Evolution of the APETALA2 Gene Lineage in Seed Plants

Gene duplication is a fundamental source of functional evolutionary change and has been associated with organismal diversification and the acquisition of novel features. The APETALA2/ETHYLENE RESPONSIVE ELEMENTBINDING FACTOR (AP2/ERF) genes are exclusive to vascular plants and have been classified into the AP2-like and ERF-like clades. The AP2-like clade includes the AINTEGUMENTA (ANT) and the euAPETALA2 (euAP2) genes, both regulated by miR172. Arabidopsis has two paralogs in the euAP2 clade, namely APETALA2 (AP2) and TARGET OF EAT3 (TOE3) that control flowering time, meristem determinacy, sepal and petal identity and fruit development. euAP2 genes are likely functionally divergent outside Brassicaceae, as they control fruit development in tomato, and regulate inflorescence meristematic activity in maize. We studied the evolution and expression patterns of euAP2/TOE3 genes to assess large scale and local duplications and evaluate protein motifs likely related with functional changes across seed plants. We sampled euAP2/TOE3 genes from vascular plants and have found three major duplications and a few taxon-specific duplications. Here, we report conserved and new motifs across euAP2/ TOE3 proteins and conclude that proteins predating the Brassicaceae duplication are more similar to AP2 than TOE3. Expression data show a shift from restricted expression in leaves, carpels, and fruits in non-core eudicots and asterids to a broader expression of euAP2 genes in leaves, all floral organs and fruits in rosids. Altogether, our data show a functional trend where the canonical A-function (sepal and petal identity) is exclusive to Brassicaceae and it is likely not maintained outside of rosids.