CO₂ is used in photosynthesis in plants to manufacture sugars required for plant growth. As a response to limiting concentrations of CO₂ in the atmosphere, some plants have evolved mechanisms to capture and concentrate the CO₂ in their cells to improve photosynthetic efficiency and increase growth.

This is a real breakthrough. No one had previously identified any of the proteins that are involved in transporting CO₂ in microalgae.

—Martin Spalding, professor and chair of the department of genetics, development and cell biology, Iowa State University

The main protein that Spalding and his team have identified that is responsible for transporting CO₂ is called HLA3.

The research by Spalding; Deqiang Duanmu, a graduate student in Spalding's department; and Amy Miller, Kempton Horken and Donald Weeks, all from the University of Nebraska, Lincoln; is published in the current issue of the journal Proceedings of the National Academy of Sciences.

Now that the HLA3 protein has been identified, Spalding believes there are several possibilities to use the gene that encodes this protein. The recent surge in interest in using microalgae for production of biofuels raises the possibility of increasing photosynthesis and productivity in microalgae by increasing expression of HLA3 or other components of the CO₂ concentrating mechanism, according to Spalding.

Since all plants need CO₂ to thrive, introducing the HLA3 gene into plants that do not have the ability to concentrate CO₂, could help those plants grow more rapidly. Spalding says several plants would be candidates for the HLA3 protein.

One of the things we’ve been working on is the prospect that we may be able to take components of the CO₂ concentrating mechanism for microalgae, such as this HLA3, and put it into something like rice and improve photosynthesis for rice.

—Martin Spalding

Rice and other commodity crops such as wheat and soybeans do not have any CO₂ concentrating mechanism.

Resources

• Deqiang Duanmu, Amy R. Miller, Kempton M. Horken, Donald P. Weeks, and Martin H. Spalding (2009) Knockdown of limiting-CO₂–induced gene HLA3 decreases HCO₃^- transport and photosynthetic Ci affinity in Chlamydomonas reinhardtii. PNAS 106:5990-5995 doi: 10.1073/pnas.0812885106