Analysis of gymnosperm two-AP2-domain-containing genes

AINTEGUMENTA (ANT) and APETALA2 (AP2) are transcription factors that are involved in several developmental processes in Arabidopsis thaliana. They are similar in structure, containing two AP2 domains, and have partially redundant functions in reproductive organ development. Expression and functional analyses of ANT and AP2 homologs have been performed previously in almost all angiosperms. In this study, one ANT homolog and two AP2 homologs were isolated from the gymnosperm Pinus thunbergii and were named PtANTL1, PtAP2L1, and PtAP2L2. PtANTL1 is the first reported gymnosperm ANT homologous gene. Based on a gene tree constructed with sequences of all A. thaliana two-AP2-domain-containing genes, it is likely that PtANTL1 and ANT, and likewise PtAP2L1 and AP2, are orthologs. The expression patterns of PtANTL1/PtAP2L1/PtAP2L2 were examined with Southern hybridization of the quantitative RT-PCR products and in situ hybridization. PtANTL1 and PtAP2L1 had almost identical expression patterns in the analyzed organs, and PtANTL1/PtAP2L1/PtAP2L2 were continually expressed in the developing female cone. Our analysis suggests that gymnosperms have orthologs to both ANT and AP2, and that the most recent common ancestor of extant seed plants has two type AP2 subfamily genes, ANT-like and AP2-like, involved in the development of female reproductive organs.