In 2008, Jeff Chen caused a stir in the world of plant biology when he identified a key mechanism of “hybrid vigor” in the common experimental plant, Arabidopsis.
Now, thanks to a $2.5 million grant from the National Science Foundation, he and his colleagues are expanding their investigation of hybrid vigor to corn, which is the biggest crop in the United States. Advances in understanding hybrid vigor in corn could lead to big increases in yield.
The phenomenon of hybrid vigor was first systematically described by Charles Darwin in 1876, after he noticed that his toadflax plants that were the product of cross-fertilization between distinct toadflax parents were “plainly taller and more vigorous” than those that were self-fertilized clones of their parents.
Since Darwin’s time scientists have observed hybrid vigor, and farmers and breeders have exploited it, in a wide range of species.
Hybrid plants such as hybrid corn are larger and have more biomass and bigger seeds than their parents. Mutts tend to be healthier than pure bred dogs. Even in humans there’s (controversial) evidence of hybrid vigor.
The mechanisms that lead to hybrid vigor are not completely clear. Chen answered one part of the question in 2008. It has to do with the hybrid plants’ internal clocks. Their circadian clock regulators respond to daylight by ramping up the expression of certain genes, while repressing the expression of other genes, in ways that are very different from their inbred parents.
As a result the hybrids and polyploids (plants with two or more sets of chromosomes) show increased photosynthesis, higher amounts of chlorophyll, and greater starch accumulation than their parents. This means bigger plants.
With the new NSF grant, Chen and his colleagues at UC Berkeley want to know if a similar or different mechanism is at work in corn. The approach will be similar to what he and his team did with Arabidopsis. They’ll take samples from the hybrid and inbred corn every three hours, around the clock, and look at the genes being expressed and compare that to the metabolic and protein levels. They’ll also study the functions of key regulatory genes in transgenic plants that overexpress these genes. This will allow them to examine if the clock regulates metabolic vigor or the metabolites regulate the clock.
Chen is confident they’ll make progress in identifying the mechanisms underlying hybrid vigor in corn. The more exciting prospect is that he and his colleagues will be able to use their knowledge to predict and select which parent plants are likely to produce more vigorous hybrid offspring. If they can succeed in this, they may have something very valuable to offer to big agribusiness.
“The big ag companies are all looking for this,” he said, “a way to predict what pair of parents will produce better hybrids. They know genetic diversity is important, and they experiment with it intensively, but it’s crude. We’re hoping to enable them to become much more precise.”
Chen and his team will also use the money to train undergraduate students in the UTeach program. Many of these students will become K-12 teachers in mathematics, science, and computer science. Hands-on experience with genomics and biotechnology will broaden their knowledge base to improve STEM education for future scientists, engineers, lawyers, and politicians.