Branched silkless mediates the transition from spikelet to floral meristem during Zea mays ear development

Summary The molecular and genetic control of inflorescence and flower development has been studied in great detail in model dicotyledonous plants such asArabidopsisandAntirrhinum. In contrast, little is known about these important developmental steps in monocotyledonous species. Here we report the analysis of theZea maysmutantbranched silkless1–2 (bd1–2), allelic tobd1, which we have used as a tool to study the transition from spikelet to floret development in maize. Floret development is blocked in the female inflorescence (the ear) ofbd1–2plants, whereas florets develop almost normally in the male inflorescence (the tassel). Detailed phenotypic analyses indicate that inbd1–2mutants ear inflorescence formation initiates normally, however, the spikelet meristems do not proceed to form floret meristems. The ear spikelets, at anthesis, contain various numbers of spikelet-like meristems and glume-like structures. Furthermore, growth of branches from the base of the ear is often observed. Expression analyses show that the floral-specific MADS box genesZea mays AGAMOUS1(ZAG1), ZAG2 andZea mays MADS 2(ZMM2) are not expressed in ear florets inbd1–2mutants, whereas their expression in tassel florets is similar to that of wild type. Taken together, these data indicate that the development from spikelet to floret meristem is differentially controlled in the ear and tassel in the monoecious grass speciesZea mays, and thatBRANCHED SILKLESSplays an important role in regulating the transition from spikelet meristem to floral meristem during the development of the female inflorescence of maize.