Wetenschap - 15 oktober 2011

A step closer to explaining diversity of cabbage

Cabbage comes in many shapes and sizes, thanks to its wide genetic variation, researchers have concluded after sequencing the genome of Brassica rapa.

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The brassica family is well-represented in the vegetable section of the supermarket. Cauliflower, red cabbage and broccoli were all bred from the cabbage species Brassica oleraciea. Its sister species Brassica rapa was the source of vegetables such as the Chinese cabbage and the turnip. But it is not clear quite where this large variety in nature came from. Plant scientists guess that there is a very large genetic variation in cabbage plants.

Flowering time
‘The genome of the Chinese cabbage, a B. rapa crop, does indeed provide evidence of this’, explains Guusje Bonnema, assistant professor of Plant Breeding and member of the research team that reported its findings in this month´s Nature genetics. ´We see a strikingly large number of genes involved in regulating flowering time. This varies according to crop type from twenty days to as much as two years.´ A clear link, then, between gene abundance and diversity. The large number of genes involved in the hormonal system, which governs the formation of the plant, also supports the hypothesis.

Tripled
The researchers have an explanation for the source of these extra genes. It has been known for a while that the brassicas tripled their genetic material between five and nine million years ago. This is quite a common occurrence in plants, and afterwards, ‘superfluous’ genes mutate and disappear en masse. But a few groups of genes do seem to be kept and to make the eventual diversity of cabbage possible.
A fuller picture
Bonnema warns that this is still not a definitive answer to the puzzle. Future research is needed, especially on other crops such as turnips and Chinese cabbage, in order to get a fuller picture. ‘The first genome sequence of B. oleracea will be published soon’, says Bonnema. ‘After that we would really like to map another hundred genomes, including those of kohlrabi, cauliflower and broccoli.’ These data are expected to clarify whether there is such a large genetic variation in these plants too. Bonnema is also curious as to which genes are responsible for specific characteristics, such as the large leaves of red and white cabbage plants.
The brassica family is well-represented in the vegetable section of the supermarket. Cauliflower, red cabbage and broccoli were all bred from the cabbage species Brassica oleraciea. Its sister species Brassica rapa was the source of vegetables such as the Chinese cabbage and the turnip. But it is not clear quite where this large variety in nature came from. Plant scientists guess that there is a very large genetic variation in cabbage plants.

Flowering time
'The genome of the Chinese cabbage, a B. rapa crop, does indeed provide evidence of this', explains Guusje Bonnema, assistant professor of Plant Breeding and member of the research team that reported its findings in this month´s Nature genetics. ´We see a strikingly large number of genes involved in regulating flowering time. This varies according to crop type from twenty days to as much as two years.´ A clear link, then, between gene abundance and diversity. The large number of genes involved in the hormonal system, which governs the formation of the plant, also supports the hypothesis.

Tripled
The researchers have an explanation for the source of these extra genes. It has been known for a while that the brassicas tripled their genetic material between five and nine million years ago. This is quite a common occurrence in plants, and afterwards, 'superfluous' genes mutate and disappear en masse. But a few groups of genes do seem to be kept and to make the eventual diversity of cabbage possible.
A fuller picture
Bonnema warns that this is still not a definitive answer to the puzzle. Future research is needed, especially on other crops such as turnips and Chinese cabbage, in order to get a fuller picture. 'The first genome sequence of B. oleracea will be published soon', says Bonnema. 'After that we would really like to map another hundred genomes, including those of kohlrabi, cauliflower and broccoli.' These data are expected to clarify whether there is such a large genetic variation in these plants too. Bonnema is also curious as to which genes are responsible for specific characteristics, such as the large leaves of red and white cabbage plants. 
 

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