Mapping origins of canola means increased crop yields, less fertiliser use

The study has shown new ‘polyploid’ species Brassica napus emerged much earlier than previously thought from two related vegetables species - cabbages, cauliflower and broccoli on one side and turnips and Chinese cabbage on the other.

The paper, ‘Early allopolyploid evolution in the post-neolithic Brassica napus oilseed genome’, published today in the journal Science presents evidence that this crop species most likely arose in the post-neolithic era, around 7,500 years ago, from the ancestor genomes of B. oleracea (cabbages, cauliflower, broccoli) and B. rapa (turnips, Chinese cabbage).

“This is a blink of an eye on an evolutionary timescale, and provides us with a unique opportunity to study the consequences of such an event, especially for a crop species,” said Professor Graham King, director of Southern Cross Plant Science.

Professor King has been involved in this endeavour from its outset more than a decade ago as one of a large team of international crop scientists who had the vision of piecing together the sequence of one of the most complex genomes studied to date.

“Human cultivation and breeding of B. napus morphotypes may have affected chromosome behaviour and organisation within this timespan, with subtle (epigenetic) changes superimposed on the DNA sequence where genes controlling valuable agronomic traits are located,” Professor King said.

“The research team successfully deciphered what appears to be one of the most duplicated and complex crop genomes. It appears that human cultivation and breeding of this relatively new species may have resulted in selection of ‘cut and paste’ exchanges between the original chromosomes, and that this has affected the interaction between genes controlling valuable agronomic traits.”

The family tree for rapeseed was first established nearly 80 years ago.

Over the past 60 years, the oilseed canola crop has undergone intensive breeding to optimise flowering behaviour, seed oil content and fatty acid composition, decrease nutritionally undesirable erucic acid and glucosinolates, and improve disease resistance.

“Having the complete reference genome sequence for canola provides us with an excellent tool to understand the available genetic diversity, to increase yields and reduce use of fertiliser inputs,” said Professor King.

“In particular, this new information provides unique insights into the early evolution of a domesticated polyploid and will facilitate the manipulation of useful variation, contributing to sustainable increases in oilseed crop production to meet growing demands for edible oils, biolubricants, and other natural products.

“Over the years, the international team has progressively solved this vast jigsaw at increasing resolution, and is now able to understand the evolutionary history of different variants of individual genes on each of the 19 chromosomes.”

Southern Cross University has an active research program focused on Brassica crops, with Professor King and colleagues now focused on understanding the subtle changes to DNA that affect how crops respond to different growing environments. In particular, they are looking at how crop plants can optimise the use of minerals and fertiliser from the soil.

With the canola genome comprising over a billion ‘letters’ of DNA, the computational science of bioinformatics is now an integral part of the research toolbox in Southern Cross Plant Science. As part of SCU’s contribution to the international research community, it now hosts the long-established website www.brassica.info, which compiles information on many aspects of Brassica genetics, genomics and traits of agronomic interest.

The University has also developed strong links with researchers in China, which produces the second largest harvest of canola in the world, more than four times that in Australia.

Southern Cross University scientists recently participated in a Group Mission to China, funded by the federal Department of Industry. The trip focused on developing research collaborations to improve grain and oilseed quality and included a visit to Huazhong Agricultural University in Wuhan, where Professor King holds a visiting position as Chutian Professor Chair, funded by Hubei province.
Photo: Deciphering the highly-duplicated genome of the post-neolithic recent allopolyploid Brassica napus. The triangle of relationships between Brassica crop species and their associated genomes, as originally outlined by U (1935). The genomes of the three diploid species A, B and C have combined in pairs to form three distinct allopolyploid species, each of which have also been domesticated. In this issue Chalhoub et al. deciphered the genome of the most highly duplicated eudicot, B. napus. They present evidence that B. napus (AC) most likely arose in the post-neolithic era, around 7,500 years ago. Human cultivation and breeding of B. napus morphotypes may have selected favourable homeologous exchanges, causing sub-genome restructuring and epigenetic crosstalk of regions containing genes controlling valuable agronomic traits. Artwork copyright © Graham King.