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Back from the Dead

Genetically modified chickpea plants

Genetically modified chickpea plants that express a pro-survival gene derived from Australian resurrection plants (Tripogon loliiformis) are more stress-tolerant. This image shows non-GM (left) and GM (right) chickpea plants that had been drought-stressed at flowering by applying half volumes of water for 30 days. This photo was captured after an additional 35 days without watering.

By Brett Williams & Sagadevan Mundree

Resurrection plants can survive for years in an air-dry state before growing at full capacity when the rain comes. How do they do it, and can this trait be transferred to improve the tolerance of crops to drought, heat, salinity and infection?

Plants require significant amounts of water. On a hot, sunny day some plants replace every water molecule in their body within an hour.

We make cars more fuel-efficient to reduce costs and emissions. Can we make plants more water efficient to save water and get more crop per drop?

Plants can contain as much as 90% water. In contrast, humans contain approximately 60% water. To put the water demands of plants into perspective, if a crop plant loses water to levels equivalent to humans then it will wilt and die.

How Do We Help Plants Tolerate Drought?

A small group of flowering plants can lose up to 90% of their water and remain in that state for months. These “resurrection plants” may hold the secret to improving drought tolerance in crops.

Like the phoenix, resurrection plants are able to dry to an air-dry “ash” state and, upon watering, are “rejuvenated” to start growing at full capacity within 24–72 hours.

Imagine if we could generate crops that can tolerate significant water loss during droughts and then start to grow again when the rains come.

Recently our group found that the cells of an Australian resurrection plant do not die upon drying. Upon watering, existing tissue recovered rather than new fresh tissue generating.

Further research has shown that the cells can survive from months to years when in the dry state. Resurrection plants have even been found “thawed” out and growing after spending hundreds of years frozen in Antarctic ice caps that are beginning to melt due to global warming.

How do the cells in resurrection plants survive in such harsh conditions? The observation that cells remain alive in resurrection plants when dried has led us to look at the different strategies that plants and animals use to suppress cell death. The details of these analyses have recently been published in PLoS Genetics (http://tinyurl.com/htlsxsw).

What we found is that the resurrection plant increases the amount of trehalose, a type of sugar that most land plants do not accumulate to great levels. The resurrection plant uses this sugar to regulate programmed cell death pathways.

Programmed cell death is a process that occurs in all organisms. This process decides whether a given cell lives or dies. This occurs during development as well as in response to stress.

In humans, programmed cell death helps the formation of our fingers and toes by telling the cells between our fingers to die while surrounding cells divide and grow to form our digits.

It is thought that programmed cell death helps the organism survive by sacrificing a few cells in a controlled manner that restricts the number of cells from dying uncontrollably.

Since all stresses eventually lead to death, if we can control the decision of programmed cell death pathways it may be possible to generate crops that are tolerant to a range of stresses such as drought, heat, salinity and infections by fungi and other pathogens.

Armed with this new information, can we transfer the survival traits of a resurrection plant to crops?

Feeding a Growing Population

The global human population is currently at approximately 7.5 billion, and is expected to peak at 10 billion in the mid-2050s. To feed this population we must produce the same amount of food in the next 50 years than was produced in the past 10,000 years combined. This equates to almost a 70% increase in agricultural production.

Can we increase our food supplies to meet this demand without devastating the planet?

Although agriculture utilises almost 70% of our global freshwater sources, it takes about 100 times less water to produce 1 kg of plant than animal-based protein. This is because animals need both water directly as well as plants as food. Thus, water required for the production of an animal’s plant-based food must be included as part of the water requirements needed to produce animal protein.

Can we survive on plant-based proteins alone? High-protein plants such as legumes and pulses may provide the answer.

Legumes are plants that produce fruit enclosed in pods. Pulses are legumes, but the pulse refers to the dried seed of the legume. Pulses such as chickpeas, mungbeans, lentils and faba beans are some of the most nutritious foods available and are high in protein, fibre and essential minerals such as iron, folate and other B-group vitamins.

Like all crops, pulses are susceptible to drought and other environmental stresses. Can we improve the stress tolerance of pulses?

Using our observations that trehalose accumulation induces survival pathways, we have transferred a single gene from a survival pathway of an Australian resurrection plant into chickpeas and assessed the plants for stress tolerance. Early glasshouse trials have demonstrated that the genetically modified chickpeas are drought, salinity and heat-tolerant, as well as resistant to the grey mould fungus Botrytis cinerea found on strawberries left for a few days outside of the fridge.

The genetically modified chickpeas are also producing larger quantities of higher quality, larger fruit.

Although at the early stages, these experiments demonstrate great potential for the transfer of stress resistance from resurrection plants into crops without affecting growth rates or yields.

In the future, using newly developed gene editing techniques it may be possible to develop non-GM stress-tolerant crops that can continue to yield even in dry environments.


Brett Williams is Vice Chancellor’s Research Fellow and Sagadevan Mundree is Director of the Centre for Tropical Crops and Biocommodities at Queensland University of Technology.