SummaryFlowering time in many plants is triggered by environmental factors that lead to uniform¯owering in plant populations, ensuring higher reproductive success. So far, several genes have been identi®ed that are involved in¯owering time control. AGL20 (AGAMOUS LIKE 20) is a MADS domain gene from Arabidopsis that is activated in shoot apical meristems during the transition to¯owering. By transposon tagging we have identi®ed late¯owering agl20 mutants, showing that AGL20 is involved in¯owering time control. In previously described late¯owering mutants of the long-day and constitutive pathways of¯oral induction the expression of AGL20 is down-regulated, demonstrating that AGL20 acts downstream to the mutated genes. Moreover, we can show that AGL20 is also regulated by the gibberellin (GA) pathway, indicating that AGL20 integrates signals of different pathways of¯oral induction and might be a central component for the induction of¯owering. In addition, the constitutive expression of AGL20 in Arabidopsis is suf®cient for photoperiod independent¯owering and the overexpression of the orthologous gene from mustard, MADSA, in the classical short-day tobacco Maryland Mammoth bypasses the strict photoperiodic control of¯owering.