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ScienceWise - Nov/Dec 2009

Drought Resistant Wheat

Article Illustration
Lisa Chew, Nok Pornsiriwong and Gonzalo Estavillo in the plant growth room. Lisa is working as a technician on a GRDC-funded project to isolate SAL1 mutants in wheat using molecular techniques. Nok’s PhD project deals with the basic understanding of how SAL1 gene is involved in water movement across the plant.

Helping to Protect Australia’s Food Supply Against Climate Change

As climate change begins to tighten its grip on the world, many regions including Australia, are starting to experience increasingly erratic weather patterns. Most climate models predict that the vast wheat growing areas of Southern Australia will become significantly dryer over the next fifty years with serious economic implications. The 2002-03 drought resulted in a 20% reduction in agricultural income, which in turn resulted in 1.6% drop in GDP! Consequently anything that may help food crops like wheat survive dry periods has got to be a very good thing for Australia.

A group of plant scientists from Thailand, Argentina and Australia now at The Australian National University, have been studying a subtle mutation in Arabidopsis (a small, rapid growing plant) that may have important implications for drought resistance throughout the plant kingdom. The group is lead by Dr Gonzalo Estavillo and Professor Barry Pogson.

“This work actually began purely by chance when we were looking at different mutant varieties of Arabidopsis that had unusual responses to high light. We discovered a particular mutant, sal1, that survived longer than the normal plant under water deficit conditions, and seeing the obvious potential, we began to investigate.” Dr Estavillo says.

The sal1 mutant lacks just one protein, SAL1. Although the exact function of SAL1 is still debated, it’s known to be important to the physiology and biochemistry of plants. The group have been studying where the protein is located in the cell, its role in intracellular signalling and in regulating the amount of water that travels through the plant. Their aim is to better understand the exact function of SAL1 and why its absence should improve a plants ability to withstand drought.

“We’re really impressed by how many processes depend on SAL1. For example, the regulation of the amount of water in the plant is governed by SAL1. The pool of plant-made chemicals (or metabolites) is also greatly affected in the plants lacking the SAL1 protein and the functioning of many different genes is altered. Similarly, the amounts of several key regulatory players in signals that control plant development and responses to drought are different in the sal1 mutant.”

Because of its relatively well-understood genome and rapid growth, Arabidopsis is a “model” plant used by many biologists to study the interplay of genes with plant physiology.  But in order to realise the great practical benefits of drought tolerance, the mutation must of course, occur in a food crop such as rice or wheat.

If additional new genes were required to achieve drought tolerance in a plant like wheat, then scientists might splice the new gene into the existing genome. But this would come with the burden of extensive safety testing and also incur public concern about GM food stock. However, because the basis of this particular mutation is a missing gene not an added one, it’s possible to achieve the benefits without genetic modification; rather it can be achieved by traditional plant breeding techniques. This means that such mutant plants could potentially be introduced to commercial varieties very quickly.

One of the obstacles in finding a similarly impaired SAL1 gene in wheat is that wheat has been interbred and cross cultivated for over six thousand years, resulting in a highly complex genome. To make matters worse, wheat carries between two and four copies of its DNA in each cell depending on the variety. Consequently, the scientists may have to find several different wheat lines that lack the different SAL1 genes in order to reach their goal of improved drought tolerance in wheat.

“The ultimate aim of this project is to develop wheat lines with improved drought tolerance and water use. The next step will be to identify wheat mutant plants lacking SAL1 genes identified by molecular biology procedures. We expect that these mutants should remain green, turgid and photosynthetically active, producing more leaves, flowers and seeds during mild to moderate water deficit.”

If all goes according to plan, the researchers will begin to introduce these mutant characteristics into the elite wheat cultivars currently used in agriculture.

But it’s not just crop production that looks set to benefit by this research. It may also be an important step in unravelling the function and mode of operation of different plant genes. The researchers are looking at what happens when they cross the drought resistant sal1 mutant with another mutant strain known as open stomata 1. Plants carrying the open stomata 1 mutation are unable to sense the plant hormone Abscisic Acid (ABA) released during stress. As a result, they fail to close their stomata to restrict water loss during drought and perish rapidly in dry conditions. However, when crossed with the sal1 mutant, the progeny have renewed drought tolerance. The researchers believe that studying the interplay of these two mutations may lead to vital clues about the complex action of ABA and the genes that control it.

Most breakthroughs in science come from multiple researchers and institutions working collaboratively and this SAL1 research is no exception.

“Our group is part of the Australian Research Council (ARC) Centre of excellence for Plant Energy Biology along with the University of Western Australia and the University of Sydney. We are also collaborating with Dr Crispin Howitt and other scientists at CSIRO Plant Industry and have received funding from the Grains Research Development Council for the wheat project. This brings together a wide range of complementary facilities and expertise and makes this project really exciting to work on.”

The value of the Plant Energy Biology Centre and the ground-breaking work it performs was clearly reflected by a recent ARC decision to expand and extend the centres funding until 2013.

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