Sequencing Output at Work - Resolving Carpel Gene Origins

Carpels are the female reproductive organs of flowering plants (angiosperms), enclose the ovules, and develop into fruits. The presence of carpels unites angiosperms and distinguishes them from all other plant groups suggesting that carpels are the most important autapomorphy of the angiosperms. Many transcriptional regulators and co-regulators essential for carpel development are encoded by diverse gene families and well characterized in Arabidopsis thaliana. Among these regulators are AGAMOUS (AG), CRABS CLAW (CRC), ETTIN (ETT), HECATE (HEC), LEUNIG (LUG), NGATHA (NGA), SEUSS (SEU), SHORT INTERNODE/STYLISH (SHI/STY), and SPATULA (SPT). Homologs of these carpel developmental regulators were sampled from the sequenced genomes of phylogenetically informative species, such as Physcomitrella patens, Selaginella moellendorfii, Picea glauca, Amborella trichopoda, and several other angiosperms. We review current knowledge on the gene family and function in carpel development of the selected genes. Careful phylogenetic analyses utilizing recently sequenced genomeswere carried out that provide a phylogenetic background for the different gene families and provide minimal estimates for the ages of these families. Our analyses show that LUG-, SEU-, and SHI/STY-like genes were already present in the Most Recent Common Ancestor (MRCA) of all land plants, AG- and SPT-like genes were present in the MRCA of seed plants and their origin coincides with the ξ Whole Genome Duplication (WGD) and CRC-, HEC, ETT-, and NGA-like genes are angiosperm specific, most likely resulting from the ε WGD. Our work shows that the carpel development regulatory network was not recruited from a preexisting network that has been modified to serve in carpel development. Rather, the network directing carpel development was patched together by recruiting very old modules and combining them with comparatively novel, angiosperm-specific genes.