Adelaide, South Australia
July 8, 2009
An international team of
scientists has developed salt-tolerant plants using a new type
of genetic modification (GM), bringing salt-tolerant cereal
crops a step closer to reality.
The research team - based at the
University of Adelaide's
Waite
Campus - has used a new GM technique to contain salt in
parts of the plant where it does less damage.
Salinity affects agriculture worldwide, which means the results
of this research could impact on world food production and
security.
The work has been led by researchers from the
Australian Centre for Plant
Functional Genomics and the University of Adelaide's
School of Agriculture,
Food and Wine, in collaboration with scientists from the
Department of Plant
Sciences at the University
of Cambridge, UK.
The results of their work are published today in the top
international plant science journal,
The Plant Cell.
 "Salinity
affects the growth of plants worldwide, particularly in
irrigated land where one third of the world's food is produced.
And it is a problem that is only going to get worse, as pressure
to use less water increases and quality of water decreases,"
says the team's leader,
Professor Mark Tester, from the School of Agriculture, Food
and Wine at the University of Adelaide and the Australian Centre
for Plant Functional Genomics (ACPFG).
"Helping plants to withstand this salty onslaught will have a
significant impact on world food production."
Professor Tester says his team used the technique to keep salt -
as sodium ions (Na+) - out of the leaves of a model plant
species. The researchers modified genes specifically around the
plant's water conducting pipes (xylem) so that salt is removed
from the transpiration stream before it gets to the shoot.
"This reduces the amount of toxic Na+ building up in the shoot
and so increases the plant's tolerance to salinity," Professor
Tester says.
"In doing this, we've enhanced a process used naturally by
plants to minimise the movement of Na+ to the shoot. We've used
genetic modification to amplify the process, helping plants to
do what they already do - but to do it much better."
The team is now in the process of transferring this technology
to crops such as rice, wheat and barley.
"Our results in rice already look very promising," Professor
Tester says.
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A
comparison of genetically modified (GM) plants and
non-GM plants grown in saline conditions: (above)
non-GM plants struggling to grow in saline
conditions; (below) GM plants thriving in the same
conditions.
Image courtesy of the Australian Centre for Plant
Functional Genomics (ACPFG)/University of Adelaide.
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Professor Mark Tester photo by
Chris Tonkin. |
Source:
CropBiotech Update
The Earth is one salty planet.
About 70 percent of its surface is covered with water, and more
than 95 percent of that water contains 35 grams of sodium
chloride per liter. The accumulation of this salt in cultivated
fields has been a problem since the beginning of agriculture.
While irrigation has made it possible to extend agriculture to
semi-arid and arid areas of land, it has also resulted in
large-scale water logging and salinity. Evaporation of irrigated
water leaves behind salt which accumulates over time. Land
degradation due to increased salinity presently affects more
than 20% of all irrigated land in at least 100 countries.
High soil salinity negatively affects the growth of many crops.
Salt, for example, decreases the availability of water in the
soil. Accumulation of excess salt ions in plant cells is also
fatal. These ions can impair the activity of plant enzymes,
inhibit photosynthesis and damage the cell membrane. Development
of crop varieties resistant to salinity is an important strategy
to sustain food production in many parts of the world.
Recently, a team of researchers from the Australian Center for
Plant Functional Genomics (ACPFG) and the University of
Adelaide's School of Agriculture, Food and Wine, developed
salt-tolerant plants using a novel approach, bringing
salt-tolerant crops a step closer to reality.
Their work appears in the current issue of the journal Plant
Cell.
"More than 800 million hectares of land throughout the world are
salt affected," said Mark Tester, leader of the study and
professor at the University of Adelaide. "This amount accounts
for more than 6 percent of the world's total land area."
Tester and colleagues focused on a transporter, a
membrane-embedded protein that moves ions in and out of the
plant cell. This particular transporter, called HKT1;1, mediates
salinity tolerance by retrieving sodium ions (Na+) from the
transpiration stream, therefore reducing the levels of Na+ in
the shoot. The gene that encodes for the transporter is
particularly expressed around the plant's water conducting
pipes. Mutants that lack this gene were found to be salt
sensitive.
They developed Arabidopsis plants that over-express HKT1;1 in
the pericycle and vascular bundle of the stele of mature roots.
Na+ transport was monitored using radiolabeled sodium (22Na+).
The scientists found that over-expression of HKT1;1 in the stele
reduced sodium accumulation in shoot by up to 64 percent. By
contrast, they found that plants constitutively expressing the
gene accumulated high levels of sodium in the shoot and grew
poorly. When grown in a medium supplied with 100 mM of NaCl, the
transgenic plants that over-express HKT1;1 in stelar root cells
continued to thrive, whereas their non-transgenic counterparts
as well as plants that constitutively express the transporter
gene exhibited signs of salt stress.
The study demonstrates that manipulating transport processes in
specific plant cells may be more effective in modifying the
accumulation of solutes in the plant than manipulating these
processes indiscriminately.
According to Tester, the same approach has been used to increase
nitrogen use efficiency of crops. "We have also successfully
used this approach to increase the delivery of iron and zinc to
the endosperm of rice grains," says Tester. "I think it could
also be used to increase the efficiency of phytoremediation."
The team is now in the process of applying this approach to
develop salt-tolerant cereal crops.
"We appear to have been successful in rice and field trials are
the next step. We would be pleased to move this into other
crops, such as millet and wheat, where there is a clear
agronomic advantage. Key is identifying the correct promoters to
control the gene expression."
Tester explains that although there is natural variation for the
stelar expression of these HKT1 subfamily of genes in cereals,
which will confer some level of salinity tolerance by
non-transgenic means, the extent of the alterations will always
be limited by the natural variation available.
"This is limited or absent in some species, and could always be
increased, too," says Tester. "So there is likely to be room for
a GM approach in many situations."
Møller, I.S., Gilliham, M., Jha, D., Mayo, G.M., Roy, S.J.,
Coates, J.C., Haseloff, J., and Tester, M. (2009). Shoot Na+
exclusion and increased salinity tolerance engineered by cell
type-specific alteration of Na+ transport in Arabidopsis. Plant
Cell
http://dx.doi.org/10.1105/tpc.108.064568 (Open Access
Paper)
Munns, R. and Tester, M. (2008). Mechanisms of Salinity
Tolerance. Annu. Rev. Plant Biol. 59:651-81.
http://dx.doi.org/10.1146/annurev.arplant.59.032607.092911
For more information, read the Pocket K on Biotechnology with
Salinity for Coping in Problem Soils at
http://www.isaaa.org/kc/inforesources/publications/pocketk/default.html#Pocket_K_No._31.htm
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