APETALA2 is a gene involved in flower development, that has been characterized in Arabidopsis thaliana. Apetala2 is a transcription factor associated with meristem determination, flower identity and seed development. This factor contains a DNA binding motif of 68 amino acids; its function is well known in model plants but not in other plant species. The objective of this study is the molecular analysis of the APETALA2 ortholog in marigold during flower development. A cDNA was synthesized by RT-PCR from RNA of marigold flower primordia and the sequence was compared with the sequences already reported for other species. The mRNA expression was analyzed in buds, primordia and flowers, where a specific expression was observed at early stages. Two fragments of 242 bp and 1000 bp, were engineered with the gateway system to generate RNAi constructs (TeAP2RNAi-242 and TeAP2RNAi-100 respectively) that were introgressed into A. thaliana through Agrobacterium transformation. Transformed plants were selected and seeds were recovered to T1. RT-PCR assay showed a 50 and 90% suppression of mRNA in the TeAP2RNAi-242 and TeAP2RNAi-1000 respectively, indicating a silencing effect on the APETALA2 messenger from A. thaliana. The phenotypes showed a role for APETALA2 on the Tagetes erecta flower transition and floral organ identity.