Genetic Control of Plant Architecture in Foxtail Millet (Setaria italica)

The patterns of branching that characterize the vegetative architecture of a plant are built up over its lifetime.  Species differ in their branching patterns, yet different lengths of time to maturity make taking developmentally comparable measurements challenging.  However, one developmental stage that can be used to compare species developmentally is the onset of flowering, which signals a change from vegetative to reproductive growth for the plant. The transition of the vegetative apical meristem to an inflorescence meristem terminates the production of vegetative buds on a branch, and may also alter hormonal fluxes such that some buds are released from suppression and subsequently elongate.  We have been studying patterns of branching at flowering in domesticated foxtail millet (Setaria italica)and its wild progenitor green millet (S. viridis).  Green millet is a typical wild grass that shows great developmental plasticity in height and branching patterns, whereas foxtail millet has much reduced branching, greater height and comparatively delayed flowering.  Through analysis of branching architecture in an F7 RIL population derived from a cross between these two species we have detected two patterns of growth, one where delay of flowering leads to taller specimens with reduced branching and the second where a delay of flowering is accompanied by an increase in tiller production.  We are investigating these different branching patterns using quantitative and candidate gene approaches to establish the genetic and environmental factors causing differences in vegetative architecture.