By Diana Yates
University of Illinois researchers have built a better plant, one that
produces more leaves and fruit without needing extra fertilizer. The
researchers accomplished the feat using a computer model that mimics the
process of evolution. Theirs is the first model to simulate every step of
the photosynthetic process.
Photosynthesis converts light energy into chemical energy in plants,
algae, phytoplankton and some species of bacteria and archaea.
Photosynthesis in plants involves an elaborate array of chemical reactions
requiring dozens of protein enzymes and other chemical components. Most
photosynthesis occurs in a plant?s leaves.

?The question we wanted to ask, was, ?Can we do better than the plant,
in terms of productivity?? ? said principal investigator Steve Long, a
professor of plant biology and crop sciences at the University of Illinois.

It wasn?t feasible to tackle this question with experiments on actual
plants, Long said. With more than 100 proteins involved in photosynthesis,
testing one protein at a time would require an enormous investment of time
and money.

?But now that we have the photosynthetic process ?in silico,? we can
test all possible permutations on the supercomputer,? he said.

The researchers first had to build a reliable model of photosynthesis,
one that would accurately mimic the photosynthetic response to changes in
the environment. This formidable task relied on the computational resources
available at the National Center for Supercomputing Applications.

Xin-Guang Zhu, a research scientist at the center and in plant
biology, worked with Long and Eric de Sturler, formerly a specialist in
computational mathematics in computer sciences at Illinois, to realize this
model.

?The question we wanted to ask, was, ?Can we do better than the plant,
in terms of productivity?? ? said principal investigator Steve Long, a
professor of plant biology and crop sciences at Illinois.

After determining the relative abundance of each of the proteins
involved in photosynthesis, the researchers created a series of linked
differential equations, each mimicking a single photosynthetic step. The
team tested and adjusted the model until it successfully predicted the
outcome of experiments conducted on real leaves, including their dynamic
response to environmental variation.

The researchers then programmed the model to randomly alter levels of
individual enzymes in the photosynthetic process.

Before a crop plant, like wheat, produces grain, most of the nitrogen
it takes in goes into the photosynthetic proteins of its leaves. Knowing
that it was undesirable to add more nitrogen to the plants, Long said, the
researchers asked a simple question: ?Can we do a better job than the plant
in the way this fixed amount of nitrogen is invested in the different
photosynthetic proteins??

Using ?evolutionary algorithms,? which mimic evolution by selecting
for desirable traits, the model hunted for enzymes that ? if increased ?
would enhance plant productivity. If higher concentrations of an enzyme
relative to others improved photosynthetic efficiency, the model used the
results of that experiment as a parent for the next generation of tests.

This process identified several proteins that could, if present in
higher concentrations relative to others, greatly enhance the productivity
of the plant. The new findings are consistent with results from other
researchers, who found that increases in one of these proteins in transgenic
plants increased productivity.

?By rearranging the investment of nitrogen, we could almost double
efficiency,? Long said.

An obvious question that stems from the research is why plant
productivity can be increased so much, Long said. Why haven?t plants already
evolved to be as efficient as possible?

?The answer may lie in the fact that evolution selects for survival
and fecundity, while we were selecting for increased productivity,? he said.
The changes suggested in the model might undermine the survival of a plant
living in the wild, he said, ?but our analyses suggest they will be viable
in the farmer?s field.?

Long also is the deputy director of the Energy Biosciences Institute
and an affiliate of the Institute for Genomic Biology and the supercomputing
center.

Source: University of Illinois
www.news.uiuc.edu/news/07/1109photosynthesis.html