Moroney Lab

My area of research is the CO2 concentrating mechanisms (CCM) of algae. This CCM is a way photosynthetic organisms concentrateCO2 at the site of Rubisco increasing photosynthetic efficiency. Rubisco is a very slow enzyme with a low affinity for CO2. Current atmospheric levels of CO2 are less than optimal for Rubisco, so, if the CO2 level in a plant can be increased there is usually an enhancement of photosynthesis. The CCM is very common in nature, with almost all aquatic organisms (algae and photosynthetic bacteria) having some variation of the mechanism. It is estimated that about 50% of the photosynthesis that takes place on Earth is done by organisms employing a CCM, so it is a very important biological pathway. A well supported model for how the CCM in cyanobacteria works has been developed (Figure 1) however, the CCM is not completely characterized in eukaryotic algae. I have chosen to concentrate on theCCM of Chlamydomonas reinhardtii, a unicellular green algae that has been used as a model organism for many years.

Figure 1

In earlier studies, my laboratory has taken advantage of the fact that theCCM is inducible in C. reinhardtii being present only in cells grown on limiting CO2. My laboratory has used the methods of protein isolation and molecular biology to characterize proteins and genes induced by low CO2. By identifying induced genes and proteins, we have characterized a number of genes encoding carbonic anhydrases, putative bicarbonate transporters and components of the photorespiratory cycle.

In 2007, the genome of C. reinhardtii was published. We have used this information and have taken advantage of new techniques that allow us to transform C. reinhardtii with genes that confer antibiotic resistance. A few years ago we initiated an insertional mutagenesis study of the CCM. We have generated and screened 42,000 insertional mutants that could not grow well on low CO2 concentrations. The assumption is that these mutants are defective in a component of theCO2 concentrating mechanism or the photorespiratory cycle. We have identified many mutants from this screen and have been physiologically characterizing these mutants using a combination of genetic complementation, reverse molecular genetics and inverse PCR.

From these studies we have found nine carbonic anhydrase genes and a number of candidate genes that might encode bicarbonate transporters. We have put together a working model of how the CCM works in C. reinhardtii (Figure 2). Currently we are working to localize each carbonic anhydrase within the cells and determine which ones are important in the CCM. We are also working to determine which transporters are actually carrying bicarbonate and whether they are essential to the functioning of the CCM.

Figure 2