The petunia floral pathway: target genes of ALF, DOT and EVG

The specification of floral identity of meristems in petunia requires floral meristem identity genes, ABERRANT LEAF AND FLOWER (ALF), DOUBLE TOP (DOT) and EVERGREEN (EVG). In order to further characterize the role of these genes in inflorescence and flower development, we employed two complementary approaches to find their early target genes. We compared the gene expression profiles of single, double and triple mutants, and we constructed post-translationally inducible forms of the three corresponding proteins. As ALF, DOT and EVG encode very different types of proteins that are expressed in distinct patterns, we expected to find three different sets of target genes. Here we show that the ALF, DOT and EVG pathways converge earlier than expected: at the control of ALF activity. We found that the transcriptomes of alf and dot mutants are very similar and that DOT is a direct activator of ALF target genes, supporting the idea that DOT is involved in the post-translational activation of ALF. DOT is strongly down regulated in evg mutants and the flowers reappear when DOT is constitutively expressed in an evg mutant background. This led to the idea that EVG indirectly promotes floral identity in petunia by relieving the repression of DOT. We conclude that alf, dot and evg mutants lack flowers for one common reason, namely the failure to generate an activated ALF protein that can trigger the transcription of downstream genes. Altogether, these data point towards a mechanism of floral meristem and floral organ identity specification with only a limited number of steps and involved genes. !"#$%&'()&#*+,,---.5 "/01$0""---"2345