As Global Warming Accelerates: Israeli Scientists Create Heat-resistant Apricot Trees

Plants can't thrive beyond their naturally optimal range. Now apricots and other crop foods are being manipulated to thrive where they couldn't even grow before.

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Apricot tree (illustration). Apricots generally thrive in cooler climes, but they have a relatively wide range of variants and were a suitable subject to study temperature tolerance, and its manipulation. Picture shows unripe apricot fruits against the backdrop of leaves and the sky.
Apricot tree (illustration)Credit: Fir0002, Wikimedia Commons

The Israeli Air Force is right: when there's doubt, there's no doubt. So, there is no doubt that the world is going to hell at warp speed. August 2016 was the hottest month, not only the hottest August, since Man invented the thermometer, according to NASA. Climate change is bearing down upon us like a freight train and yes, science has spoken. If any questions remain open, they're less whether global warming is real and more how to contend with it and with mass starvation as crops fail.

At Israel's Agricultural Research Organization, better known as the Volcani Institute, they're not waiting for hunger to spread. Israeli scientists have been working for well over a decade on developing crop plants that will not only survive, but thrive, in hotter conditions.

If at first the Volcanites thought about advancing Israeli agriculture, as the state of the planet became clearer, they realized that developing plants to survive in extreme conditions is a planetwide need, Dr. Doron Holland tells Haaretz. And in what could be a breakthrough for global farming, he and his team have identified a genetic mechanism that controls temperature sensitivity in the apricot. With that knowledge, the hope is that heat tolerance in other crop plants can be manipulated.

Gasping in the heat

Like all living and breathing creatures, plants can survive in a range of conditions. But every living and breathing creature, from the ameba to your next-door neighbor, has an optimal range in which they thrive, and beyond which they might survive but do not thrive.

For plants, thriving requires an optimal combination of light and temperature conditions. For fruit trees, the colder the winter, within reason, the better they blossom and the better the quality of their fruit, Holland says.

But timing is key. The tree has to be within the crucial temperature range in the spring: if the right temperature range for flowering arrives earlier (thanks to global warming), in the winter, what will ensue is not flowers and fruit. The tree may survive but will be largely barren. 

Apricot is not native to Israel, and neither are apples, pears or kiwis, though all are now grown here. They did not evolve in the Mediterranean climate and never did grow here optimally, Holland observes, preferring colder winters.

A better apricot

The Volcani institute does not engage in genetic engineering, not least because engineering food crops and transgenic food in general is a regulatory minefield in Israel. The scientists develop better apricots and whatever through a technique whose origin is lost in history: grafting.

With what do they graft said apricot trees? With local plants that are highly heat-tolerant. And, knowing the relevant genetic sequence means the developers don't have to wait for the plant to grow up and start proliferating before they can see if it has the desirable characteristics or not. Once the seed has sprouted, they can sample the plant tissue and determine whether the desired sequence is there.

Doron Holland in an apricot orchard.Credit: Gil Eliahu

Apricots are delicious, but so are strawberries. Why indeed would Volcani work with apricot, a luxury fruit that isn't even native to Israel, rather than a more widely consumed crop? Because apricots are relatively sensitive to changes in environmental conditions. There are also a lot of variants: 150 are grown in Israel alone.

In animals, geneticists have long since located specific genes that code for heat-related receptors (specific proteins embedded in the cell membrane, that receive biochemical signals, causing a reaction inside the cell).  These "thermoreceptors" are responsible for our ability to sense temperature. (Mammals have at least two receptor types, ones that react when the ambient temperature is higher than body temperature, and "cold" receptors that do the opposite.)

In plants, no genes for heat-sensitivity receptors have been identified yet, if there are any, Holland explains. "We did know that plants have a highly accurate gauge for temperature. Even very small differences can affect them intensely." The question is how plants sense temperature and whether that mechanism could be monkeyed with, to make them less vulnerable to heat.

Manipulating to cope

So specific plant heat/cold sensing genes may not have been found. But the Volcani crew did locate an area in the apricot genome that controls how apricot trees cope with changing environmental conditions, including temperature.

In that area, the scientists detected two genes not of receptors, but MADS box type, which affect the plant's tissue differentiation and its reaction to circadian rhythms, as they describe in their seminal 2013 paper in Tree Genetics & Genomes, "ParSOC1, a MADS-box gene closely related to Arabidopsis AGL20/SOC1, is expressed in apricot leaves in a diurnal manner and is linked with chilling requirements for dormancy break".

In short, apricot trees have broad variation in their ParSOC1, wouldn't you know, which turned out to affect their vulnerability to heat stress. "These genes control the plant's need for cold [to thrive], though they do not code for the receptors themselves," Holland clarifies.

Theoretically at least, all or most plants can be expected to have much the same mechanisms. Hence the discovery of a genetic area that controls heat vulnerability is significant for hot-weather agriculture the world wide –even for the Holy Grail of modern human agriculture, wheat.

Mutant peach

Support for their work came from South Carolina, where team had a mutant form of peach that eschewed dormancy break entirely. The trees were not sensitive to the environmental temperature, Holland explains. The mutation turned out to be in the same area that the Israelis had mapped in the apricot.

Later a New Zealand group read the Israeli paper and showed that manipulating the genes the Volcanites had identified changed the cold requirements of kiwi. The fruit, not the bird.

They however were using genetic engineering, Holland says, mucking about with the genome to amplify the expression of the gene. "It's like using a 5-kilo mallet," Holland sniffs. "they caused over-expression of the gene, which is not good. Apparently, changes have to be made much more delicately."

Transgenic or grafted, today we already have more heat-tolerant apricots, peaches, kiwis and even some apples. Holland for one believes this is just the beginning. "We're going to see fruit and vegetables grow where they couldn't grow before," he predicts. Even wheat? Even wheat.