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Red and green algae: Separated at birth

RUTGERS (US) — They may live separate lives now, but a new study finds that red and green algae come from a common genetic ancestor, sharing about half the genes in their genome.

Scientists had long thought this must be so, but had little evidence to back up their hunch, because red algae genomes are usually very large, and their sequencing is a long, involved, expensive process.

Red algae are mostly aquatic, include such familiar organisms as sushi wrap, and are the sources of agar and carrageenan. Green algae are terrestrial, and are genetically related to all land plants.

“What we knew about red algae we learned from sequencing extemophiles—algae that live in extreme environments—because their genomes are relatively small,” says Debashish Bhattacharya, professor of ecology, evolution, and natural resources at Rutgers.

“But most red algae are mesophiles, which means they live in normal temperatures.

Using a new generation of gene sequencing machine, Bhattacharya was able to sequence the entire genome of Calliarthron tuberculosum and a comprehensive list of expressed genes—genes caught in the act of fulfilling their functions—for Porphyridium cruentum, two species of red algae, in just a couple of weeks.

His team was then able to compare the data to all the data available in protein banks, discovering that red and green algae shared half their genomes—and that red algae also shared a considerable part of its genome with other, non-algae organisms.

Details of the research are published in the journal Current Biology.

“The availability of next-generation sequencers has opened the window to generate sequences from all kinds of organisms,” Bhattacharya says.

“This has opened our eyes to how complicated the history of genes is in the tree of life. Here, we finally got genomic data for normal red algae, and that’s opened our eyes to, holy smoke, how complicated they are.”

The research has important practical implications, Bhattacharya says. “The ancestor gave rise to the algae that generated all the fuel we currently use in cars and planes, and the photosynthetic organelle they contain is the target for modern biofuel research using fast-growing algae.”

Knowing what they know about red and green algae will help scientists to figure out how they differ, and how those differences may be manipulated to create better algae for biofuel research, Bhattacharya says.

“These algae could be designed to incorporate desirable characteristics from both lineages.”

Researchers from the University of British Columbia; and the University of Buenos Aires contributed to the study.

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