Genetically Modified Potatoes and The Irish Potato Failure

In 1845 blight attacked the potato crop of Ireland. A million people died of starvation and another million or more with enough money to emigrate left for the United States and other countries. The blight knew no borders and never disappeared. It did not cause the famine – the failure of British authorities to divert other food to feed starving farmers caused it.  As readers of Jonathan Swift’s A Modest Proposal may recall, it was not the first time.  For the effects of biological blight and the bizarre, but enduring belief that feeding the starving ruins their souls, read Colum McCann’s novel TransAtlantic.

It may seem prosaic to turn from the chronicles of great writers to the blight itself but science can prevent such disasters.  The plants are destroyed by Phytophthora infestans, which resembles a fungus in that it grows rapidly and produces spores that blow on the wind and spread the disease, but is slightly different. Certain wild strains of potato that are constantly under attack have evolved resistance, but Phytophthora thrives on commercial potatoes in the wet weather of northern Europe and New England.  Today, potato growers apply chemical inhibitors 15-25 times to their potato crops late in the growing season to save them, depending on how many wet days there have been. This practice is expensive, leaves chemicals on the plants and soil and compacts the ground as the sprayers move though the fields.

Plant geneticists at the John Innes Institute in Norfolk, UK have shown that there is another way to avoid the blight. The non-scientist can understand a lot of their paper. Using their knowledge of the circuitry of plant resistance to pathogens, they have transferred several genes that provide resistance in wild potatoes into potato cells growing in a petri dish – in this case cells of a potato variety called Desiree.  Plants cells are astonishing in that they can be broken loose from their cell walls and then grown in a stew of nutrients where they divide indefinitely. In this state, small numbers of genes can be injected into the cells by bacterium called Agrobacterium that has evolved a syringe that transfers DNA to the plant.  When these clusters of transformed cells are put on a jelly like surface and hormones are added, they convert into small plants that produce leaves, stems, flowers, and become normal plants with a few extra protein molecules added to the many thousands of different proteins in the plant cell. Grow them in the soil and they make potatoes.

What did the geneticists do to these plants? The potato plant has hundreds of genes that provide the information to make chemicals that are noxious to invaders – think of nicotine and tobacco. Plants are hugely resourceful if they can mobilize their defenses. When the wind-borne spores of Phytophthora infestans, land on the leaves, the plant has a way to detect them. Special proteins protrude through the membrane of the living plant cells and are shaped to bind to molecules on the surface of the invader. When that happens, a signal is transferred by a series of steps to the genes of the plant and it goes into a defensive mode.  It may thicken its cell wall, produce anti-invader chemicals or kill the infected cells so that the infection does not spread.

The Phytophthora and the Solanum (potato) have been at this battle for millions of years. It is an endless game of serve and return. Sometimes the plant evolves defenses and sometimes the invader overcomes them.  The blight cells outwit the commercial plant by injecting interfering molecules that short circuit the alarm system of the potato plant. (These defenses may have been bred out in the development of the commercial varieties.) It is the botanical equivalent of cyberwarfare and left unchecked, the blight wins, as it did with such terrible consequences in 1845.

Wild potatoes, of which there are many varieties in Peru alone, resist Phytophthora. Recall that the fungus-like blight transfers proteins into the plant cells that silence their alarm system. The wild potatoes are one up on the blight and produce counter proteins that inactivate the Phytophthora proteins so that the natural alarm system of the potato cell functions again. 

Rpi-vnt1.1-transgenic and non-transgenic Desiree in field trials: The genetically modified plants are on the left, the standard are on the right. Rpi stands for Resistance to Phytophthera infestans. Vnt-1 is the name of the gene that provides the instructions for the protein that soaks up the injected Phyophthera toxin.

Jones J D G et al. Phil. Trans. R. Soc. B 2014;369:20130087. The Philosophical Transactions of the Royal Society is an open access journal and has been since the 17th century. 

The scientists in Norfolk identified the genes that produce the proteins that protect wild potato plants.  They transferred them into the commercial variety Desiree. Perhaps they restored a status quo ante. They planted these genetically modified plants next to unmodified plants and waited though a wet summer.  The modified plants lived and produced potatoes and the unmodified ones died. The GMO potatoes could not be distinguished from disease-free normal potatoes. British and European Community regulations require that the new GMO potatoes be immediately burned, but knowing scientists as I do, I bet they found some and ate them. If I had used wild potato genes to protect the food supply, I surely would have eaten them.