Role ofDIVARICATAin the control of dorsoventral asymmetry inAntirrhinumflowers

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Abstract
Dorsoventral asymmetry of theAntirrhinumcorolla depends on expression of theCYCandDICHgenes in dorsal petals. One role of these genes is to inhibitDIVARICATA(DIV), a determinant of ventral identity. Therefore, incyc;dichdouble mutants ventral identity spreads all around the flower. We show thatDIVencodes a protein belonging to the MYB family of transcription factors. Early on in corolla development,DIVaffects specifically the growth of ventral and lateral petals but is transcribed in all petals. Analysis of a closely related gene suggests that the lack of effect on dorsal petals is not due to redundancy. More likely, therefore, DIV is regulated posttranscriptionally through a mechanism that depends onCYCandDICH. Later on,DIVaffects growth and cell types and is transcribed mostly in a single layer of cells of ventral and lateral petals. This late pattern may itself depend onDIVactivity because it fails to be established in a transcribed but inactivedivmutant and, conversely, spreads all around the flower incyc;dichdouble mutants.