UI investigators help trace the origins of photosynthesis

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Sunday, March 18, 2012

How did plants and algae get their ability to turn carbon dioxide and water into sugar and oxygen in the presence of light, a process known as photosynthesis?

It turns out they stole it through an activity called endosymbiosis, according to a landmark study published in the Feb. 17 issue of the journal Science.

Harsha Doddapaneni, study co-author and director of the University of Iowa’s Roy J. Carver Center for Genomics (CCG), says the paper for the first time answers a long-standing question in the evolution of eukaryotes — organisms whose cells have membrane walls and a nucleus. The question: How many primary endosymbioses, or biological thefts, have occurred that gave rise to the plastid, the organelle where photosynthesis takes place in algae and plants?

The answer, garnered from an analysis of the Cyanophora (an algae) genome, is just one. And it occurred more than a billion years ago when a single-celled organism captured and retained a cyanobacterium that itself had once been an independent organism.

According to lead author Debashish Bhattacharya, former UI biology professor currently at Rutgers University, “Analysis of the Cyanophora genome provided conclusive evidence that all plastids trace their origin to a single primary endosymbiosis.” He adds that the genome also tells why the theft is very rare.

“It turns out that the first algae relied not only on the captured cyanobacterium, but also ancient endoparasites, related to modern-day Chlamydiae, that were present in the cells at the time of endosymbiosis. These latter, now silent, partners left dozens of genes in the nuclear genome of algae and plants as footprints of their past existence,” Bhattacharya says.

Highlighting the CCG’s role in the study, Doddapaneni notes that access to “NextGen” sequencing technologies is a fine example of how small genome centers are becoming major players by making important contributions to genome sciences. The CCG provided the 454 sequencing data for the study, and Doddapaneni also participated in the bioinformatic analyses.

The researchers say the study brings scientists one step closer to determining not only what unites all algae as plants, but also what key features make them different from one another and from the genes underlying various functions.

The research was funded by grants from the National Science Foundation. The CCG is a research center in the UI College of Liberal Arts and Sciences Department of Biology.