Fig. 3
From: Origination and selection of ABCDE and AGL6 subfamily MADS-box genes in gymnosperms and angiosperms
Evolution of B-class genes (AP3/PI) and their roles in Arabidopsis thaliana, Oryza sativa, and Ginkgo biloba. Model 1: The progenitor of the B-class gene (Ba) primarily evolved from a PI lineage and generated the AP3 and PI lineages through duplication. However, it evolved the PI in gymnosperm before duplication of the B-class gene generated the AP3 lineage in the angiosperm. Arabidopsis represents Arabidopsis thaliana. Arabidopsis thaliana and Oryza sativa have AP3 and PI. Other angiosperms with the B-class gene also possess AP3 and PI. Model 2: A duplication generated the ancestral (Ba) AP3 and PI lineages and a subsequent duplication; however, the AP3 lineage was subsequently lost in gymnosperms. Arabidopsis represents Arabidopsis thaliana. Arabidopsis thaliana, Oryza sativa and other angiosperms with B-class genes have AP3 and PI