Cell-to-cell mobility of the stem cell inducing WUSCHEL transcription factor is controlled by a balance of transport and retention

Non-cell autonomous induction of stem cell fate is a shared feature across multicellular organisms, however the underlying mechanisms diverge substantially between the kingdoms of live. In plants, cell to cell mobility of transcription factors has emerged as a key paradigm. For the shoot apical meristem of the reference plant Arabidopsis thaliana it has been described that the translocation of the WUSCHEL homeodomain transcription factor from niche cells to stem cells is essential for their maintenance. Here we systematically investigate the function of diverse WUS alleles and leverage multispectral live cell imaging coupled to computational analysis and mechanistic mathematical modelling to show that WUSCHEL protein mobility is the result of balance between active transport and retention in niche cells and likely independent of the stem cell signal CLAVATA3. Importantly, we show that diffusion across cell layers of the meristem is not symmetrical, suggesting that there is unexpected complexity in cellular connections.