(A) WT maize with no tillers. (B) gt1 mutant with increased tiller growth (arrows). (C) In situ RNA hybridization of gt1 on a section through the maize shoot apex. Strong expression is observed in the leaves and provasculature of lateral buds (arrows and Inset) but not in the shoot apical meristem (*) or surrounding leaves. (D) Higher magnification of the lateral bud (Inset in C) shows Gt1 expression in the adaxial domain of surrounding leaf primordia but absent from the meristem (*). (E) GT1-YFP expression in both the leaf primordia and the axillary meristem of a lateral tiller bud. AxM, axillary meristem; LP, leaf primordia. (F) Model for light regulation of axillary bud growth in maize. Perception of shading (low R/FR) via the phyB photoreceptor initiates a signaling cascade in the leaves, which ultimately transports a signal to the axillary bud that promotes tb1 transcription. tb1 expression promotes gt1 expression, leading to repression of lateral bud outgrowth in the shade. R:FR, R/FR.