Plants show greater complexity in gene arrangement

John H.Frenster frensasc at
Tue Feb 22 20:20:24 EST 2000

Wonderful review of an intriguing topic.
Concerning DNA, are regulatory genes found in plants ?
John Frenster <frenster at>

Rcjohnsen wrote:

> Chromosomes show plants' secret complexity
> O. Baker
> Sci News 156:389  Dec 18 & 25 99
>    They make life look so simple, but they do it with an enormous number of
> genes.  One and a half billion years after plants' lineage diverged from ours,
> our green cousins are finally receiving the credit they deserve.
>    In a major milestone, nearly 300 researchers working in the United States
> and Europe have detailed the exact DNA sequence of two chromosomes from a
> plant. In doing so, they've uncovered a surprisingly dense crowd of genes.
>    "Plants are a lot more complicated than we give them credit for," comments
> Elliot M. Meyerowitz, a molecular geneticist at the California Institute of
> Technology in Pasadena.
> Nearly 8,000 genes populate chromosomes 2 and 4 of the wild mustard plant
> Arabidopsis thaliana, the scientists report. The count dwarfs the recent gene
> estimate of about 550 for human chromosome 22 (SN: 12/4/99, p. 356).
> Because Arabidopsis has only five chromosomes, it probably doesn't exceed a
> person in overall genetic complexity.  However, worms and flies fall short of
> matching mustard gene-for-gene, says Meyerowitz.
>    "Plants do a lot of things that animals  don't," he adds. For example,
> plants tune their development to the circumstances into which they are born.
> "You get a very different plant in cold or warm, light or shade—but a fly is a
> fly every time," he says.
>    Separate teams of scientists tackled chromosomes 2 and 4 of Arabidopsis.
> Both groups report the sequences they elucidated in the Dec. 16 NATURE.
> Additional scientific teams scrutinizing the mustard plant's three remaining
> chromosomes expect to complete the task within a year.
>    The scientists made mustard their target because of the small size of its
> chromosomes—implying that they contain relatively little junk DNA interspersed
> with the genes. Arabidopsis is also a favorite laboratory organism of
> geneticists. The existing base of knowledge will enable scientists to
> capitalize quickly on revelations about the Arabidopsis genome.
>    Piecing together the interlacing roles of the myriad new genes presents a
> massive puzzle, yet many of the pieces are familiar. By comparing the sequences
> with those already reported for the mustard and other organisms, the
> researchers say that they can guess, at least roughly, the biochemical task
> performed by about 60 percent of the Arabidopsis genes.
> Even with the detailed role of their genes uncertain, the chromosomes provide
> biologists with a snapshot of plant evolution. Many genes have similar
> counterparts on the same chromosome, suggesting that Arabidopsis progenitors
> duplicated them in recent history. An entire quarter of chromosome 2 shows up a
> big chunk of chromosome 4. Biologists suspect that gene duplication has been a
> common route to new traits.
>    Gaps exist in both chromosome sequences around the knoblike centromeres.
> These regions contain repetitious sequences that stymie the technique that
> scientists use to break down genome and then assemble its sequence from small
> pieces.
> The 16 million bases of the long arm of chromosome 2, however, make up one of
> the longest continuous segments of DNA ever sequenced—second only to a piece of
> human chromosome 22 unveiled earlier this month.

John H. Frenster, M.D.                      Voice: 650/367-6483
Physicians' Educational Series             FAX:   650/364-1773
247 Stockbridge Avenue                    frenster at
Atherton, CA 94027-5446                 frensasc at
euchromatin: "the most active portion of the genome within the cell nucleus".

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