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Title: “Spatiotemporal-specific Regulation of Floral Stem Cells”

Host: Venu Gonehal

Abstract: In an indeterminate shoot apical meristem, stem cells persist for the life of the plant. In contrast, in a determinate floral meristem, a fixed number of organs are produced before the meristem is terminated. In Arabidopsis, the floral stem cell identity is sustained by expression of the homeo-domain transcription factor WUSCHEL (WUS). Expression of WUS is terminated by multiple genetic pathways, including the zinc finger protein KNUCKLES (KNU), with the result that stem cell identity is inactivated. KNU expression is induced by the floral homeotic protein AGAMOUS (AG). The induction process requires approximately two days and entails the dynamic changes of the repressive histone modification H3K27me3 at the KNU locus. The precise temporal induction of KNU is essential for the coordinated growth and differentiation of floral stem cells. We present epigenetic mechanisms in which the floral homeotic protein AG induces KNU at approximately two days of delay. We also present how KNU represses WUS immediately. Our analyses demonstrate that specific recruitment and eviction of PcG play an essential role for the regulation of floral stem cells. We further present that the floral meristem activity is terminated in a multi-step process including hormonal control in addition to the epigenetic-mediated repression of WUS.