The Yin Yang of Root Regulation

The root meristem is a group of stem cells at the root tip that give rise to differentiated root tissues. The root meristem exists as a balance between new cells added by proliferation, and daughter cells removed by differentiation. The plant hormone, auxin, seems to oversee meristem cell proliferation, while the plant hormone, cytokinin, oversees differentiation. Using Arabidopsis plants, mutants, and expression and chromatin analysis, Dello Ioio et al. (p. 1380) find that signaling pathways from the two hormones converge on the SHY2 gene. Cytokinin activates the SHY2 gene, the effects of which cascade toward redistributing auxin. Auxin, on the other hand, directs degradation of the SHY2 protein, thus stabilizing auxin distribution.