Ground tissue circuitry regulates organ complexity in maize and <i>Setaria</i>.

Abstract

Most plant roots have multiple cortex layers that make up the bulk of the organ and play key roles in physiology, such as flood tolerance and symbiosis. However, little is known about the formation of cortical layers outside of the highly reduced anatomy of <i>Arabidopsis</i>. Here, we used single-cell RNA sequencing to rapidly generate a cell-resolution map of the maize root, revealing an alternative configuration of the tissue formative transcription factor SHORT-ROOT (SHR) adjacent to an expanded cortex. We show that maize SHR protein is hypermobile, moving at least eight cell layers into the cortex. Higher-order <i>SHR</i> mutants in both maize and <i>Setaria</i> have reduced numbers of cortical layers, showing that the <i>SHR</i> pathway controls expansion of cortical tissue to elaborate anatomical complexity.