Reporter 451, 8 May 2000


Mutant snapdragons revealing the secret life of plants

Research at Leeds into the genetics of a commonly cultivated garden flower - the snapdragon, or Antirrhinum majus - has brought scientists much closer to an understanding of just how plants grow and develop.


Not a triffid - but the apical meristem of a normal Antirrhinum plant, showing the few cells that actually decide all aspects of plant growth above the ground. The scanning electron micrograph is by Dr Martin Kieffer.

The Centre for Plant Sciences (CPS) is at the forefront of international studies into the genetic makeup of the perennial plant. Of Mediterranean origin, the snapdragon spread throughout the Roman Empire, was first botanically described by Linnaeus nearly three centuries ago and has been intensively studied since the 1920s in Germany and the UK.


The mutant flower named by its Leeds discoverers after the Italian singer Farinelli

Advances in genetics and molecular biology are now making it possible to look at the plantís working in unprecedented detail, revealing more about how cells divide and differentiate to form distinct organs like leaves, sepals, petals and reproductive organs.

Dr Brendan Davies, leading work at the Leeds centre which has attracted about £1m in current funding, explained why Antirrhinum has become such an important model for research in genes and developmental biology, alongside the tiny weed Arabidopsis.


How the garden grows: in the grounds of Devonshire Hall, Leeds plant scientists Dr Hanma Zhang (left) and Dr Brendan Davies (second right) confer with Dr Cathie Martin of the John Innes Institute and Dr Justin Goodrich of Edinburgh University. Leeds hosted this year's international conference on the Antirrhinum

"Most laboratory work has been done on Arabidopsis, but Antirrhinum has a different growth pattern. The use of two very different model species allows us to see the processes of development more clearly. We can home in on core genes that regulate developmental patterns in plants and see what is species-specific," he said.

The Leeds work has looked at mutant snapdragons to identify which particular genes have been affected in the mutants. Such mutations occur commonly in nature: for instance, plants may produce double flowers or develop leaves in an odd pattern. One example studied here had a flower which appeared to be perfectly normal, but was reproductively male-sterile - the result of the loss of a single gene - which its Leeds discoverers named Farinelli, after the famous 18th-century Italian castrato singer.


Claim to fame: Farinelli, the 18th-century castrato singer, is commemorated in a mutant flower

Dr Davies and colleagues have concentrated on genes in the meristem, the growth region at the end of the shoot where cells are divided and assigned to the plantís various lateral organs.

They have found it possible, for example, to extract from the meristem of a snapdragon a gene known to specify snapdragon production in that species, and put it into another species where it will have the effect of turning sepals into petals.

"We can tell which gene specifies that a plant must produce petals, but not yet explain how it works," said Dr Davies. "For centuries, people have been breeding horticultural mutants, and molecular biology is beginning to establish how the regulator genes achieve their effects."

In another project, he is working with Professor Philip Gilmartin, also of the CPS, to apply todayís molecular technology to some very old mutations of primulas, like double-flowered varieties known since Elizabethan times. Fieldwork on this project involves frequent visits to garden centres, and occasionally dealing with major wholesale growers of primulas in Italy.

"For the producers, mutants can be a nuisance cluttering up their greenhouses - but for us they are a valuable resource," said Professor Gilmartin. One of his part-time doctoral students, Margaret Webster, happens to be the custodian of the UKís national collection of anomalous primulas.

The CPS also benefits from long-standing links with two research centres in Germany, the Max-Planck Institute in Cologne and IPK-Gatersleben in the former German Democratic Republic, where mutants of Antirrhinum were cultivated and catalogued over many years. German reunification made this extraordinary research resource available to scientists in western Europe, where powerful modern techniques of molecular biology could be applied.

The Leeds group has also been studying a snapdragon mutant, cupuliformis, which is unable to form normal leaves and flowers: instead, all its organs are stuck together, producing a very peculiar-looking plant. By studying this mutantís DNA, PhD student Irene Weir was able to identify the gene that plants use to define the boundaries of all their organs, opening up the possibility of understanding how and why different plants produce organs in different positions.

Last month, Leeds hosted the 10th international Antirrhinum conference, which attracted 100 experts from the USA, France, Germany, Spain, Italy and elsewhere.

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