Different outcomes for the MYB floral symmetry genesDIVARICATA and RADIALIS during the evolution of derivedactinomorphy in Plantago

摘要

The gene network that specifies flower shape in Antirrhinum majus (bilateral floral symmetryor zygomorphy) includes two MYB-class genes – RADIALIS (RAD) and DIVARICATA(DIV). RAD is involved in establishing the dorsal identity program and its role is to regulate thedomain of activity of DIV (the ventral identity program) by restricting it to ventral regions ofthe flower. Plantago is in the same family as Antirrhinum but has small, radially symmetrical(actinomorphic) flowers derived from a zygomorphic ancestral state. Here we investigate theMYB-class floral symmetry genes and the role they have played in the evolution of derivedactinomorphy in Plantago lanceolata. A DIV ortholog (PlDIV) but no RAD ortholog was identified in P. lanceolata. PlDIV isexpressed across all petals and stamens later in flower development, which is consistent withthe loss of RAD gene function. PlDIV expression in anther sporogenous tissue also suggeststhat PlDIV was co-opted to regulate cell proliferation during the early stages of pollen development. These results indicate that evolution of derived actinomorphy in Plantago involved completeloss of dorsal gene function, resulting in expansion of the domain of expression of theventral class of floral symmetry genes.