Genomic evolution and complexity of the Anaphase-promoting Complex (APC) in land plants

Here, we describe an in-depth search for APC subunits and activator genes in the Arabidopsis, rice and poplar genomes. Also, searches in other genomes that are not completely sequenced were performed. Phylogenetic analyses indicate that some APC subunits and activator genes have experienced gene duplication events in plants, in contrast to animals. Expression patterns of paralog subunits and activators in rice could indicate that this duplication, rather than complete redundancy, could reflect initial specialization steps. The absence of subunit APC7 from the genome of some green algae species and as well as from early metazoan lineages, could mean that APC7 is not required for APC function in unicellular organisms and it may be a result of duplication of another tetratricopeptide (TPR) subunit. Analyses of TPR evolution suggest that duplications of subunits started from the central domains.The increased complexity of the APC gene structure, tied to the diversification of expression paths, suggests that land plants developed sophisticated mechanisms of APC regulation to cope with the sedentary life style and its associated environmental exposures.Cell proliferation is controlled by an universally conserved molecular machinery in which the key players are cyclin-dependent kinases (CDK) and cyclins (reviewed in [1]). Eukaryotes have therefore evolved elaborate mechanisms for CDK regulation. An irreversible mechanism of CDK down-regulation is destruction of cyclin subunits [2,3]. At the G1- to S-phase and metaphase to anaphase transitions, CDKs are irreversibly inactivated by ubiquitin-mediated proteolysis of cognate cyclins [4]. Degradation of protein substrates through the ubiquitin-proteasome pathway involves the activity of different E3 ligases, among them the anaphase-promoting complex (APC). The APC was first identified based on its role in facilitating the multiubiquitination and targeting of A- and B-type cyclins for proteasome-mediated destruction during mitos