Today, in simultaneous press conferences across the globe, an international consortium announced it had finished the first genome sequence of a higher plant. For plant biologists, the unraveling of the genetic code of this small mustardlike weed, Arabidopsis thaliana, offers a long-awaited window into the genetic makeup of all plants, including key crops. But more than that, this genome shows that plants may be much more sophisticated organisms than many biologists have imagined.

The consortium, which consists of labs in Europe, the United States, and Japan, determined the order of some 115 million bases along the five chromosomes make up the DNA of this weed. As part of that effort, they also ventured into the sequence and structure of the centromere, an important albeit rather inscrutable region of the chromosome that assists in chromosome pairing--a region most genome sequencers ignore. To date, chromosomes 1 and 5 have about three gaps each left to fill, far fewer, for instance, than the 1200 gaps in the Drosophila genome sequence. "It's by far the most high-fidelity multicellular eukaryotic genome to date," says Jeffrey Dangl, a molecular geneticist at the University of North Carolina, Chapel Hill.

Arabidopsis turns out to have a surprisingly high number of likely genes, some 25,500, as opposed to 13,600 in the fruit fly, consortium members report in the 14 December issue of Nature. That total comes impressively close to low-end estimates of the quota of human genes. "It says that you have to have more respect for plants," concedes Nobel laureate James Watson, co-discoverer of the double helical structure of DNA.

Moreover, comparisons between these genes and the genes in other organisms revealed several other surprises. Some 58% of the genome is duplicated. And about 100 Arabidopsis genes have counterparts in humans that cause disease, including genes involved in cystic fibrosis and breast cancer. Also, while many of the genes involved in basic cell functions are the same in this plant and animals, the set of genes for cell-to-cell communication vary dramatically between the two kingdoms. "[That] fits with the idea that multicellularity evolved separately [in plants and animals]," says plant geneticist Robert Martienssen of the Cold Spring Harbor Laboratory in New York.

These are the first of many insights expected to pour out of the genome, not just for learning about Arabidopsis but also about other plants. Daniel Cosgrove, president of the American Society of Plant Physiologists, expects that the sequence data will also speed the identification of genes to improve agriculture and the use of plants as energy sources or for cleaning up the environment. Thus, he adds, "This is a very special time in the whole history of plants."

--ELIZABETH PENNISI

Related site

The Arabidopsis Information Resource (TAIR)