EXTRAPETALS allows cymose branching in petunia by transiently repressing floral identity in sympodial meristems

Cymes and racemes form two broad types of inflorescence architecture. Racemes are monopodial and bear axillary flowers, but in cymes the main stem ends in an apical flower and is continued sympodially by a series of lateral shoots. In these shoots floral identity is delayed by a previously unknown mechanism. We show that the MADS-box transcription factor EXTRAPETALS (EXP) transiently represses floral identity in the sympodial meristems of petunia. While cymose branching is inhibited in exp, loss-of-function of the EXP homologs SVP and AGL24 from Arabidopsis causes the premature activation of floral organ identity genes in floral meristems, but this does not affect racemose branching. Our data indicate that the repression of floral identity that determines cymose and racemose body plans relies on distinct pathways that have no obvious mechanistic or evolutionary link, and suggest an evolutionary scenario in which cymes and racemes adopted similar means to different ends. !"#$%&'()&#*+,,---62 "012.1""---"34$5