In search of the perfect potato

For Jesse Jaynes, genetic engineering involves the quest for the perfect potato. That means giving the potato and other major food plants the nutritional quality of meat.

As the Louisiana State University biochemist explained in a telephone interview, he and his colleagues have already come a long way toward that goal. In the process, he has found a possible way to help these food plants resist the attacks of bacteria and fungi. It involves a small protein that may also be useful in medicine.

To appreciate what Dr. Jaynes is up to, recall that proteins are made up of building blocks called amino acids. Eight of these acids are essential for a balanced human diet. Meat protein has a good mix of all eight acids. But plant protein generally lacks one or more of them. So billions of people who rely mainly on the major food plants - potato, cassava, and the cereal grains - are chronically ill- fed.

We asked Jaynes how he hopes to help these people eat better:

Do you really expect to produce a potato with the protein value of meat?

Yes. That's right. I think it's possible. And that is the goal.

I've made calculations ... [for] a child ... about eight years old, 10 years old or whatever. Their daily essential amino acid requirement is the same as mine ... When I first made that calculation five or six years ago, it really hit me how important a source of essential amino acids is ... for a young growing person to have.

So I synthesized these genes ... that, theoretically, could [make potatoes such a source]. The genes that I synthesized encode proteins that are much better than beef as far as the essential amino-acid content goes.

Why work with potatoes?

I chose the potato because, at the time, potato was the most important crop that one could genetically engineer. That was in '83, '82. The technology has moved since then to where we can, perhaps, genetically engineer cereals. But the search for the perfect potato would be [to engineer] one which a person could eat and obtain their total essential amino-acid requirement.

That's been my goal since about '82. And we've, of course, moved into other areas and other plants. Cassava is another plant which perhaps 2 billion people in the world rely on. And it's a very poor source of protein. So this persistent malnutrition that one sees due to the lack of high-quality protein is also found in those people that eat cassava, those people that eat rice or maize or whatever.

So my initial genetic engineering work came about trying to do something about that. And, in collaboration with John Dodds [of the International Potato Center in Lima, Peru], we have genetically engineered potatoes that are producing this [better] protein. But we find out that it's not producing enough of it to really achieve what we wanted. So we're climbing another mountain, now, trying to get high amounts of this protein produced. And I'm very optimistic that we will.

It may take another four or five years. But we will have plants including potatoes, cassava, and rice - those are the three that we're focusing on - that are going to be more nutritious and, hopefully, prevent the protein malnutrition that one sees.

People need a mix of eight amino acids - isoleucine, leucine, valine, threonine, tryptophan, lysine, methionine, and phenylalamine. Which ones are you working with?

I've analyzed the amino acid content in crops and the five most deficient are isoleucine, threonine, methionine, tryptophan, and lysine. My first gene focused on those. The protein that's produced by that gene has 23 percent lysine, 12 percent methionine, and 6 percent tryptophan and threonine and isoleucine. And that's the one that's being expressed in potato and cassava right now....

We've found a very interesting compound which appears to have some potential in [plant and human] disease [control]. And, in trying to understand how this compound worked, I designed a new protein which I think will be much better for the nutritional amino acids than the first one.

How did you find it?

Probably 40 percent of the world's crops are lost to the [bacterial and fungal] diseases. And in another part of my research, I came across some early papers that talked about how insects protect themselves from disease. So I synthesized a gene for a small protein which, according to these people, kills bacteria. And so my original goal in '85 was to put that gene into plants to make them more bacterial disease resistant.

And that work's going on. But in the process, I synthesized some of this compound and found that it not only killed bacteria, but it killed malaria pathogen and [and other disease related microbes and even cancer cells]. ... And [it] wouldn't harm normal cells - mammalian cells....

I think the potential for providing increased [plant] disease resistance will go a long way in helping the developing world. ... And we might have a new chemotherapeutic [medical] agent....

Will this research really fulfill such ambitious promise?

I'm very optimistic. I really think that biotechnology and genetic engineering can do some great things to help people in the developing world. I know a lot of people talk about all the great things that are going to happen here [in the United States]. And certainly we will be beneficiaries of that. But I think, overall the prospects for improving the lot of those people are much brighter [now] in the developing world through this technology.