Frequent Parallel Loss of Bsister MADS-Box Genes in Brassicaceae Genomes

Gene death is a frequent and potentially important event during genome evolution. What exactly determines the probability of a gene to get lost is only poorly understood, however. We use the B_sister genes of Brassicaceae as a model system to better understand the gene and genome features that determine gene retention and loss. Duplication of an ancestral B_sister gene, probably during the γ-genome triplication event of core eudicots around 120 million years ago, gave rise to the clades of ARABIDOPSIS BSISTER (ABS)-like and GORDITA (GOA)-like genes. Even though ABS-like and GOA-like genes are closely related paralogs, their fates in the genomes of Brassicaceae are remarkably different. While ABS-like genes have been highly conserved and are involved in important developmental processes such as ovule and seed development, GOA-like genes frequently got lost, and their functional importance remains unclear. We have compared the structure, promoter activity and mRNA expression, and protein-protein interactions of ABS- and GOA-like genes and proteins from diverse Brassicaceae genomes. Our results corroborate the view that the probability of a gene to get lost is inverse proportional to the strength of gene expression, the number of protein interaction partners, and the strength of purifying selection. Our data help to recognize genes with a high chance to get lost in the future.