Gymnosperm B-sister genes may be involved in ovule/seed development and, in some species, in the growth of fleshy fruit-like structures

† Background and Aims The evolution of seeds together with the mechanisms related to their dispersal into the environmentrepresented a turning point in the evolution of plants. Seeds are produced by gymnosperms and angiospermsbut only the latter have an ovary to be transformed into a fruit. Yet some gymnosperms produce fleshystructures attractive to animals, thus behaving like fruits from a functional point of view. The aim of this work isto increase our knowledge of possible mechanisms common to the development of both gymnosperm and angiospermfruits.† Methods B-sister genes from two gymnosperms (Ginkgo biloba and Taxus baccata) were isolated and studied.The Ginkgo gene was also functionally characterized by ectopically expressing it in tobacco.† Key Results In Ginkgo the fleshy structure derives from the outer seed integument and the B-sister gene is involvedin its growth. In Taxus the fleshy structure is formed de novo as an outgrowth of the ovule peduncle, and the B-sistergene is not involved in this growth. In transgenic tobacco the Ginkgo gene has a positive role in tissue growth andconfirms its importance in ovule/seed development.†Conclusions This study suggests that B-sister genes have a main function in ovule/seed development and a subsidiaryrole in the formation of fleshy fruit-like structureswhenthe latter have an ovular origin, as occurs in Ginkgo. Thus,the ‘fruit function’ of B-sister genes is quite old, already being present in Gymnosperms as ancient as Ginkgoales, andis also present in Angiosperms where a B-sister gene has been shown to be involved in the formation of theArabidopsis fruit.