The role of the APETALA1-like gene PIE07 in petunia

In Arabidopsis the floral identity of meristems is specified by the expression of a handful of genes that are activated upon the cues from several pathways leading to flowering. One of these genes is LEAFY (LFY) from Arabidopsis, which encodes a transcription factor that directly activates the expression of the floral identity MADS-box gene APETALA1 (AP1). In petunia, LFY ortholog ABERRANT LEAF AND FLOWER (ALF) is also required for floral meristem identity, although its expression pattern and genetic regulation has diverged substantially from LFY. We here show that PROTEIN INTERACTING WITH EXP #07 (PIE07) is the closest petunia AP1 homolog described to date and that PIE07 and AP1 are functionally exchangeable proteins. Surprisingly, neither ectopic expression of AP1 of PIE07, nor mutation of PIE07 has any effect on the specification of floral meristem identity in petunia, whereas ectopic expression promptly induces flowering in Arabidopsis. Moreover, the role of AP1 in the specification of the identity of the organs in the outer whorls of the flower is not conserved in petunia. These data indicates that also the networks downstream of LFY and ALF have drastically changed during evolution, and shows that the genetic specification of floral meristem identity in Arabidopsis and petunia has diverged further than ever anticipated. H1.6_ELSKE.indd 132 17-05-11 13:18