title: Conservation of B class gene expression in the second whorl of a basal grass and outgroups links the origin of lodicules and petals.
abstract: Studies of flower development in core eudicot species have established a central role for B class MADS-box genes in specifying petal and stamen identities. Similarly in maize and rice, B class genes are essential for lodicule and stamen specification, suggesting homology of petals and lodicules and conservation of B class gene activity across angiosperms. However, lodicules are grass-specific organs with a morphology distinct from petals, thus their true homology to eudicot and nongrass monocot floral organs has been a topic of debate. To understand the relationship of lodicules to the sterile floral organs of nongrass monocots we have isolated and observed the expression of B class genes from a basal grass Streptochaeta that diverged before the evolution of lodicules, as well as the outgroups Joinvillea and Elegia, which have a typical monocot floral plan. Our results support a conserved role for B function genes across the angiosperms and provide additional evidence linking the evolution of lodicules and second whorl tepal/petals of monocots. The expression data and morphological analysis suggest that the function of B class genes should be broadly interpreted as required for differentiation of a distinct second floral whorl as opposed to specifying petal identity per se.
authors.affiliation: Division of Biological Sciences, Section of Cell and Developmental Biology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA.
authors.forename: Clinton J
authors.initials: CJ
authors.lastname: Whipple
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Zanis
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Kellogg
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Schmidt
mesh_terms: D035264:Flowers / Q000033:anatomy & histology / Q000235:genetics* / Q000254:growth & development* / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant; D026161:MADS Domain Proteins / Q000235:genetics; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D010802:Phylogeny; D006109:Poaceae / Q000145:classification / Q000235:genetics* / Q000254:growth & development* / Q000648:ultrastructure
chemical_list: D026161:MADS Domain Proteins