In 2010, the gene controlling pea flower colour – first studied by Gregor Mendel 150 years earlier ­­– was identified by researchers from New Zealand and overseas.

Mendel’s experiments on peas

Key principles of genetics were developed from Gregor Mendel’s ground-breaking experiments on inheritance in the 1860s. Mendel cross-bred pure lines of pea plants (Pisum sativum) and recorded the inheritance of visible traits, such as flower colour, stem length, pod shape and pod colour.

Read more about Mendel’s experiments and Mendel’s principles of inheritance

Mendel’s traits in the 21st century

In 2010, a team of researchers from Plant & Food Research in New Zealand, along with collaborators in the UK, France and the US, identified the gene that controls flower colour in peas, one of the 7 traits that Mendel followed.

Purple flowers accumulate anthocyanin pigment molecules, whereas white flowers do not. For this reason, the researchers speculated that the gene they were looking for was likely to regulate anthocyanin biosynthesis.

Finding the gene for pea flower colour

The researchers knew approximately where the gene was in the pea genome – its locus – because of genetic markers close by. Unfortunately, there wasn’t much information available about the pea genes in this region, and a full genome sequence wasn’t available. By comparing pea genes with genes in a similar region in plants with fully sequenced genomes, like barrel clover and petunia, they found a gene that was likely to affect anthocyanin pigment production.

A gene controlling pigment manufacture

The gene the researchers found encodes a transcription factor – a protein that switches the expression of genes on and off. This transcription factor switches on the expression of genes involved in making anthocyanin pigments in pea flowers, making them purple.

When the researchers looked at the DNA sequence of the same gene in white-flowering pea plants. they noticed a difference in just 1 base. This single base change, from G to A, stops the gene being made into protein, so it can’t switch on expression of genes. The pea plants with this version of the gene don’t make anthocyanin pigments and have white flowers.

Confirming the gene function

To test the gene’s function, the researchers expressed the gene transiently in pea petals. They did this using biolistics – firing copies of the gene construct into pea petals from a gene gun. In areas of the petal where the gene was expressed, the flowers accumulated anthocyanin pigment and were coloured purple.

Identifying Mendel’s other pea genes

This is the 4th of the Mendel’s pea trait genes to be identified. Researchers have already identified the genes behind plant size, pea seed colour and seed shape.

Anthocyanins: important pigment molecules

Anthocyanin is responsible for red, blue and purple colours seen in many plants. Anthocyanin pigments are antioxidants – they mop up DNA-damaging free radicals that are released during photosynthesis, particularly during high light. This minimises damage to the plant’s DNA.

If we eat plants containing anthocyanin, the pigment molecules seem to make our own antioxidant systems more effective. This is part of the reason why having a mixed diet of colourful fruits and vegetables is good for our health. This is also why plant breeders are interested in breeding fruits that contain more anthocyanin pigments. Find out more about this in resources on breeding red-fleshed apples.

Useful links

The full article on the Identification of Mendel’s white flower character is freely available at PLoS One

Video of Roger Hellens explaining the discovery of the gene controlling pea flower colour.

 

    Published 16 August 2011