Evolution of 2S albumin seed storage protein genes in the Brassicaceae

Abstract

Abstract The DNA and deduced amino acid sequences of the 2S albumin seed storage protein genes from some members of the Brassicaceae, including the genera Brassica , Raphanus , Sinapis (all tribe Brassiceae) and Arabidopsis (tribe Sysimbrieae), were analysed to infer their phylogenetic relationships. Analysis of the DNA sequence of the 5′ and 3′ untranslated flanking regions provided evidence that a number of the 2S albumin genes were duplicated prior to the Brassiceae-Sysimbrieae split. Analysis of the deduced amino acid sequence of the protein coding regions suggested that many of these sequences have undergone concerted evolution. Three distinct clusters of 2S albumin genes were identified within the Brassiceae; one cluster consisted entirely of Sinapis sequences, the second cluster consisted of sequences from B. oleracea , and B. juncea and some sequences from B. napus , and the third cluster consisted of sequences from B. rapa , B. nigra, R. sativus , and the remaining B. napus sequences. Comparison of the gene tree of the coding regions with a conventional species tree suggests that the protein coding sequences in the latter two clusters were created by duplication and subsequent divergence in the common ancestor of these species, and that sequences derived from one of the clusters have been eliminated from the genome of each species. These results suggest that both gene duplication and non-reciprocal DNA exchanges have played a role in the evolution of the 2S albumin genes of the Brassicaceae.