There has been a constant evolution in the domesticated plants because of the added " human selection factor". e.g. plants with bigger grain size or sweeter fruits etc were preferred by the farmers. They harvested crops with such added characters. This artificial selection gave an advantage to the newer varieties. Over time the original wild type varieties were dominated by the "selected ones" and the added characters became a general feature of the population. This led to the birth of new subspecies and species.
Studies in Arabidopsis thaliana (Cousin of Cabbage) have shown that floral homeotic genes are important for early identification of inflorescence meristem (developing reproductive primordia) as a floral meristem. Leafy, Apetala1 (AP1) and cauliflower (cal) are such genes. cal gene codes for a protein : a MADS-box transcription activator. The K domain of the protein is responsible for its dimerisation. Upon dimerisation Cal protein binds to DNA and assists transcription of genes involved in identification of floral meristem.
It was found out that in cauliflower plants the cauliflower gene indeed has a premature stop codon . This results in a truncated protein. This protein cannot dimerize and fails to function as a transcription activator. Hence floral meristem is not formed. Instead the inflorescence meristem branches again and again to form the curd like structure typical to cauliflower. Further studies in Arabidopsis have shown that mutation in both CAL and AP1 gene together cause formation of cauliflower curd like structure instead of flowers. in Arabidopsis plant. Thus it is these mutations that have turned the cabbage into a cauliflower or a broccoli or a kale! It is these simple changes that have led to the evolution of the Cole family of vegetables.
|Current Biology 1995, Vol 5 No 4: Arabidopsis flowers fail to develop and a cauliflower curd like structure is form in ap1 and cal mutant|
This is the magic of Biology, it can turn a cabbage into a cauliflower by tweaking a few molecules!
1. Origin of the cauliflower, Current Biology 1995, Vol 5 No 4
2. Lowman and Purugannan, Duplication of APETALA1 floral homeotic gene, Journal of Heredity 1999
3. Variation and Selection at the CAULIFLOWER Floral Homeotic Gene Accompanying the Evolution of Domesticated Brassica oleracea ,Michael D. Purugganan, Abee L. Boyles and Jane I. Suddith, Genetics 155: 855–862 ( June 2000)