September 2008 - Issue #3
Biology probed for the secrets of crop survival
Story by Dr Whitney Macdonald
View articles in related topics: Molecular Science, Horticulture
While farmers the world over have been struggling under the withering impact of a drying climate, new research is helping scientists crack the genetic code of a family of proteins that could help Australia - the world's driest inhabited continent - continue to see its wheat industry flourish.
The research has a potential role in securing an industry worth more than $6 billion a year to the national economy, plus contributing to global efforts to protect cereal crops against drought, climate change and deteriorating soils.
By identifying DNA 'bio-codes' responsible for stress tolerance in wheat, Swinburne University of Technology researchers are working to better understand how cereal responds to stress, and in time feed this knowledge into breeding programs so that crops are better able to cope with prolonged hot, dry weather.
"If we can find lines of crop that naturally possess the genetic make-up to withstand the effects of salinity ... they could eventually be used in a breeding program to make wheat crops more robust."
Dr Mrinal Bhave
Molecular biologists at Swinburne are characterising DNA and protein sequences in wheat, targeting a gene family thought to play an important role in how wheat responds to environmental stresses, including drought and salinity.
Kerrie Forrest, a PhD student working under the supervision of Dr Mrinal Bhave in the Faculty of Life and Social Sciences, is investigating the genes that encode proteins of the aquaporin family in bread wheats. Aquaporins are proteins that form specific channels involved in transporting water through the cell membrane, and are critical for cell function and regulation.
Present in all forms of life, aquaporins were first discovered in humans about nine years ago by Professor Peter Agre, a discovery that earned him the 2003 Nobel Prize in Chemistry.
In plants, aquaporins are involved in regulating any process requiring the plant to take in water. Dr Bhave has been studying aquaporins since 2004 and says that research into stress responses in plants has become a widespread area of interest.
"There are a range of genes in plants that are now known to be involved in salinity and drought tolerance. Aquaporins are emerging as key players since they are the gatekeepers for the channels through which water travels in the cell."
Supported by a scholarship from the Grains Research and Development Corporation - an organisation that invests in R&D to help grain growers - Ms Forrest's PhD project involves systematically trying to clone and identify all wheat aquaporins.
Ms Forrest says that this gene family has been studied in other plants, including rice and maize, but has yet to be fully characterised in wheat. "We knew that aquaporin genes were implicated in drought and salinity responses in other plants," she says. "Though we suspected that aquaporin genes would also be involved in stress response in wheat, we didn't know how large the aquaporin gene family was, which genes were important, or how they functioned."
Using bioinformatics tools the scientists are able to compare the sequences that they identify in wheat aquaporins with sequences that others have characterised in wheat, rice, and other plants, allowing them to determine if they have identified new genes.
Within a cell, DNA is packaged into structures of varying lengths called chromosomes. In contrast to the two sets of chromosomes that classify humans as diploids - inheriting one set from each parent - bread and durum wheat species are polyploids, meaning wheat has more than two sets of chromosomes. These species of wheat typically have between four and six sets of chromosomes, which make studying wheat genetics complicated.
To isolate the genes responsible for encoding aquaporins in wheat, Ms Forrest uses a technique called polymerase chain reaction - a powerful molecular biology tool that allows a scientist to produce millions of copies of DNA from a gene of interest, so that the sequence of the DNA can be characterised and used in further functional gene studies.
Of the 35 genes that Ms Forrest has identified in the wheat aquaporin family, she has tested four for their response to salt stress, by monitoring whether the genes were 'turned on' or 'off' when cells were exposed to equivalent levels of salinity found in agricultural regions.
"Aquaporins have a role in the response of wheat to salinity. My results showed that when wheat is exposed to high salt concentrations, two of the studied genes were turned on, while the other two genes were turned off."
Dr Bhave says that salinity problems in Australia stem from the continent's origins and the types of crops planted since early European settlement. "Modern agricultural practices have brought salt to the surface of the soil resulting in loss of agricultural land. If we can find lines of crop that naturally possess the genetic make-up to withstand the effects of salinity we would like to work with those in the hope that they could eventually be used in a breeding program to make wheat crops more robust." This strategy would exploit the natural genetic variation to breed strains of wheat that show superior drought and salinity tolerance.
Though Ms Forrest's PhD work is coming to an end, the research is still considered in the early phase of the project. Dr Bhave will supervise two new PhD students who will continue to investigate the effects of drought on the genes identified in wheat. Her colleague Dr Tony Barton will also be involved in their supervision.
"Once we know how many different wheat genes there are, and which ones are likely to be more important for salinity and drought tolerance, we want to compare many different kinds of wheat samples sourced from all over the world and expose them to drought conditions, varying amounts of humidity, temperature, and salinity," Dr Bhave says. "We then hope to identify the most sensitive and tolerant genotypes and compare them to see how these genes behave in the sensitive and tolerant plants."
