Tiny plant poised to yield big payoffs in environment and energy

With the genomes of humans and several insects, animals and crop plants mapped or sequenced, biologists are turning their attention to single-celled algae no thicker than a human hair. Among the possible payoffs: crops requiring less fertilizer, a source of renewable energy and a new source for novel proteins.

The algae, Chlamydomonas reinhardtii , already are an important biological model for genetics research. Now, the complete genome of the plant’s chloroplast has been sequenced by scientists at the Boyce Thompson Institute (BTI) for Plant Research located on the campus of Cornell University. The chloroplast is the area of the plant that harvests light energy. Details of the sequencing (that is, determining the base sequence of each of the ordered DNA fragments) appear in the latest issue of the journal The Plant Cell (November 2002).

The complete chloroplast genome sequence, says David Stern, a biologist and vice president for research at BTI, a not-for-profit research organization, has made it possible to test the response of Chlamydomonas (pronounced CLAMMY-doe-moan-us) to various environmental stresses, work that is reported in an accompanying article in The Plant Cell . In addition, the organism’s nuclear genome is being sequenced by the Joint Genome Institute, a unit of the Department of Energy.

One type of environmental stress being explored, says Stern (who also is an adjunct professor of plant biology at Cornell) is that of response to phosphates. The developed world, he says, puts too much phosphorous fertilizer on plants and crops. “It turns out that Chlamydomonas shares many of the responses to phosphate stress with crop plants. Working with Chlamydomonas, we can quickly test ways to improve tolerance or adaptation, perhaps leading to ways of engineering crop plants for the same purpose,” he says.

If fertilizer use were decreased, phosphorous runoff into creeks, streams and lakes might be diminished. Phosphate leaching is a prime cause of algae blooms in lakes and ponds around agricultural areas.

The algae might also one day be a source of hydrogen, a clean-burning fuel. At present, hydrogen used in a type of battery called a fuel cell (still in its infancy for powering cars and boats) is extracted from natural gas — a nonrenewable resource. A group led by Anastasios Melis, a professor at the University of California-Berkeley, is exploring the use of Chlamydomonas as a renewable hydrogen source.

Additional applications include using the Chlamydomonas chloroplast as a “bioreactor” to create, or “over-express,” a variety of novel proteins for agricultural, industrial and biomedical purposes, says Jason Lilly, a BTI postdoctoral researcher.

Chlamydomonas plants have been useful to science for a century in both agriculture and energy research. In nature, the organisms are widely present in fresh and brackish water, all kinds of soils, underwater thermal vents and even under the Antarctic ice shelf. One species of Chlamydomonas sports a red pigment — as protection from solar damage — and is found in alpine or arctic regions. These red algae create a phenomenon referred to as “red snow.” The organism’s global dispersion demonstrates the algae’s adaptive nature, says Stern.

“Chlamydomonas is a relatively simple organism and easy to work with,” says Stern. “One drawback, however, is that despite its long history as a laboratory organism, the scientific community has lacked so-called genomics resources. This long-awaited part of the genetic toolbox promises to be a boon for scientists.”

Completing the Chlamydomonas chloroplast genome sequence is part of a larger Chlamydomonas Genomic Initiative, spearheaded by Arthur Grossman of Stanford University, working at the Carnegie Institution of Washington. Stern’s chloroplast genome studies, a project that began three years ago, have been supported by grants from the National Science Foundation and the National Institutes of Health.

In addition to Stern and Lilly, the other authors and researchers are: Jude E. Maul, BTI laboratory researcher; Liying Cui, Claude W. dePamphilis and Webb Miller of Pennsylvania State University; and Elizabeth Harris of Duke University. The articles, “Chlamydomonas reinhardtii plastid chromosome: Islands of genes in a sea of repeats” and “The Chlamydomonas reinhardtii organellar genomes respond transcriptionally and post-transcriptionally to abiotic stimuli,” are scheduled to appear in the November printed issue and the online edition of The Plant Cell .