The genetic basis for inflorescence variation between foxtail and green millet (Poaceae)

Grass species differ in many aspects of inflorescence architecture, but in most cases the genetic basis of the morphological difference is unknown. To investigate the genes underlying the morphology in one such instance, we undertook a developmental and QTL analysis of inflorescence differences between the cereal grain foxtail millet and its presumed progenitor green millet. Inflorescence differences between these two species are the result of changes in primary branch number and density, spikelet number, and bristle (sterile branchlet) number; these differences also account for inflorescence variation within the clade of 300+ species that share the presence of bristles in the inflorescence. Fourteen replicated QTL were detected for the four inflorescence traits, and these are suggested to represent genes that control differences between the species. Comparative mapping using common markers from rice and maize allowed a number of candidate genes from maize to be localized to QTL regions in the millet genome. Searches of regions of the sequenced rice genome orthologous to QTL regions on foxtail millet identified a number of transcription factors and hormone pathway genes that may be involved in control of inflorescence branching.