Analysis of flower genes reveals the fate of an ancient gene duplication

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Analysis of flower genes reveals the fate of an ancient gene

duplication

http://www.medicalnewstoday.com/medicalnews.php?newsid=29523

23 Aug 2005

In a step that advances our ability to discern the ancient

evolutionary relationships between different genes and their

biological functions, researchers have provided insight into the

present-day outcome of a single gene duplication that occurred over a

hundred million years ago in an ancestor of modern plants. The work

is reported in Current Biology by a team led by n Davies of the

University of Leeds, England.

Gene duplication--a relatively uncommon event in which a single copy

of a gene is transformed into two separate copies--is thought to play

a key role in the evolution of new gene functions. Duplications are

important because they effectively allow at least one of the gene

copies to evolve while the (likely important) function of the

original gene can remain intact. In this way, the duplication of pre-

existing genetic information provides the raw material from which new

gene functions can evolve, thereby contributing to the evolution of

genetic complexity and the evolution of sophisticated life forms.

Very many such gene-duplication events have shaped the evolution of

today's living species, but tracing the evolution of a specific

single gene over millions of years of evolution--and over potentially

several gene-duplication events--can pose a significant challenge.

One way in which this can be overcome is for researchers studying a

particular modern-day gene to look at neighboring genes in different

related species. Genes derived from a common ancestral gene region

will still share similarities in neighboring gene sequences, both in

terms of gene identity and the order such sequences appear within the

chromosome. This kind of preserved gene order is known as genome

synteny.

In the new work, researchers have used synteny to clarify the

evolution of genes essential for the development of floral

reproductive organs, stamens and carpels. The subjects of their work

were two genes that appear to play identical functions in two

different plant species: the AGAMOUS (AG) gene of the mustard plant

Arabidopsis thaliana and the PLENA (PLE) gene of the snapdragon,

Antirrhinum majus. Both genes are required for the development of

flower reproductive structures, and when these genes are mutated, the

plants form so-called double flowers, in which petals and sepals

replace stamens and carpels. AG and PLE are very closely related

genes, and they clearly have nearly identical function, suggesting

that they are derived from the same single gene inherited from a

common ancestor. However, analysis of synteny in the AG and PLE

regions unambiguously showed that AG and PLE are not derived from the

same ancestral gene, but that they instead represent two different

products of a gene-duplication event that occurred around 125 million

years ago in a common ancestor of Arabidopsis and Antirrhinum. The

other genes created in that ancient gene-duplication event became

altered, in different ways, so that they now have new functions in

Arabidopsis and Antirrhinum.

These findings provide one of the first demonstrations of how an

essential developmental function can be randomly assigned to either

product of a gene-duplication event. The work defines a new standard

for the evidence required to establish the evolutionary relationships

of genes from different species.

The researchers include Barry Causier, Ingram and n

Davies of the University of Leeds in Leeds, UK; Castillo and

Zsuzsanna Schwarz-Sommer of the Max-Planck-Institut für

Züchtungsforschung in Köln, Germany; and Junli Zhou and Yongbiao Xue

of the Chinese Academy of Sciences in Beijing, China. This work was

funded by grants from the Biotechnology and Biological Sciences

Research Council to B.D. and B.C. and from the British Council to

B.D. and Z.S.-S.

Causier et al.: " Evolution in action: following function in

duplicated floral homeotic genes. " Publishing in Current Biology,

Vol. 15, 1508-1512, August 23, 2005. DOI 10.1016/j.cub.2005.07.063

http://www.current-biology.com

Cell Press

http://www.cellpress.com