The activity of plant meristems, which form new tissues and organs throughout a plant's life, determines the architecture of different plants. On , George Chuck and colleagues reveal how the APETALA2 (AP2)-like genes indeterminate spikelet1 (ids1) and sister of indeterminate spikelet1 (sid1) determine inflorescence (the structure that displays a plant's flowers) architecture in maize. Grass flowers are organised on small branches called spikelets. In maize, the spikelet meristem is determinate - it initiates the formation of one floral meristem and then converts into a second floral meristem. ids1controls the timing of this conversion. The authors show that ids1functions with sid1 to control inflorescence meristem branching,floral meristem initiation and spikelet meristem determinacy. ids1and sid1, they also report, are major targets of the tasselseed4 microRNA. Furthermore, ids1 and sid1,like Arabidopsis AP2, repress the expression of AGAMOUS-like transcription factors. However, AP2 mutants in Arabidopsisstill make flowers, whereas ids1/sid1 mutants do not,revealing that AP2 genes have probably adopted different meristem functions during plant evolution.
