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Primordia that give rise to flowers initiate from the organogenic region of the shoot apex that surrounds the central stem cell pool ( Smyth et al., 1990). They further suggest that this chromatin state switch is also involved in leaf formation and other processes in plants that are controlled by MONOPTEROS and auxin.įlowers are important for plant reproductive success and for human sustenance. Wu, Yamaguchi, Xiao et al.'s findings suggest that auxin, with the help of MONOPTEROS and the SWI/SNF remodeling complexes, enables flower formation by changing the chromatin state. These protein complexes loosen the structure of the chromatin so that genes can be switched on by transcription factors. In the presence of high levels of auxin, MONOPTEROS recruits groups of proteins called SWI/SNF remodeling complexes to regions of chromatin that contain genes involved in flower formation. The experiments show that MONOPTEROS plays a crucial role in altering the structure of chromatin to allow flowers to form. studied this question in a plant known as Arabidopsis. How the structure of the chromatin that surrounds these genes is altered so that they can be switched on is not clear. In these cells, a protein called MONOPTEROS switches on genes involved in making flowers. New flowers form from cells that contain high levels of a plant hormone called auxin. This packing prevents other proteins called transcription factors from accessing the DNA and switching the genes on. The genes are found in regions of chromatin-the structure in which DNA is packaged in plant cells-that are normally tightly packed. However, most plant cells are not able to produce a new flower or branch because the genes involved in these processes are usually switched off. Plants form new structures such as flowers or branches throughout their life as they develop and grow. They also provide an explanation for how this small molecule can direct diverse plant responses. Our findings establish a new paradigm for nuclear response to auxin. This simple and elegant hormone-mediated chromatin state switch is ideally suited for iterative flower primordium initiation and orchestrates additional auxin-regulated cell fate transitions. In the absence of the hormonal cue, auxin sensitive Aux/IAA proteins bound to MONOPTEROS block recruitment of the SWI/SNF chromatin remodeling ATPases in addition to recruiting a co-repressor/histone deacetylase complex. Upon auxin sensing, the MONOPTEROS transcription factor recruits SWI/SNF chromatin remodeling ATPases to increase accessibility of the DNA for induction of key regulators of flower primordium initiation. Here we identify an auxin hormone-regulated chromatin state switch that directs reprogramming from transit amplifying to primordium founder cell fate in Arabidopsis inflorescences. Reprogramming of cell identities during development frequently requires changes in the chromatin state that need to be restricted to the correct cell populations.