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After 13 years, a global team conquers the ‘Mt. Everest of plant genomics’

The wheat genome has finally been mapped in sufficient detail to enable more rapid and robust genetic tinkering — perhaps on a track that could head off mass starvation in coming decades.

Wheat’s current stature is the somewhat unnatural consequence of hybridization and other meddling by humans that goes back millennia, but made a quantum leap with the so-called “Green Revolution” of the 1950s and 1960s.
REUTERS/Kai Pfaffenbach

Care to test yourself with a little quiz concerning four of the world’s most important staple crops? Great!

Thinking now of corn, rice, wheat and soybeans:

  1. Which of these occupies the most cropland worldwide?
  2. Which accounts for the largest volume in world trade, as measured by monetary value?
  3. Which is a critical food source for one person out of three worldwide?
  4. Which provides us earthlings with more protein than any other vegetable source — more protein, in fact, than we get by eating meat?
  5. Which lacks a genetically modified version?

If I were just taking this quiz instead of having written it, I’d probably answer corn, corn, rice, soy and … gee, No. 5 looks like a trick question, so I’ll say … “none of the above”?

Give me a zero. The correct answers are: wheat, wheat, wheat, wheat and wheat.

Which goes a long way to explaining the excitement over last week’s announcement that the International Wheat Genome Sequencing Consortium (IWGSC) has finally mapped wheat’s genes in sufficient detail to enable more rapid and robust genetic tinkering — perhaps on a track that could head off mass starvation in coming decades.

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Why do we need more wheat?

Wait, wait, you may be saying — if wheat is already leading the league in so many ways, why does it need any tinkering?  Four reasons:

First, wheat’s current stature is the somewhat unnatural consequence of hybridization and other meddling by humans that goes back millennia, but made a quantum leap with the so-called “Green Revolution” of the 1950s and 1960s. Research-driven improvements in growing methods — and important new hybrids, like Japanese dwarf varieties that produce more grain on a shorter stalk, and stand up better to toppling forces — have boosted world production by 300 percent in not quite 60 years.

Second, the world population is projected to swell from around 7.6 billion people now to about 9.6 billion people in the 32 years from now to mid-century. The IWGSC calculates that feeding those extra mouths will require yields to increase by 1.6 percent per year, every year.

Third, wheat production in recent years has been falling in some parts of the world, and stagnating globally, because of the usual array of pests, disease and bad weather, now complicated by climatic shifts toward hotter, drier conditions as the globe continues to warm.

Fourth, the answer can’t be found in simply planting more acreage. To quote the consortium’s announcement, “In order to preserve biodiversity, water, and nutrient resources, the majority of this increase has to be achieved via crop and trait improvement on land currently cultivated, rather than committing new land to cultivation.”

Thus the effort to form the IWGSC, whose code-cracking team includes 200 scientists scattered across 73 institutions and 20 countries, and launch it on a crash program to do for wheat what had been done for rice in 2002, for soybeans in 2008, and for maize (corn) a year after that. (Not to mention humans, for whom a full genetic map was published back in 2000.)

Distributing the work so widely meant it could be snipped into independent projects and scattered among the teams, allowing them to work independently and coordinate their results at the end.

‘Mt. Everest of plant genomics’

Still, it took them 13 years to conquer what was widely described as “the Mt. Everest of plant genomics,” by completing a task more than a few experts had called impossible.

The wheat variety studied by the IWGSC team is called Chinese Spring, an ordinary bread flour of the cultivated species Triticum aestivum; it is probably the most widely grown version of that species in the world.  Like all wheat, it’s a grass, and it looks pretty simple because that’s how most of us tend to see grass.

However, its genetic material is quite complex compared to, say, rice’s, with a genome about one-fortieth the size of Chinese Spring’s. Or, for that matter, compared to yours.

Chinese Spring has but 21 chromosomes, which of course is less than the 23 of you and me. On the other hand, our 23 chromosomes have something like 20,000 to 25,000 individual genes. In turn, these are built from around 3 billion base pairs of the fundamental compounds that form DNA (Guanine bonded to Cytosine, Adenine bonded to Tyrosine).

Chinese Spring’s chromosomes contain more than four times as many individual genes (107,891, says the IWGSC). Also, more than five times as many base pairs (north of 16 billion).

As always happens with genetic sequencing, a lot of those genes were discovered to be nonfunctioning relics or duplicates or otherwise unnecessary debris. But the garbage makes the mapping harder, not easier, when your aim is not only to map the genes’ locations but also to annotate their functions, by sampling the code in different seasons, at different life-cycle stages, while subject to a variety of environmental conditions, and so on.

A further complication: The 21 chromosomes of the Chinese Spring genome are distributed among three “sub-genomes” of seven chromosomes each, a relic of wheat’s history of evolution and interbreeding with other grasses, sometimes assisted by the humans who have been cultivating it for more than 10,000 years. (It amuses me, chomping on my Stoned Wheat Thin, to reflect on the DNA of ancient, wild “goat grasses” preserved there.)

Weirder still: Your human genome, as with most mammals, is in a diploid arrangement — two sets of those 23 chromosomes, one from Mom and one from Dad. Some wheat species are diploid, too, including the “ancient grain” einkorn; among the first be cultivated, it persists in both wild and domesticated forms. But then you have your tetraploids, with four sets — durum, emmer, Khorasan. And finally your hexaploids, with six sets, including spelt and most bread wheat, like Chinese Spring.

The potential of modification

Now that the wheat genome has been mapped, the expectation is that scientists will begin to make modifications at the molecular level to increase pest resistance and drought tolerance, to shift flowering times away from adverse conditions, to improve nutritional value (though wheat is an important source of protein, as well as vitamins and minerals, some dream of adding amino acids it now lacks) … the sky seems to be the limit as researchers outline the promise of higher yields and improved food quality.

Catherine Feuillet of  Inari Agriculture, an American member of the IWGSC team, seemed to speak for many when she said:

I’d wish I’d be at the beginning of my career again because the fun is really starting now and we can efficiently decipher the biology of our favorite crop. Having this sequence and combining it with other advances in science and technologies is fundamental to enable us understanding how wheat plants perform in their environments and boost our ability to improve wheat production worldwide.

But there are other maps to be drawn for wheat beyond its genetic sequence, and they will have to trace pathways from the laboratory through difficult territories of policymaking, regulation, markets and agribusiness.

Resistance to GMO crops remains high in many parts of the world, including some where hunger is a serious, present danger. Wheat has been undergoing off-and-on efforts at genetic modification for more than a decade, based on an earlier and less detailed sequence than the once announced last week; Wired magazine reports that Monsanto scientists worked for a while on a Roundup-ready version before concluding that the world (meaning the marketplace) wasn’t ready for it.

And you need look no further than Golden Rice to see that even a food staple modified to enhance public health — in this case, through internal production of beta carotene aimed at easing vitamin A deficiencies  — isn’t necessarily going to find favor.

Fourteen years after its first field trials, 13 years after a second version was developed, Golden Rice has only just won approval for cultivation in the U.S. and Canada, along with Australia and New Zealand. Whether, when and where it may actually begin to deliver its promised benefits is impossible to predict.