Fig. 1. A model of inflorescence development. (A) The inflorescence meristem (IM, 1°) initiates (black arrows) spikelet pair meristems (SPM, 2°). The SPM then initiates a spikelet meristem (SM, 3°) on its flank, and then converts (blue arrows) into a SM. In a reiterative manner, each SM initiates one floret meristem (FM, 4°) and converts into a FM. Adapted from Irish (Irish, 1997b). (B) In the ear, wild-type spikelets (top) initiate the lower floret (1) which aborts (red) and then the spikelet converts into the upper floret (2) which develops into a functional flower (green). In rgo1 plants (bottom), the spikelet produces a third flower (3). In many cases the second flower also develops (green/red gradient). Owing to the distichous pattern of floret initiation by the spikelet, any odd numbered flower (1, 3, 5,...) will face the base of the ear, while even numbered flowers (2, 4, 6,...) face the tip of the ear. Any mutation that either increases or decreases floret number may result in a rgo phenotype.

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