Newly discovered 'scarecrow' gene might trigger big boost in food production
Cornell University |
With projections
of 9.5 billion people by 2050, humanity faces the challenge of feeding modern
diets to additional mouths while using the same amounts of water, fertilizer
and arable land as today. Cornell University researchers have taken a leap
toward meeting those needs by discovering a gene that could lead to new
varieties of staple crops with 50 percent higher yields.
The
gene, called Scarecrow, is the first discovered to control a special leaf
structure, known as Kranz anatomy, which leads to more efficient
photosynthesis. Plants photosynthesize using one of two methods: C3, a less
efficient, ancient method found in most plants, including wheat and rice; and
C4, a more efficient adaptation employed by grasses, maize, sorghum and
sugarcane that is better suited to drought, intense sunlight, heat and low
nitrogen.
"Researchers have been trying to find the underlying
genetics of Kranz anatomy so we can engineer it into C3 crops," said
Thomas Slewinski, lead author of a paper that appeared online in the journal Plant and Cell Physiology.
Slewinski is a postdoctoral researcher in the lab of senior author Robert
Turgeon, professor of plant biology.
The
finding "provides a clue as to how this whole anatomical key is
regulated," said Turgeon. "There's still a lot to be learned, but now
the barn door is open and you are going to see people working on this Scarecrow
pathway."
The
promise of transferring C4 mechanisms into C3 plants has been fervently pursued
and funded on a global scale for decades, he added.
If C4
photosynthesis is successfully transferred to C3 plants through genetic
engineering, farmers could grow wheat and rice in hotter, dryer environments
with less fertilizer, while possibly increasing yields by half, the researchers
said.
C3
photosynthesis originated at a time in Earth's history when the atmosphere had
a high proportion of carbon dioxide. C4 plants have independently evolved from
C3 plants some 60 times at different times and places. The C4 adaptation
involves Kranz anatomy in the leaves, which includes a layer of special bundle
sheath cells surrounding the veins and an outer layer of cells called
mesophyll. Bundle sheath cells and mesophyll cells cooperate in a two-step
version of photosynthesis, using different kinds of chloroplasts.
By
looking closely at plant evolution and anatomy, Slewinski recognized that the
bundle sheath cells in leaves of C4 plants were similar to endodermal cells
that surrounded vascular tissue in roots and stems.
Slewinski
suspected that if C4 leaves shared endodermal genes with roots and stems, the
genetics that controlled those cell types may also be shared. Slewinski looked
for experimental maize lines with mutant Scarecrow genes, which he knew
governed endodermal cells in roots.
When
the researchers grew those plants, they first identified problems in the roots,
then checked for abnormalities in the bundle sheath. They found that the leaves
of Scarecrow mutants had abnormal and proliferated bundle sheath cells and
irregular veins.
In all
plants, an enzyme called RuBisCo facilitates a reaction that captures carbon
dioxide from the air, the first step in producing sucrose, the energy-rich
product of photosynthesis that powers the plant. But in C3 plants RuBisCo also
facilitates a competing reaction with oxygen, creating a byproduct that has to
be degraded, at a cost of about 30-40 percent overall efficiency. In C4 plants,
carbon dioxide fixation takes place in two stages. The first step occurs in the
mesophyll, and the product of this reaction is shuttled to the bundle sheath
for the RuBisCo step. The RuBisCo step is very efficient because in the bundle
sheath cells, the oxygen concentration is low and the carbon dioxide
concentration is high. This eliminates the problem of the competing oxygen
reaction, making the plant far more efficient.
Source: Cornell University
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Posted by Unknown
on Friday, January 25, 2013.
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