Connecting gene expression and cytokinin signaling during meristem determinacy transition in the rice panicle

Structural complexity in the rice inflorescence (panicle) is determined by the activity of indeterminate meristems, which allow sequential branching events to occur but later acquire a determinate character that precludes the initiation of new growth axes. To better understand the underlying regulatory processes, we combined a detailed time-course of panicle development with tissue-specific sampling of meristems before and after the determinacy switch, monitoring global gene expression programs and hormone accumulation. This allowed the delineation of three dynamic transcriptional modules and the inference of gene regulatory networks highlighting hormone regulatory hubs associated with the indeterminate-to-determinate meristem transition. Our data confirm the importance of known regulators of inflorescence development and identify novel actors, notably genes encoding transcription factors, that were not previously described in the regulation of flowering. The combined biochemical and transcriptomic data support a model in which cytokinin signalling is particularly active during the proliferative branching phase, during which meristem maintenance is promoted while a feedback mechanism is also triggered, ultimately leading to the acquisition of determinate meristem fate later in development. HighlightInvestigating the molecular nature of rice inflorescence meristem determinacy, we studied temporal and spatial gene expression alongside hormone accumulation, identifying novel regulatory interactions and a key role for cytokinins.