How the orchid came to her lip

Geneticists are explaining the mechanism for the development of biodiversity

Paphiopedilum godefroyae © Wolfgang Apel / GFDL
Read out

They are considered the divas among the flowering plants and fascinate by extravagant flower shapes and bright colors - the orchids. But how did you come to their mirror-symmetrical flowers with the characteristic lip? This was previously unknown. Now Jena scientists have taken a decisive step further in solving this problem.

In the current issue of the journal Trends in Plant Science, geneticists publish a hypothesis based on molecular genetic data on how the "orchid principle" could have evolved.

Although there are extremely diverse forms, all orchid types have one thing in common: "In contrast to the flowers of relatively close relatives such as lilies or tulips, orchid flowers have only one plane of symmetry, " explains Professor Günter Theissen from the University of Jena. "This mirror symmetry contributes significantly to the characteristic appearance of the orchid flower, " the geneticist points out.

Gene switch examined

Unlike tulips or lilies, which have six identical petals, orchids have different-looking petals. "In addition to three 'sepals', they have two 'petals' and a 'lip', " according to Theisse's colleague Mariana Mondragón-Palomino. The Mexican-born scientist has been researching the flower development of orchids on a molecular genetic level since 2006.

Mariana Mondragón-Palomino has been researching in Theißen's laboratory since 2006 as part of a project sponsored by the Volkswagen Foundation and is investigating the flower development of orchids molecularly genetically. © Peter Scheere / FSU

The morphological differences of the flower organs of the orchids have their origin on genetic level. While in close relatives of the orchids a gene that controls the development of all six petals is in a simple copy, the appearance of the orchid flower organs determines four different control genes of this type. Thus, two control genes are switched on to develop the sepals, three in the petals and all four Genschalter are active for the formation of the lip. display

This principle could be demonstrated in a number of very different types of orchids, so it is very likely to be a general principle, "said Thei en. Also, how the orchid-specific control genes have evolved in the course of evolution, have found out the geneticists of the Jena University. "These have doubled twice in orchids, " explains Thei en.

Gene doubling as a success principle of evolution

Subsequently, the formerly identical genes specialized and acquired new functions. However, this principle of gene duplication and subsequent specialization is not only found in orchids. "It is rather a widespread principle that evolutionary innovations - and, as a consequence - biodiversity and biodiversity can emerge, " Thei en points out. The orchids have made this strategy - with perhaps more than 30, 000 species - an extremely successful group of plants.

Next, the Jena geneticists want to see if their hypothesis is true even in the case of very primitive orchids that have not yet been studied, because they are very rare and difficult to obtain. So far, the hypothesis is based on gene expression studies. The researchers therefore also want to study the function of the duplicated genes as soon as possible using genetically modified phenotypes. Corresponding studies are quite tedious in orchids but for technical reasons. In addition, the researchers are interested in whether the principle can also be found in other plants. "We know that other flowering plants have formed lips, " said Thei en. "It will be interesting to see if these gene duplications have contributed to their formation."

(idw - University of Jena, 21.02.2008 - DLO)