Expression divergence of the AGL6 MADS domain transcription factor lineage after a core eudicot duplication suggests functional diversification

BACKGROUND: Because of their known role as transcriptional regulators of key plant developmental processes, the diversification of MADS-box gene function is thought to be a major driving force in the developmental evolution of plants. Yet the function of some MADS-box gene subfamilies has remained elusive thus far. One such lineage, AGL6, has now been functionally characterized in three angiosperm species, but a phylogenetic framework for comparison of AGL6 gene function is currently missing. RESULTS: Based on phylogenetic analyses of newly isolated and EST-based sequences, we describe the duplication history of the AGL6 subfamily in angiosperms. Our analyses provide support for four ancient duplications in the evolution of the AGL6 lineage: one at the base of core eudicots resulting in euAGL6 and AGL6-like gene clades, one during basal angiosperm diversification and two in monocot evolution. To investigate whether the spatial domains in which AGL6 genes function have diverged after duplication, we use quantitative Real Time PCR. We show that the core eudicot AGL6-like clade acquired expression in vegetative tissues, while its paralog euAGL6 remains predominantly confined to reproductive tissues. CONCLUSIONS: These and previous data lead us to propose that the AGL6 lineage in core eudicots, in addition to functions related to the expression in reproductive structures, may have acquired a function in developmental transitions of vegetative shoots.