Integration of growth and patterning during vascular tissue formation in Arabidopsis

Coordination of cell division and pattern formation is central to tissue and organ development, and is particularly important in plants where walls prevent cell migration. Auxin and cytokinin are both critical for division and patterning, but it is unknown how these hormones converge to control tissue development. Here, we identify a genetic network that reinforces an early embryonic bias in auxin distribution to create a local, non-responding cytokinin source within the root vascular tissue. We provide experimental and theoretical evidence that these cells act as a local tissue organizer by positioning the domain of oriented cell divisions. We further demonstrate that the auxin-cytokinin interaction acts as a spatial incoherent feed forward loop, which is essential to generate distinct hormonal response zones, thus establishing a stable pattern within a growing vascular tissue. 4-day-old plants grown on MS were treated with the indicated compounds for the indicated time, whereafter roots were harvested and total RNA was isolated. Alternatively, roots were protoplasted and cell sorted for GFP+ cells followed by total RNA extraction.