measures before the drought actually hits, so
they are more prepared, and more likely to survive that water
shortage – they become more tolerant to drought", Rodriguez
explains. "The problem so far", Márquez adds, "has been that ABA is
very difficult – and expensive – to produce. But thanks to this
structural biology approach, we now know what ABA interacts with and
how, and this can help to find other molecules with the same effect
but which can be feasibly produced and applied."
To determine the structure of PYR1, the scientists made use of
the infrastructure of the Partnership for Structural Biology,
including EMBL Grenoble's high-throughput crystallisation facilities
and the beamlines at the European Synchrotron Radiation Facility,
located in the same campus as EMBL Grenoble.
SOURCE: EMBL