Diversification and co‐option of RAD‐like genes in the evolution of floral asymmetry

Abstract

SummaryTo understand how changes in gene regulatory networks lead to novel morphologies, we have analysed the evolution of a key target gene, RAD, controlling floral asymmetry. In Antirrhinum, flower asymmetry depends on activation of RAD in dorsal regions of the floral meristem by the upstream regulators CYC and DICH. We show that Arabidopsis, a species with radially symmetric flowers, contains six RAD-like genes, reflecting at least three duplications since the divergence of Antirrhinum and Arabidopsis. Unlike the situation in Antirrhinum, none of the Arabidopsis RAD-like genes are activated in dorsal regions of the flower meristem. Rather, the RAD-like genes are expressed in distinctive domains along radial or ab-adaxial axes, consistent with a range of developmental roles. Introduction of a RAD genomic clone from Antirrhinum into Arabidopsis leads to a novel expression pattern that is distinct from the expression pattern of RAD in Antirrhinum and from the endogenous RAD-like genes of Arabidopsis. Nevertheless, RAD is able to influence developmental targets in Arabidopsis, as ectopic expression of RAD has developmental effects in this species. Taken together, our results suggest that duplication and divergence of RAD-like genes has involved a range of cis-and transregulatory changes. It is possible that such changes led to the coupling of RAD to CYC regulation in the Antirrhinum lineage and hence the co-option of RAD had a role in the generation of flower dorsoventral asymmetry.

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“…Boraginaceae, Solanales, Gentianales; figure 2a). In the distantly related model species Arabidopsis thaliana (rosid lineage), CYC-and RAD-like genes and gene products do not seem to be directly regulated by one another [57,65], but the phylogenetic distance makes it difficult to draw conclusions about when the CYC/RAD network interactions evolved. Elsewhere within asterids, the role of CYC-like genes in independent transitions to bilateral flower symmetry has been investigated in Dipsacales and Asterales (figures 2a and 4).…”

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