Evolution of C4 plants

Author:  Liebers Kate

Date:  January 2008

The evolution of C4 plants – which include maize, sugar cane, and other biofuels - has been of great ecological and agricultural importance. However, the origin of C4 plants from C3 plants, has only been a speculation until now.

The difference between C3 and C4 plants lies in their photosynthetic pathways in which CO2 is fixed into a three- or four-carbon compound, hence the name "C3" and "C4" plants, respectively.

When CO2 is limited in the plant cells (which occurs under high temperature, drought, salinity and low CO2 atmosphere), O2 is used by the plant, a process named photorespiration, which represents a waste of energy for the plant. This is what happens in the C3 plants where enzyme that fixes atmospheric CO2 also has an affinity for O2. In C4 plants, however, atmospheric CO2 is fixed by an enzyme that has no affinity for O2, disabling the wasteful photorespiration.

Pascal-Antoine Christin and colleagues from the University of Lausanne, Switzerland study the importance of "one of the most successful ecological and evolutionary innovations in plant history" and try to trace the age of the various C4 lineages which will reveal the genetic mechanisms linked to the evolutionary history.

Constructing phylogenetic trees to represent genetic relationships between various species of grasses, and using Bayesian molecular dating to estimate the ages of the 17-18 independent C4 plant lineages, the study revealed the importance of CO2 decline that occurred millions of years ago on the evolution of C4 plants.

Furthermore, the study raised questions of how these plants could be affected by current climate changes that influence CO2.

"Yes, it is likely that some plants become extinct due to global changes," Christin said. "However, the exact nature of these changes and their impacts cannot be guessed without further and more extensive studies."

Written by Kate Liebers

Reviewed by Jeffrey Kost, Pooja Ghatalia

Published by Pooja Ghatalia.